Science (English Medium) Class 12 - CBSE Important Questions

Define the term "Threshold frequency", in the context of photoelectric emission.  

Define the term: threshold frequency

Answer the following question.
Plot a graph of photocurrent versus anode potential for radiation of frequency ν and intensities I₁ and I₂ (I₁ < I₂).

Answer the following question.
Obtain the expression for the ratio of the de-Broglie wavelengths associated with the electron orbiting in the second and third excited states of the hydrogen atom.

On the basis of the graphs shown in the figure, answer the following questions :

(a) Which physical parameter is kept constant for the three curves?

(b) Which is the highest frequency among v₁, v_2, and v₃?

Use Einstein's photoelectric equation to show how from this graph,
(i) Threshold frequency, and
(ii) Planck's constant can be determined.

The work function of aluminum is 4⋅2 eV. If two photons each of energy 2⋅5 eV are incident on its surface, will the emission of electrons take place? Justify your answer.

Define the terms "stopping potential' and 'threshold frequency' in relation to the photoelectric effect. How does one determine these physical quantities using Einstein's equation?

Choose the correct answer from given options
Photons of frequency v are incident on the surface of two metals A and B of threshold frequency 3/4 v and 2/3 v, respectively. The ratio of maximum kinetic energy of electrons emitted from A to that from B is

In the case of a photo electric effect experiment, explain the following facts, giving reasons.
The wave theory of light could not explain the existence of the threshold frequency.

In the case of photoelectric effect experiment, explain the following facts, giving reasons.
The photoelectric current increases with increase of intensity of incident light.

Define the term: stopping potential in the photoelectric effect.

Explain how does (i) photoelectric current and (ii) kinetic energy of the photoelectrons emitted in a photocell vary if the frequency of incident radiation is doubled, but keeping the intensity same?

Show the graphical variation in the above two cases.

Light of wavelength 2000 Å falls on a metal surface of work function 4.2 eV.

What is the kinetic energy (in eV) of the fastest electrons emitted from the surface?

Light of wavelength 2000 Å falls on a metal surface of work function 4.2 eV.

What will be the change in the energy of the emitted electrons if the intensity of light with same wavelength is doubled?

Light of wavelength 2000 Å falls on a metal surface of work function 4.2 eV.

If the same light falls on another surface of work function 6.5 eV, what will be the energy of emitted electrons?

The work function for a metal surface is 4.14 eV. The threshold wavelength for this metal surface is ______.

Radiation of frequency 10¹⁵ Hz is incident on three photosensitive surfaces A, B and C. Following observations are recorded:

Surface A: no photoemission occurs

Surface B: photoemission occurs but the photoelectrons have zero kinetic energy.

Surface C: photo emission occurs and photoelectrons have some kinetic energy.
Using Einstein’s photo-electric equation, explain the three observations.

The graph shows the variation of photocurrent for a photosensitive metal

1. What does X and A on the horizontal axis represent?
2. Draw this graph for three different values of frequencies of incident radiation ʋ₁, ʋ₂ and ʋ₃ (ʋ₃ > ʋ₂ > ʋ₁) for the same intensity.
3. Draw this graph for three different values of intensities of incident radiation I₁, I₂ and I₃ (I₃ > I₂ > I₁) having the same frequency.

(i) A ray of light incident on face AB of an equilateral glass prism, shows minimum deviation of 30°. Calculate the speed of light through the prism.

(ii) Find the angle of incidence at face AB so that the emergent ray grazes along the face AC.