Chap#18 Dawn of Modern Physics

Question 1

A photocell with a constant p.d. of V volt across it illuminated by a point source from a distance of 25 cm. When the source is moved to a distance of 1m, the electrons emitted by the photocell:

Answer 1

Are 1/16th as numerous as before

Question 2

A monochromatic source of light is placed at a large distance d from a metal surface. Photoelectrons are ejected at rate n, kinetic energy being E. If the source is brought nearer to distance d/2, the rate and kinetic energy per photoelectron become nearly

Answer 2

4n and E

Question 3

The frequency of the incident light falling on a photosensitive metal plate is doubled, the kinetic energy of the emitted photoelectron is:

Answer 3

More than doubled

Question 4

When light of wavelength 300nm (nanometer) falls of a photoelectric emitter, photoelectron are liberated. For another emitter, however, light of 600 nm wavelength is sufficient for creating photoemission. What is the ratio of the work functions of the emitters

Answer 4

2:1

Question 5

Ultra-violet radiation of 6.2 eV falls on an aluminum surface. K.E.E of the fastest electron emitted is: (Work function = 4.2 eV)

Answer 5

3.2 x 10^-21 J

Question 6

A photoelectric cell converts:

Answer 6

Light energy to electrical energy

Question 7

The essential distinction between X-rays and γ-rays is that:

Answer 7

γ-rays emanate from nucleus

Question 8

A beam of light of wavelength γ and with illumination L falls on a clean surface of sodium. If N photoelectrons are emitted each with kinetic energy E, then:

Answer 8

N ∝ L and E ∝1/λ

Question 9

The minium wavelength of the X-rays produced by electrons accelerated through a potential difference of V volts is directly proportional to:

Answer 9

1/V