Science (English Medium) Class 12 - CBSE Question Bank Solutions for Physics

Consider sunlight incident on a slit of width 10⁴ A. The image seen through the slit shall ______.

Consider sunlight incident on a pinhole of width 10³A. The image of the pinhole seen on a screen shall be ______.

1. a sharp white ring.
2. different from a geometrical image.
3. a diffused central spot, white in colour.
4. diffused coloured region around a sharp central white spot.

The wavelength of a photon needed to remove a proton from a nucleus which is bound to the nucleus with 1 MeV energy is nearly ______.

1. In the explanation of photo electric effect, we assume one photon of frequency ν collides with an electron and transfers its energy. This leads to the equation for the maximum energy E_max of the emitted electron as E_max = hν – φ₀  where φ₀ is the work function of the metal. If an electron absorbs 2 photons (each of frequency ν) what will be the maximum energy for the emitted electron?
2. Why is this fact (two photon absorption) not taken into consideration in our discussion of the stopping potential?

There are materials which absorb photons of shorter wavelength and emit photons of longer wavelength. Can there be stable substances which absorb photons of larger wavelength and emit light of shorter wavelength.

A student performs an experiment on photoelectric effect, using two materials A and B. A plot of V_stop vs ν is given in Figure.

1. Which material A or B has a higher work function?
2. Given the electric charge of an electron = 1.6 × 10^–19 C, find the value of h obtained from the experiment for both A and B.

Comment on whether it is consistent with Einstein’s theory:

The Balmer series for the H-atom can be observed ______.

1. if we measure the frequencies of light emitted when an excited atom falls to the ground state.
2. if we measure the frequencies of light emitted due to transitions between excited states and the first excited state.
3. in any transition in a H-atom.
4. as a sequence of frequencies with the higher frequencies getting closely packed.

Let E_n = `(-1)/(8ε_0^2) (me^4)/(n^2h^2)` be the energy of the nth level of H-atom. If all the H-atoms are in the ground state and radiation of frequency (E₂ - E₁)/h falls on it ______.

1. it will not be absorbed at all.
2. some of atoms will move to the first excited state.
3. all atoms will be excited to the n = 2 state.
4. no atoms will make a transition to the n = 3 state.

Positronium is just like a H-atom with the proton replaced by the positively charged anti-particle of the electron (called the positron which is as massive as the electron). What would be the ground state energy of positronium?

In the Auger process an atom makes a transition to a lower state without emitting a photon. The excess energy is transferred to an outer electron which may be ejected by the atom. (This is called an Auger electron). Assuming the nucleus to be massive, calculate the kinetic energy of an n = 4 Auger electron emitted by Chromium by absorbing the energy from a n = 2 to n = 1 transition.

In Figure, Vo is the potential barrier across a p-n junction, when no battery is connected across the junction ______.

In the circuit shown in figure, if the diode forward voltage drop is 0.3 V, the voltage difference between A and B is ______.

When an electric field is applied across a semiconductor ______.

1. electrons move from lower energy level to higher energy level in the conduction band.
2. electrons move from higher energy level to lower energy level in the conduction band.
3. holes in the valence band move from higher energy level to lower energy level.
4. holes in the valence band move from lower energy level to higher energy level.

Consider an npn transistor with its base-emitter junction forward biased and collector base junction reverse biased. Which of the following statements are true?

1. Electrons crossover from emitter to collector.
2. Holes move from base to collector.
3. Electrons move from emitter to base.
4. Electrons from emitter move out of base without going to the collector.

Consider an npn transistor with its base-emitter junction forward biased and collector base junction reverse biased. Which of the following statements are true?

1. Electrons crossover from emitter to collector.
2. Holes move from base to collector.
3. Electrons move from emitter to base.
4. Electrons from emitter move out of base without going to the collector.

Figure shows the transfer characteristics of a base biased CE transistor. Which of the following statements are true?

At V_i = 0.4 V, transistor is in active state.

At V_i = 1 V, it can be used as an amplifier.

At V_i = 0.5 V, it can be used as a switch turned off.

At V_i = 2.5 V, it can be used as a switch turned on.

In the depletion region of a diode ______.

1. there are no mobile charges.
2. equal number of holes and electrons exist, making the region neutral.
3. recombination of holes and electrons has taken place.
4. immobile charged ions exist.

The breakdown in a reverse biased p–n junction diode is more likely to occur due to ______.

1. large velocity of the minority charge carriers if the doping concentration is small.
2. large velocity of the minority charge carriers if the doping concentration is large.
3. strong electric field in a depletion region if the doping concentration is small.
4. strong electric field in the depletion region if the doping concentration is large.

Can the potential barrier across a p-n junction be measured by simply connecting a voltmeter across the junction?

(a)

(b)

1. Name the type of a diode whose characteristics are shown in figure (A) and figure (B).
2. What does the point P in figure (A) represent?
3. What does the points P and Q in figure (B) represent?