NEET
Practice Test 7
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Which of the following when falls on a metal will emit photo electrons ?

  • Solution

    Emission of electron from a substance under the action of light is photoelectric effect. Light must beat a sufficiently high frequency. It may be visible light, U.V,X-rays. So U.V. cause electron emission.

Which of the following shows particle nature of light?

As intensity of incident light increases

  • Solution

    Because when intensity of incident light increases, it means that number of photons increases in incident light.If number of incident photons increases, then number of emitted photo electrons also increases, consequently the photo electric current increases.

DIRECTIONS: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following-

Statement-1 :Photosensitivity of a metal is high if its work function is small.

Statement-2 :Work function = hf0 where f0 is the threshold frequency.

  • Solution

    (b)Statement-1 is true, Statement-2 is true; Statement-2 is a correct explanation for Statement-1

    Less work function means less energy is required for ejecting out the electrons.

DIRECTIONS: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following-

Statement-1 :Photoelectric saturation current increases with the increase infrequency of incident light.

Statement-2 :Energy of incident photons increases within crease in frequency and as a result photoelectric current increases.

 

  • Solution

    (d)Statement-1 is true, Statement-2 is false 64.

    Photoelectric saturation current is independent of frequency. It only depends on intensity of light.

DIRECTIONS: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following-

Statement-1 :The de-Broglie wavelength of a molecule (in a sample of ideal gas) varies inversely as the square root of absolute temperature.

Statement-2 :The rms velocity of a molecule (in a sample of ideal gas) depends on temperature.

 

  • Solution

    (a)Statement-1 is false, Statement-2 is true

    de-Broglie wavelength associated with gas molecules varies as 1

    \(\lambda \alpha \frac{1}{\sqrt{T}}\)

DIRECTIONS: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following-

Statement-1 : Though light of a single frequency(monochromatic) is incident on a metal, the energies of emitted photoelectrons are different.

Statement-2 : The energy of electrons emitted from inside the metal surface, is lost in collision with the other atoms in the metal.

  • Solution

    (a)Statement-1 is false, Statement-2 is true

    When alight of single frequency falls on the electrons of inner layer of metal, then this electron comes out of the metal surface after a large number of collisions with atom of it's upper layer.

Hard X-rays for the study of fractures in bones should have a minimum wavelength of 10–11 m. The accelerating voltage for electrons in X-ray machine should be

  • Solution

Light of frequency v falls on a material of threshold frequency v0. Maximum kinetic energy of emitted electron is proportional to

  • Solution

The anode voltage of a photocell is kept fixed. The wavelength λ of the light falling on the cathode is gradually changed. The plate current I of the photocell varies as follows

  • Solution

    As λ is increased, there will be a value of λ above which photoelectrons will be cease to come out so photo current will become zero.Hence(d) is correct answer.

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DUAL NATURE OF RADIATION AND MATTER
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