13.

A photon and an electron have the same de Broglie wavelength. Which has greater KE?

Hint: mv = √ 2mE, λ = h/ √ 2mE

14.

In the nth orbit of hydrogen atom find the ratio of radius of electron orbit and de Broglie wavelength associated with it.

Hint: rn = nh/2π mvn

λ = h/mvn

15.

Number of ejected photoelectrons increases with increase in intensity of light, but not with increase in frequency. Explain.

16.

Calculate the retarding potential needed to stop the photoelectrons ejected from a metal surface of work function 1.2 eV with light of energy 2eV.

Hint: eV0 = hν – W0

17.

The given graph shows the variation of photoelectric current with applied voltage for two different materials and for two different intensities of the incident radiation. Identify the pair of curves corresponding to different materials but same intensity of incident radiation.

18.

Two lines A and B shown in the graph represent the de Broglie wavelength (λ ) as a function of 1/√ V (V is the accelerating potential) for two particles having the same charge. Which of the two represents the particle of smaller mass?

Hint: Slope of graph = h/√2mq 1/√m

THREE MARKS QUESTIONS

19.

Show that de Broglie hypothesis of matter supports the Bohr concept of stationary orbit.

20.

Draw a graph showing the variation of stopping potential with frequency of incident radiation in relation to photoelectric effect. Deduce an expression for the slope of graph using Einstein’s photo electric equation.

21.

X rays of wavelength λ fall on a photosensitive surface, emitting electrons assuming that the work function of the surface can be neglected, prove that the de Broglie wavelength of electrons emitted will be √hλ/2mc

22.

Draw the graph showing the variation of photo current with collector potential for different intensity of incident radiation and define stopping potential.

23.

A particle is moving three times as fast as electrons. The ratio of the de Broglie wavelength of the particle to that of electron is 1.813 x 10-4, calculate the particle’s mass and identify the particle.

24.

Sketch a graph between frequency of incident radiation and stopping potential for given photosensitive material. What information can we obtain from the value of the intercept on the potential axis? A Source of light of frequency greater than threshold frequency is placed at a distance of 1 m from the cathode of