Q.No.200: - What information about the structure of the nitrogen atom can be obtained from its nuclide 714N? In what way atom in 714N is different from the atom in 716N?

Q.No.200: - What information about the structure of the nitrogen atom can be obtained from its nuclide ₇¹⁴N? In what way atom in ₇¹⁴N is different from the atom in ₇¹⁶N?

Ans: -  

             ₇¹⁴N (Nitrogen): -

          Number of electrons          =         7

          Number of protons             =         7

          Number of neutrons           =    mass no - atomic no

          Number of neutrons           =     14 -7 = 7

          ₇¹⁶N (Nitrogen Isotope)

          Number of electrons          =         7

          Number of protons             =         7

          Number of neutrons           =    mass no – atomic no

          Number of neutrons           =         16 – 7 = 9

Q.No.199: - Tritium, 13H is radioactive isotope of Hydrogen. It decays by emitting an electron. What is the daughter nucleus?

Q.No.199: - Tritium, ₁³H is radioactive isotope of Hydrogen. It decays by emitting an electron. What is the daughter nucleus?

Ans: - 

Q.No.198: - How much of a 1g sample of pure radioactive mater would be left after four half-lives?

Q.No.198: - How much of a 1g sample of pure radioactive mater would be left after four half-lives?

Ans: - Amount of sample of pure radioactive matter         =      1g

           After 1^st half life 1T_1/2                                                 =   1/2g=0.5g

           After 1^st half life 2T_1/2                                                 =   0.25g

           After 1^st half life 3T_1/2                                                 =    0.125g

           After 1^st half life 4T_1/2                                                 =    0.0625g

Q.No.197: - Which type of natural radioactivity leaves the number of protons and the number of neutrons in the nucleus unchanged?

Q.No.197: - Which type of natural radioactivity leaves the number of protons and the number of neutrons in the nucleus unchanged?

Ans: - If gamma ray emit from the excited nucleus then only energy of the nucleus releases but atomic number and atomic mass remain same.

Q.No.197: - How long would you likely have to wait to watch any sample of radioactive atoms completely decay?

Q.No.197: - How long would you likely have to wait to watch any sample of radioactive atoms completely decay?

Ans: - Theoretically it will take an infinite time to decay completely because it radioactivity follow the exponential law

Q.No.196: - What is the difference between natural and artificial radioactivity?

Q.No.196: - What is the difference between natural and artificial radioactivity?

Ans: - In natural radioactivity and atomic nuclei want to became stable that’s why they emit some radiations and such atoms are called radioactive and the process is called natural radioactivity.

In artificial radioactivity the atomic nuclei which are not excited but we excite them by bombarding neutrons or protons and after excitation of nuclei the atom become radioactive and emit radiation this is called artificial radioactivity.

Q.No.195:- Which has more penetrating power, alpha particle or gamma ray photon?

Q.No.195:- Which has more penetrating power, alpha particle or gamma ray photon?

Ans: - Gamma ray is charge less and massless photon that’s why they have more penetrating power than alpha particle which have charge and mass and interact with matter so have less penetrating power.

Q.No.194: - What nuclear reaction would release more energy, the fission reaction or the fusion reaction? Explain.

Q.No.194: - What nuclear reaction would release more energy, the fission reaction or the fusion reaction? Explain.

Ans: - Fusion reaction release more energy than fission. In a Hydrogen bomb two isotopes of hydrogen, deuterium and tritium are fussed to form a nucleus of helium and a neutron. This fusion releases 17.6MeV of energy. The energy per nucleon is much greater in fusion than in fission. In fission large nuclei break apart and create small ones.  

Q.No.193: - Is it possible for an element to have different types of atoms? Explain.

Q.No.193: - Is it possible for an element to have different types of atoms? Explain.

Ans: - Yes, it is possible and it is called Isotopes. In Isotopes the number of neutrons is different but number of protons and electrons remain same of a particular atom. Hence atomic number remains same but atomic number changes and new atoms form. Like Hydrogen have 3 Isotopes.  

Q.No.192: - What is the difference between RAM and ROM memories?

Q.No.192: - What is the difference between RAM and ROM memories?

Ans: - There are several differences between them but here are only some of them mentioned.

1) RAM is the abbreviation of Random Access Memory and ROM is Read Only Memory.

2) Electricity is needed in RAM to flow to preserve information but electricity in not needed in ROM to flow for preserving information.

3) The price of RAM is comparatively high while on the other hand ROM has low price.

Q.No.191: - Which is more reliable floppy disk or a hand disk?

Q.No.191: - Which is more reliable floppy disk or a hand disk?

Ans: - Hard disk is more reliable than floppy disk. Now a days we required a large space to store data and floppy can store only some MB. While now a days we have Hard Disk or several TB, or even Hexa byte of data.

Q.No.190: - Why optical fiber is more useful tool for the communication process.

Q.No.190: - Why optical fiber is more useful tool for the communication process.

Ans: - Because in the optical fiber the light signals move faster than in open air because of some damping factor. In optical fiber we use the total internal reflection phenomenon by which the signals transmit very easily without any loss.

Q.No.189: - Show that the circuit given as below acts as AND gate.

Q.No.189: - Show that the circuit given as below acts as AND gate.

Ans: - The circuit which implements the AND operation is known as AND gate. AND gate has two or more than two inputs and only one output. The value of output of AND gate is always in accordance with the truth table of AND operation. It means output of AND gate will be 1 only when both of its inputs are at logic 1 and for all other situations output of AND gate will be 0.

Q.No.188: - Show that the circuit given as below acts as OR gate.

Q.No.188: - Show that the circuit given as below acts as OR gate.

Ans: - The electronic circuit which implements the OR operation is known as OR gate. It has two or more than two inputs and has only one output. The values of output of OR gate are always in accordance with the truth table of OR operation. It means the value of output of OR gate will be 1 when one of its inputs is at 1. The output will be 0 when both of inputs are at 0.

Q.No.187: - NAND gate is the reciprocal of AND gate. Discuss.

Q.No.187: - NAND gate is the reciprocal of AND gate. Discuss.

Ans: - In digital electronics a NAND gate is a logic gate which produces an output that is false only if all its inputs are true. A Low (0) output results only if both the inputs to the gate are High (1); if one or both inputs are low (0), a High (1) output results. 

Q.No.186: -How can you compare the logic operation X=A.B with usual operation of multiplication.

Q.No.186: -How can you compare the logic operation X=A.B with usual operation of multiplication.

Ans: - If we want to compare the logic operation with usual operation of multiplication, we will find same result as in logic operations with same inputs but if the inputs changes from 0 and 1 the logic operation will failed to give result.

Q.No.185: - In what ways is an oscilloscope a voltmeter? Ans: - How can you compare the logic operation X=A.B with usual operation of multiplication.

Q.No.185: - In what ways is an oscilloscope a voltmeter?

Ans: - For an oscilloscope, deflections is proportional to potential difference, and the CRO has high resistance, so it has all the properties of an ideal voltmeter. 

Q.No.184: - When a moving electron enters the magnetic field, it is deflected from its straight path. Name two factors which can enhance electron deflection.

Q.No.184: - When a moving electron enters the magnetic field, it is deflected from its straight path. Name two factors which can enhance electron deflection.

Ans: - If we increase the angle between velocity of electron within range 0⁰ to 90⁰ then it will enhance the deflection of electron because magnetic force is equal to F=qvBsinθ. If we increase the strength of magnetic field then it will enhance the deflection of electron.

Q.No.183: - When electrons pass through two parallel plates having opposite charges they are deflected towards the positively charged plate. What important characteristic of the electron can be inferred from this?

Q.No.183: - When electrons pass through two parallel plates having opposite charges they are deflected towards the positively charged plate. What important characteristic of the electron can be inferred from this?

Ans: - The shows that electrons have negative charge.

Q.No.182: - Give three reasons to support the evidence that cathode rays are negatively charged electrons.

Q.No.182: - Give three reasons to support the evidence that cathode rays are negatively charged electrons.

Ans: - 1) When cathode rays are created then they move to the anode of the discharge tube which shows that they are negatively charges.

2) When an electric field is applied in the discharge tube then cathode rays experiences an attractive force toward the positive plate of the applied electric field which also shows that they have negative charge.

3) By applying the magnetic field these rays stats moving in a circle. By applying Right Hand Rule we concluded that they have negative charge.

Q.No.181: - Name two factors which can enhance thermionic emission.

Q.No.181: - Name two factors which can enhance thermionic emission.

Ans: - 1) Temperature

 2) Sun light and heat is used to generate electricity and increase the efficiency of solar power production by more than twice the current levels.

Q.No.180: - Can a transformer operate on direct current?

Q.No.180: - Can a transformer operate on direct current?

Ans: - No, because transformer works in a principle of changing magnetic field creates emf and current. In DC there is no change of current and hence creates no magnetic field that’s why transformer operates in AC.

Q.No.179: - A wire lying perpendicular to an external magnetic field carries of a current in the direction shown in the diagram below. In what direction will the wire move due to the resulting magnetic force? (sorry for diagram.)

Q.No.179: - A wire lying perpendicular to an external magnetic field carries of a current in the direction shown in the diagram below. In what direction will the wire move due to the resulting magnetic force? (sorry for diagram.)

Q.No.179: - A wire lying perpendicular to an external magnetic field the magnetic field is along positive x-axis. The wire carrying a current in the direction along positive y-axis. In what direction will the wire move due to the resulting magnetic force?

Ans: - Apply Fleming Left hand rule first finger shows the direction of magnetic field and second finger shows the direction of current and the erected thumb shows the direction of force exerted by magnetic field. So in this case the force will exert in the negative z-axis.

(The direction in the figure below is opposite to that of question that’s why the direction of force will also be opposite i.e., in the downward direction.)

Q.No.178: - What reverses the direction of electric current in the armature coil of D.C. motor?

Q.No.178: - What reverses the direction of electric current in the armature coil of D.C. motor?

Ans: - To reverse the direction of current, the connection to coil is made through an arrangement of brushes and a ring that is split into halves, called a split ring commutator. Brushes which are usually pieces of graphite make contact with the commutator and allow current to flow into the loop. As the loop rotates, so does the commutator. The split ring is arranged so that each half of the commutator changes brushes just as the coil reaches the vertical position. Changing brushes reverse the current in the loop.

Q.No.177: - What is the difference between a generator and a motor?

Q.No.177: - What is the difference between a generator and a motor?

Ans: - In electric motor magnetic field rotates the coil while in electric generator we externally rotates the coil in the magnetic field.

                                                              OR

Electric motor convert electrical energy into mechanical energy and in electric generator mechanical energy is converted into electrical energy.

Q.No.176: - A conductor wire generates a voltage while moving through a magnetic field. In what direction should the wire be moved, relative to the field to generate the maximum voltage?

Q.No.176: - A conductor wire generates a voltage while moving through a magnetic field. In what direction should the wire be moved, relative to the field to generate the maximum voltage?

Ans: - When we place a conductor wire in a magnetic field then it will experience a magnetic force in the direction perpendicular to the magnetic field. To generate the maximum voltage (emf) in the conductor we must move the wire in such a way that angle between velocity or wire and magnetic field must be 90⁰. 

Q.No.175: - Suppose we hang a loop of wire so that it can swing easily. If we now put a magnet into the coil, the coil will start swinging. Which way will it swing relative to the magnet and why?

Q.No.175: - Suppose we hang a loop of wire so that it can swing easily. If we now put a magnet into the coil, the coil will start swinging. Which way will it swing relative to the magnet and why?

Ans: - As we know the law of electromagnetic induction; is Lenz’s law, states that the direction of the induced e.m.f is always such as to oppose the change producing it.

Q.No.174: - Which device is used for converting electrical energy into mechanical energy?

Q.No.174: - Which device is used for converting electrical energy into mechanical energy?

Ans: - Electric motor is used for converting electrical energy into mechanical energy.

Q.No.173: - Suppose you have a coil of wire and a bar magnet. Describe how you could use them to generate an electric current.

Q.No.173: - Suppose you have a coil of wire and a bar magnet. Describe how you could use them to generate an electric current.

Ans: - We will move the bar magnet into and out of the coil and this changing magnetic field will induce emf and electric current.

Q.No.172: - Suppose someone handed you three similar iron bars and told you one was not magnet but the other two were. How would you find the iron bar that was not magnet?

Q.No.172: - Suppose someone handed you three similar iron bars and told you one was not magnet but the other two were. How would you find the iron bar that was not magnet?

Ans: - We will place compass needle near these three iron bar. The compass needle will show response near magnet. So when we take compass needle near the iron bar and if this compass needle did not changes its direction then this means that this iron bar is not a magnet.

Q.No.171: - Explain why, a glass rod can be charged by rubbing when held by hand but an iron rod cannot be charged by rubbing, if held by hand?

Q.No.171: - Explain why, a glass rod can be charged by rubbing when held by hand but an iron rod cannot be charged by rubbing, if held by hand?

Ans: - Because iron is a conductor so when we rub it then electrons move within the conductor and did not become static on the other hand glass rod is an insulator and when we rub, it get charge on its surface and act like a charged body.

Q.No.170: - If a high-voltage power line fell across your car while you were in the car, why should you not come out of the car?

Q.No.170: - If a high-voltage power line fell across your car while you were in the car, why should you not come out of the car?

Ans: - When a high voltage power line fell across your car then the tires between your body and the ground act as insulator and in this way we remain safe in the car and we will not come out of the car. In this case the car acts like a Faraday-cage.  

Q.No.169: - Perhaps you have seen a gasoline truck trailing a metal chain beneath it. What purpose does the chain serve?

Q.No.169: - Perhaps you have seen a gasoline truck trailing a metal chain beneath it. What purpose does the chain serve?

Ans: - When the truck moves then its body gets charge due to air friction and the purpose of trailing metal chain beneath it is that, the charge will transfer to the ground.

Q.No.168: - Rubber tires get charged from friction with the road. What is the polarity of the charge?

Q.No.168: - Rubber tires get charged from friction with the road. What is the polarity of the charge?

Ans: - When two materials rubbed together then they will transfer electron the one who get electrons become negatively charged and the other who lose this charge gets positive charge. When tires rubbed with road then road will transfer electrons to the tires hence tires get negative charge and the road who transfer electrons get positive charge.

Q.No.167: - Is the presence of charge necessary for the existence of electrostatic potential?

Q.No.167: - Is the presence of charge necessary for the existence of electrostatic potential?

Ans: - Yes, electrostatic potential will exists when there is a static charge.

Q.No.166: - Each capacitor in parallel combination has equal potential difference between its two plates. Justify the statement.

Q.No.166: - Each capacitor in parallel combination has equal potential difference between its two plates. Justify the statement.

Ans: - As current flow in each capacitor is same that’s why the potential of each capacitor across its plates is same.

                                                   OR

In this method left plates of all the capacitors are connected to one point and the right ones connected to another point.

Q.No.165: - Dose each capacitor carry equal charge in series combination? Explain.

Q.No.165: - Dose each capacitor carry equal charge in series combination? Explain.

Ans: - Yes, when capacitors are connected in series then all the capacitors have equal charge on their plates. But the voltage of each capacitor is different.

Q.No.164: - In what direction will a positively charged particle move in an electric field?

Q.No.164: - In what direction will a positively charged particle move in an electric field?

Ans: - If the electric field is due to positive charge and we place a positive charge in this electric field then this charge will move along the electric field line or we can say that this charge will move in the direction of arrow head of the field. If the field is due to negative charge then the positive charge will move in the opposite direction i.e; towards the tails of the electric field.

Q.No.163: - How much negative charge has been removed from a positively charged electroscope if it has a charge of 7.5x10-11C?

Q.No.163: - How much negative charge has been removed from a positively charged electroscope if it has a charge of 7.5x10^-11C?

Ans: - Negative and positive charge are equal in magnitude. So, if electroscope has 7.5x10^-11C  of positive charge then it mean that 7.5x10^-11C of negative charge has been removed.

Q.No.162: - An electrified rod attracts pieces of paper. After a while these pieces fly away! Why?

Q.No.162: - An electrified rod attracts pieces of paper. After a while these pieces fly away! Why?

Ans: - Electrified rod has more number of electrons when we took this rod near to the piece of paper which is neutral the charge from rod shifts to the paper after the transfer of charge the paper get charged and now both have equal number on electrons. Now these electrons exert a repulsive force on each other. That’s why after a while paper pieces fly away.

Q.No.161: - Why ultrasound is useful in medical field?

Q.No.161: - Why ultrasound is useful in medical field?

Ans: - By ultrasound we can check the inner condition of patient that’s why it is much useful in medical science.

Q.No.160: - Will two separate 50dB sounds together constitute a 100dB sound? Explain.

Q.No.160: - Will two separate 50dB sounds together constitute a 100dB sound? Explain.

Ans: - No, two separate 50dB sounds together do not constitute a 100dB sound because dB is an exponential scale. Each ten dB increase in sound makes the sound ten times louder. An increase of 50dB makes the sound 10⁴ times louder. Hence it will not make 100dB but twice as loud is an increase of 10Log (2) = 3.01dB. So 53.01dB is twice as loud as 50dB. 

Q.No.159: - Is there any difference between echo and reflection of sound? Explain.

Q.No.159: - Is there any difference between echo and reflection of sound? Explain.

Ans: - No, there is no difference between echo and reflection. Echo can be defined as, when sound is incident on the surface of a medium it bounces back into the first medium. This phenomenon is also called reflection of sound.

Q.No.158:- Two people are listening to the same music at the same distance. They disagree on its loudness. Explain how this could happen?

Q.No.158:- Two people are listening to the same music at the same distance. They disagree on its loudness. Explain how this could happen?

Ans: - If the distance of listener from source is same and medium is also same and they both are disagreeing with the loudness then there is a problem in their ear.

Q.No.157: - A student says that the two terms speed and frequency of the wave refer to the same thing. What is your response?

Q.No.157: - A student says that the two terms speed and frequency of the wave refer to the same thing. What is your response?

Ans: - Speed of a wave is how fast the wave is moving in a medium while the frequency of wave is the number of cycle per unit of time. So these two things are not same.

Q.No.156: - Why must the volume of a stereo in a room with wall-to-wall carpet is turned higher than in a room with a wooden floor?

Q.No.156: - Why must the volume of a stereo in a room with wall-to-wall carpet is turned higher than in a room with a wooden floor?

Ans: - Volume of a stereo in a room with wall to wall carpet must be tuned higher than in a room with a wooden floor because reflection of sound is more prominent if the surface is smooth, and less if the surface is irregular.

Q.No.155: - You can listen to your fried round a corner, but you cannot watch him/her. Why?

Q.No.155: - You can listen to your fried round a corner, but you cannot watch him/her. Why?

Ans: - You can listen your friend round a corner because waves can propagate from solid medium.

Q.No.154: - We can recognize persons speaking with the same loudness from their voice. How is this possible?

Q.No.154: - We can recognize persons speaking with the same loudness from their voice. How is this possible?

Ans: - we can recognize persons speaking with the same loudness from their voice because their quality of sound is different. Quality of sound is the characteristic by which we can distinguish between two sounds of same loudness and pitch. The waveforms of sound produced by persons are different. So their quality is different and they can be distinguished from each other. 

Q.No.153: - Why two tin cans with a string stretched between them could be better way to communicate than merely shouting through the air?

Q.No.153: - Why two tin cans with a string stretched between them could be better way to communicate than merely shouting through the air?

Ans: - When two tin cans are attached with a stretched string then the string becomes a medium that transmit sound wave from one can to the other. String is a solid and it makes a batter medium of transmitting sound wave rather than air. When we shout in air then air carries sound with low speed than a stretched string.

Q.No.152: - Does a fuse in a circuit control, the potential difference or the current?

Q.No.152: - Does a fuse in a circuit control, the potential difference or the current?

 Ans: - Fuse in a circuit controls the excess amount of current.

Q.No.151: - It is impracticable to connect an electric bulb and an electric heater in series. Why?

Q.No.151: - It is impracticable to connect an electric bulb and an electric heater in series. Why?

Ans: - In series connection current remains same and voltage divided according to the resistance of the appliance. When we put electric bulb and electric heater in series then it will divide the voltage which ultimately divided the power double.

Q.No.150: - A certain flash-light can use a 10ohm bulb or a 5ohm bulb. Which bulb should be used to get the brighter light? Which bulb will discharge the battery first?

Q.No.150: - A certain flash-light can use a 10ohm bulb or a 5ohm bulb. Which bulb should be used to get the brighter light? Which bulb will discharge the battery first?

Ans: - If the bulbs are connected in parallel then they will have same brightness because the brightness depends upon the voltage. If the bulbs are connected in series then first bulb will be brighter than the second because in series the voltage drop is different in two bulbs. The bulb which has more resistance will discharge the battery soon.

Q.No.149: - From your experience in watching cars on the roads at night, are automobile head lamps connected in series or in parallel?

Q.No.149: - From your experience in watching cars on the roads at night, are automobile head lamps connected in series or in parallel?

Ans: - The head light of cars are connecting in parallel because their brightness are approximately same. If they are connected in series then first light will be brighter than the second light. In series potential will drop in both headlights. While in parallel potential will remain same and they will have same brightness.

                                                              OR

Head lamps of automobiles are generally wired in parallel. This way, if one headlight is to burn out the others remain switched ON.

Q.No.148: - How many watt-hours are there in 1000 joules?

Q.No.148: - How many watt-hours are there in 1000 joules?

Ans: -

          1kwhr           =         3.6x10⁶J

          1whr             =         3.6x10⁶J/10³

          1whr             =         3.6x10^6-3J

          1whr             =         3.6x10³J

          1whr/3.6x10³         =         1J
          0.000278whr         =         1J

          1000x0.000278watt hr   =         1000x1J

          0.27778watt hr                =         1000J

Q.No.147: - In order to measure voltage in a circuit voltmeter is always connected in parallel. Discuss.

Q.No.147: - In order to measure voltage in a circuit voltmeter is always connected in parallel. Discuss.

Ans: - The potential difference is a measure of voltage difference between two points that’s why we apply voltmeter across two points which will make a parallel connection not a series connection unlike ammeter which has series connection.

Q.No.146: - In order to measure current in a circuit why ammeter is always connected in series?

Q.No.146: - In order to measure current in a circuit why ammeter is always connected in series?

Ans: - According to the definition of electric current. Number of charges passing through a point in a unit time is called electric current. So from this definition we can say that electric current associated to the points of the conductor, that’s why we must apply it in series not in parallel. 

Q.No.145: - Two points on an object are at different electric potentials. Does charge necessarily flow between them?

Q.No.145: - Two points on an object are at different electric potentials. Does charge necessarily flow between them?

Ans: - Electric current flow due to the potential difference. If the object is conductor and there is a potential difference occurs between to different points then electric current will flow. But if the object is insulator then no current will flow.

Q.No.144: - Can current flow in a circuit without potential difference?

Q.No.144: - Can current flow in a circuit without potential difference?

Ans: - No, emf is responsible for the flow of current. When we apply a battery to the ends of a conductor then due to the potential difference between the ends of battery free electrons in the conductor move and respond to the external electric field applied. So, we can say that without potential difference there is no concept of current flow.

Q.No.143: - What is the difference between a cell and a battery?

Q.No.143: - What is the difference between a cell and a battery?

Ans: - A cell is a single unit at the base voltage. A battery can be a single cell or multiple cells connected together in series or parallel to make the voltage/current rating desired. 

Q.No.142: - Why in conductors charge is transferred by free electrons rather than by positive charges?

Q.No.142: - Why in conductors charge is transferred by free electrons rather than by positive charges?

Ans: - Because electrons are free in conductor and they are in majority. When we apply an external electric field with the help of a battery (source of emf) then these free electrons move from negative to positive terminal of battery. On the other side, positive charges are present in the nucleus of the atom and they are not free to move that’s why electric current is caused by free electrons.

Q.No.141: - What are non ferromagnetic materials?

         Q.No.141: - What are non ferromagnetic materials?

         Ans: - Materials that transmit light are normally non-ferromagnetic materials

Q.No.140: - Why the speed of light is different in different material rather than vaccum?

         Q.No.140: - Why the speed of light is different in different material rather than vaccum?

        Ans: - The light is basically an electromagnetic wave. When light enters in a material then electric and magnetic properties of the medium effect on the electric and magnetic components of the light (electromagnetic wave) that’s why the speed of light in matter changes. Materials that transmit light are normally non-ferromagnetic

Q.No.139: - Define phosphorescent also describe the factors upon which it depends.

Q.No.139: - Define phosphorescent also describe the factors upon which it depends.

Ans: - Objects that continue to glow longer than 10^-8s after the source of the excitation is removed are called phosphorescent and the material that causes this effect is called phosphor. For example, dial of clock. It depend on the duration of light emission after the source of excitation is removed.

Q.No.138: - What is meant by fluorescent? On which factor it depends?

Q.No.138: - What is meant by fluorescent? On which factor it depends?

Ans: - Objects in which the emission of light ceases immediately (within

10^-8s) after the excitation is removed are called fluorescent. It depends upon the duration of light emission after the source of excitation is removed. The example is fluorescent lamp.

Q.No.137: - How fluorescent lamp works?

Q.No.137: - How fluorescent lamp works?

Ans: - In the case of fluorescent lamp an electric current passed through the gas in the tube causes the electrons to move to higher energy states. When the electrons return to their original energy states, they give up their excess energy in the form of ultraviolet radiation. This radiation is absorbed by atoms of the coating on the inside of the glass tube, which then emit visible light.

Q.No.136: -What is Doppler Effect?

Q.No.136: -What is Doppler Effect?

Ans: - The change in frequency due to the relative motion is called Doppler Effect.

Q.No.135: - Describe the dispersion on atomic scale.

Q.No.135: - Describe the dispersion on atomic scale.

Ans: - The electric field of the incident light causes the electrons in an atom to oscillate with the frequency of the incident light. When the incident and scattered waves interfere the phase of their combination depends on their difference and hence on the frequency. As a result, the speed of light in a material depends on the frequency or wavelength. This phenomenon called dispersion.

Q.No.134: - What is the microscopic reason of dispersion?

Q.No.134: - What is the microscopic reason of dispersion?

Ans: - The electric field of the incident light causes the electrons in an atom to oscillate with the frequency of the incident light. When the incident and scattered waves interfere the phase of their combination depends on their difference and hence on the frequency. As a result, the speed of light in a material depends on the frequency or wavelength. This phenomenon called dispersion.

Q.No.133: - Describe the dispersion phenomena.

Q.No.133: - Describe the dispersion phenomena.

Ans: - The electric field of the incident light causes the electrons in an atom to oscillate with the frequency of the incident light. When the incident and scattered waves interfere the phase of their combination depends on their difference and hence on the frequency. As a result, the speed of light in a material depends on the frequency or wavelength. This phenomenon called dispersion.

Q.No.132: - What will be the effect on the measure of dielectric constant if light with high frequency (electromagnetic wave with varying E and B field) passes through the material medium?

Q.No.132: - What will be the effect on the measure of dielectric constant if light with high frequency (electromagnetic wave with varying E and B field) passes through the material medium?

Ans: - When we apply a field varies at high frequency then the dipoles may not have time to respond and we can’t use the static dielectric constants in the case of a rapidly varying E and B field. Further more the value of dielectric constant varies with frequency, so that the speed of light in matter depends on the wavelength or frequency of light.

Q.No.131: - Define dielectric constant.

Q.No.131: - Define dielectric constant.

Ans: - When light (electromagnetic wave) pass through the material then the dipoles (permanent or induced) give response to the applied electric field basically the dielectric constant is in effect a measure of the response of the dipoles. 

Q.No.130: - On which thing (effect) the dielectric constant respond in a material?

Q.No.130: - On which thing (effect) the dielectric constant respond in a material?

Ans: - When light (electromagnetic wave) pass through the material then the dipoles (permanent or induced) give response to the applied electric field basically the dielectric constant is in effect a measure of the response of the dipoles. 

Q No.129: - (a):-Is it possible to have a purely electric wave propagate through empty space that is, a wave made up of an electric field but no magnetic field? (b) What about a purely magnetic wave, with a magnetic field but no electric field?

Q.No.129: - (a):-Is it possible to have a purely electric wave propagate through empty space that is, a wave made up of an electric field but no magnetic field? (b) What about a purely magnetic wave, with a magnetic field but no electric field? 
Answer: - (a) no (b) no, A purely electric wave would have a varying electric field. Such a field necessarily generates a magnetic field through Ampere's law, So a purely electric wave is impossible. In the same way, a purely magnetic wave is impossible: The varying magnetic field in such a wave would automatically give rise to an electric field through Faraday's Law.
Reference: -
Sears and Zemansky's University Physics with modern Physisc by Hugh D. Young Roger A. Freedman 12th Edition Chapter no 32 question is on page no 1096 and answer is on 1116

Q.No.128(b): - What is the microscopic reason of dispersion?

Q.No.128(b): - What is the microscopic reason of dispersion?

Ans: - The electric field of the incident field of the incident light causes the electron in an atom to oscillate with the frequency of the incident light. When the incident and scattered waves interfere then the phase of their combination depends on their phase difference and hence on the frequency. As a result, the speed of light in a material depends on the frequency or wavelength. This phenomenon is called dispersion.

Q.No.129: - What is Doppler Effect?

Q.No.129: - What is Doppler Effect?

Ans: - The change in frequency due to the relative motion is called Doppler Effect.

Q.No.128(c): - Describe the dispersion phenomenon. Or What is the microscopic reason of dispersion? Or Describe the dispersion on atomic scale. Ans: - The electric field of the incident field of the incident light causes the electron in an atom to oscillate with the frequency of the incident light. When the incident and scattered waves interfere then the phase of their combination depends on their phase difference and hence on the frequency. As a result, the speed of light in a material depends on the frequency or wavelength. This phenomenon is called dispersion.

Q.No.128(c): -Describe the dispersion on atomic scale.

Ans: - The electric field of the incident light causes the electron in an atom to oscillate with the frequency of the incident light. When the incident and scattered waves interfere then the phase of their combination depends on their phase difference and hence on the frequency. As a result, the speed of light in a material depends on the frequency or wavelength. This phenomenon is called dispersion.

Q.No.128(a): - Describe the dispersion phenomenon.

Q.No.128(a): - Describe the dispersion phenomenon.

Ans: - The electric field of the incident light causes the electron in an atom to oscillate with the frequency of the incident light. When the incident and scattered waves interfere then the phase of their combination depends on their phase difference and hence on the frequency. As a result, the speed of light in a material depends on the frequency or wavelength. This phenomenon is called dispersion.

Q.No.125: - Define phosphorescent also describe the factors upon which it depends?

Q.No.125: - Define phosphorescent also describe the factors upon which it depends?

Ans: - Objects that continue to glow longer than 10^-8s after the source of the excitation is removed are called phosphorescent and the materials that cause this effect is called a phosphor. For example dial of clock. It depends on the duration of light emission after the source of excitation is removed.

Q.No.126: - What are the causes of luminescence? Describe them briefly.

Q.No.126: - What are the causes of luminescence? Describe them briefly.

Ans: - Luminescence can have a variety of causes some of them are given below.

i)                   Chemiluminescence:- When the energy that excites the atoms originates from a chemical reaction is called Chemiluminescence .

ii)                Bioluminescence:- Often the effect occurs in living things, such as in fireflies and many marine organisms, in this case it is called bioluminescence.

iii)              Triboluminescence:- Light can also be emitted when certain crystals for example, sugar are crushed the effect called Triboluminescence.

Q.No.124: - What is meant by fluorescent? On which factor it depends?

Q.No.124: - What is meant by fluorescent? On which factor it depends?

Ans: - Objects in which the emission of light ceases immediately (within 10^-8s) after the source of the excitation is removed are called fluorescent. It depends upon the duration of light emission after the source of excitation is removed. The example is fluorescent lamp.

Q.No.123(a): - How fluorescent lamp works?

Q.No.123(a): - How fluorescent lamp works?

Ans:- In the case of fluorescent lamp, an electric current passed through the gas in the tube causes the electrons to move to higher energy states; when the electrons return to their original energy states, they give up their excess energy in the form of ultraviolet radiation. This radiation is absorbed by atoms of the coating on the inside of the glass tube, which then emit visible light.

Q.No.123(b): -Who fluorescent lamps radiate light?

Q.No.123(b): -Who fluorescent lamps radiate light?

Ans:- In the case of fluorescent lamp, an electric current passed through the gas in the tube causes the electrons to move to higher energy states; when the electrons return to their original energy states, they give up their excess energy in the form of ultraviolet radiation. This radiation is absorbed by atoms of the coating on the inside of the glass tube, which then emit visible light.

Q.No.122: - Can light emit from cool objects? If yes then what is it called?

Q.No.122: - Can light emit from cool objects? If yes then what is it called?

Ans: - Yes cool bodies also emit visible light and this phenomenon is called luminescence. Examples are common fluorescent lamps, glowing of watch and clock dials, and television receivers.

Q.No.119: - Which velocity of wave may greater than the speed of light “c”?

Q.No.119: - Which velocity of wave may greater than the speed of light “c”?

Ans: - The phase velocity of light may increase the speed of light but the group velocity is always less than the speed of light.

Q.No.221: - What is meant by incandescent object? How can we body made incandescent?

Q.No.221: - What is meant by incandescent object? How can we body made incandescent?

Ans: - An object whose thermal radiation is visible is called incandescent like Sun. Typically if the temperature of the body exceeds 1000^oC then the body will become incandescent.

Q.No.120: - What are thermal radiations?

Q.No.120: - What are thermal radiations?

Ans: - All objects emit electromagnetic radiation, called thermal radiation, because of their temperature.

Q.No.118: - By which velocity the modulated wave (information) travels?

Q.No.118: - By which velocity the modulated wave (information) travels?

Ans: - The modulated information (wave) travels with group velocity not with phase velocity.

Q.No.117: - Why it is necessary to modulate radio wave?

Q.No.117: - Why it is necessary to modulate radio wave?

Ans: - Because an infinitely long wave train of constant amplitude cannot carry information. The carrier of radio wave, for instance, carries no information until it is modulated.

Q.No.116: - If light emitted from a single molecule is polarized then why the light emitted from incandescent and fluorescent light bulb is unpolarized?

Q.No.116: - If light emitted from a single molecule is polarized then why the light emitted from incandescent and fluorescent light bulb is unpolarized?

Ans: - Incandescent and fluorescent light bulbs contain molecules. These molecules emit polarized light individually but this light depends on the orientation of molecules and the orientation of each molecule is different in the bulb. That’s why the result of all these polarized lights coming from each molecule into unpolarized light.

Q.No.115: - Which type of light is emitted from a single molecule?

Q.No.115: - Which type of light is emitted from a single molecule?

Ans: - A single molecule emits polarized light. The direction of light depends upon the orientation of molecule.

Q.No.113: - What is meant by linear polarized wave? How can we make a wave linearly polarized?

Q.No.113: - What is meant by linear polarized wave? How can we make a wave linearly polarized?

Ans: - When a wave have only one component along anyone dimension i.e. along-x, y or z-axis that wave is called linearly polarized. We can make a wave linearly polarized by using polarizing filter.

Q.No.112: - What is meant by dispersion?

Q.No.112: - What is meant by dispersion?

Ans: - The dependence of wave speed and index of refraction on wavelength is called dispersion.

Q.No.111(c): - Why ordinary light disperses from any other dense medium?

Q.No.111(c): - Why ordinary light disperses from any other dense medium?

Ans: - As we know that white light is the superposition of waves with wavelengths of visible spectrum and the speed of light in air or vacuum is the same for all wavelengths, but the speed in a material substance is different for different wavelengths. That’s why when white light passes through material medium then it splits because it doesn’t consists of single wavelength but many wavelengths. This is called dispersion

Q.No.111(b): -Explain the phenomenon of dispersion.

Q.No.111(b): -Explain the phenomenon of dispersion.

Ans: - As we know that white light is the superposition of waves with wavelengths of visible spectrum and the speed of light in air or vacuum is the same for all wavelengths, but the speed in a material substance is different for different wavelengths. That’s why when white light passes through material medium then it splits because it doesn’t consists of single wavelength but many wavelengths. This is called dispersion

Q.No.111(a): - Why white light splits in material than in air?

Q.No.111(a): - Why white light splits in material than in air?

Ans: - As we know that white light is the superposition of waves with wavelengths of visible spectrum and the speed of light in air or vacuum is the same for all wavelengths, but the speed in a material substance is different for different wavelengths. That’s why when white light passes through material medium then it splits because it doesn’t consists of single wavelength but many wavelengths. This is called dispersion

Q.No.110: - How ordinary white light forms?

Q.No.110: - How ordinary white light forms?

Ans: - Ordinary white light is the superposition of waves with wavelengths extending throughout the visible spectrum.

Q.No.109(a): - Which condition of material, refractive index, wave speed and wavelength must satisfy for total internal reflection?

Q.No.109(a): -  Which condition of material, refractive index, wave speed and wavelength must satisfy for total internal reflection?

Ans: - When a ray passes from two media of different refractive index. Then the medium of incoming ray must have greater refractive index than the other i.e. the medium must be denser of incoming ray. Similarly the wave speed and wavelength of incoming ray must be smaller or shorter. Furthermore total internal reflection will occur if the angle of incident is larger than or equal to critical angle.

Q.No.109: - When total internal reflection occurs?

Q.No.109: - When total internal reflection occurs?

Ans: - When a ray passes from two media of different refractive index. Then the medium of incoming ray must have greater refractive index than the other i.e. the medium must be denser of incoming ray. Similarly the wave speed and wavelength of incoming ray must be smaller or shorter. Furthermore total internal reflection will occur if the angle of incident is larger than or equal to critical angle.

Q.No.108: - What is meant by total internal reflection?

Q.No.108: - What is meant by total internal reflection?

Ans: - If the angle of incidence is larger than the critical angle, the sine of the angle of refraction, as computed by Snell’s law, would have to be greater than unity, which is impossible. Beyond the critical angle, the ray cannot pass into the upper material; it is trapped in the lower material and is completely reflected at the boundary surface. This situation is called “total internal reflection”.

Q.No.106: - what is the relation between wave speed, refractive index, wavelength and the properties (condition) of medium. Explain.

Q.No.106: - what is the relation between wave speed, refractive index, wavelength and the properties (condition) of medium. Explain.

Ans: - If the medium is dense then wave speed then wave speed in this material will low as compared to wave speed in vacuum so the ratio of speed in vacuum over dense medium will be greater than unity. This ratio is refractive index.

                                n     =      c/v      =       vacuum/dense medium      >       1

or we can say that if refractive index is greater than unity then wave is passing through the denser medium where wave speed is less than as in vacuum.

         As,                             v        =         f.λ

Frequency remains same in every material. So velocity v is directly proportional to λ (lambda) wavelength. So if speed of wave changes then wavelength also changes. On the other hand if refractive index also depends upon wavelength. So we can say that in denser medium wave speed decrease so wavelength also decrease (shorter or squeezed).