PHYSICS QUESTIONS AND ANSWERS (10)

1. The energy associated with the photon of a radio transmission at 3 x 105 Hz is
[h = 6.63 x 10-34Js]

A. 2.00 x 10-28J

B. 1.30 x 10-28J

C. 2.00 x 10- 29J

D. 1.30 x 10-29J

2. The percentage of the original nuclei of the sample of a radioactive substance left after 5 half - lives is

A. 8%

B. 5%

C. 3%

D. 1%

3. The particle that is responsible for the nuclear fission in a nuclear reactor is

A. neutron

B. proton

C. electron

D. photon

4. The maximum kinetic energy of the photoelectron emitted from a metal surface is 0.34eV. If the work function of the metal surface is 1.83eV, find the stopping potential.

A. 2.17V

B. 1.49V

C. 1.09V

D. 0.34V

[atomic masses​​ of proton, neutron and helium are​​ 1.00783U,1.00867U​​ and 4.002602U respectively]

A. 4.033U ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ B. 2.017U

C. 0.033U ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ D. 0.330U243

6. Fluorescent tubes produces light by the

A. excitation of gas molecules

B. conduction of solar energy

C. refraction of light by gas molecules

D. thermal agitation of electron in the tubes

7. The time it will take a certain radioactive material with a half-life of 50 days to reduce to 1/32 of its original number is

A. 250days

B. 150days

C. 300days

D. 200days

8. A radioactive substance has a half-life of 20 days what fraction the original radiation nuclei will remain after 80 days?

A. 1/32 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ B. 1/16

C. 1/ 8 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ D. 1/4

9. The energy E of a photon and its wavelength are related by Eλ = X. the numerical value of X is?
[h = 6.63 x 10-34Js, c = 3 x 108 ms-1]

A. 6.6 X 10-28

B. 1.99 X 10-27

C. 6.60 x 10-26

D. 1.99 x 10-25

10. When an atom undergoes a beta decay, the atomic number of the nucleus

A. Remains unchanged

B. Decreases by one

C. Increases by one

D. Becomes zero

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11. Which gas produces a red coloured light in a discharge tube?

A. Mercury

B. Argon

C. Air

D. Neon

12. Calculate the energy of the third level of an atom if the ground state energy is - 24.8eV

A. -9.20eV

B. -8.20eV

C. -2.75eV

D. -1.75eV6

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13. In photo-emission, the number of photo-electrons ejected per second depends on the

A. frequency of the beam

B. work function of the metal

C. threshold frequency of the metal

D. intensity of the beam

14. The particle nature of light is demonstrated by the

A. photoelectric effect

B. speed of light

C. colours of light

D. diffraction of light

15.​​ In a fission process, the decrease in mass is 0.01%. How much energy could be obtained from the fission of 0.1g of the material

A. ​​ 9.0×109J

B. ​​ 9.0×1010J

C. ​​ 6.3×1011J

D. 9.0×1011J

16. In a nuclear fusion experiment, the loss of mass amounts to 1.0 x 10-6kg. The amount of energy obtained from the fusion is

A. 3.0 x 10-4J ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ B. 3.0 x 10-1J

C. 9.0 x 104J ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ D. 9.0 x 1010J

17. In photoelectric effect, electrons will leave the metal surface when illuminated by light of appropriate frequency if the photon energy is

A. greater than the work function

B. less than the work function

C. equal to the work function

D. equal to the maximum kinetic energy of the electron

18.​​ If the uncertainty in the measurement of the position of a particle is 5.0 x 10-10m, the uncertainty in the momentum of the particle is

A. 1.32 x 10-44Ns

B. 3.30 x 10-44Ns

C. 1.32 x 10-24Ns

D. 3.30 x 10-24Ns162

19. A light of energy 5eV falls on a metal and the electrons with a maximum kinetic energy of 2eV are ejected. The work function of the metal is

A. 0.4eV

B. 2.5eV

C. 3.0eV

D. 7.0eV

20. Which of the following statements correctly describe(s) cathode rays?

i. they consist of tiny particles carrying negative electric charges.​​ 

ii. they are deflected in a magnetic field but not in an electric field.​​ 

iii. they consist of fast-moving neutrons and deflected in an electric field.

A. i only

B. ii only

C. i and ii only

D. ii and iii only