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.