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

Two source S₁ and S₂ of intensity I₁ and I₂ are placed in front of a screen [Figure (a)]. The pattern of intensity distribution seen in the central portion is given by Figure (b).

(a)

(b)

1. S₁ and S₂ have the same intensities.
2. S₁ and S₂ have a constant phase difference.
3. S₁ and S₂ have the same phase.
4. S₁ and S₂ have the same wavelength.

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.

A message signal of frequency ω_m is superposed on a carrier wave of frequency ω_c to get an amplitude modulated wave (AM). The frequency of the AM wave will be ______.

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.

Identify the mathematical expression for amplitude modulated wave ______.

In amplitude modulation, the modulation index m, is kept less than or equal to 1 because ______.

1. m > 1, will result in interference between carrier frequency and message frequency, resulting into distortion.
2. m > 1 will result in overlapping of both side bands resulting into loss of information.
3. m > 1 will result in change in phase between carrier signal and message signal.
4. m > 1 indicates amplitude of message signal greater than amplitude of carrier signal resulting into distortion.

The maximum amplitude of an A.M. wave is found to be 15 V while its minimum amplitude is found to be 3 V. What is the modulation index?

Compute the LC product of a tuned amplifier circuit required to generate a carrier wave of 1 MHz for amplitude modulation.

Why is a AM signal likely to be more noisy than a FM signal upon transmission through a channel?

On radiating (sending out) an AM modulated signal, the total radiated power is due to energy carried by ω_c, ω_c – ωm and ω_c + ω_m. Suggest ways to minimise cost of radiation without compromising on information.

An amplitude modulated wave is as shown in figure. Calculate

1. the percentage modulation
2. peak carrier voltage and
3. peak value of information voltage.

Draw the plot of amplitude versus ‘ω’ for an amplitude modulated wave whose carrier wave (ω_c) is carrying two modulating signals, ω₁ and ω₂ (ω₂ > ω₁). 

1. Is the plot symmetrical about ωc? Comment especially about plot in region ω < ωc.
2. Extrapolate and predict the problems one can expect if more waves are to be modulated.
3. Suggest solutions to the above problem. In the process can one understand another advantage of modulation in terms of bandwidth?

A hydrogen atom makes a transition from n = 5 to n = 1 orbit. The wavelength of photon emitted is λ. The wavelength of photon emitted when it makes a transition from n = 5 to n = 2 orbit is ______.

The formation of the depletion region in a p-n junction diode is due to ______.

Define the critical angle for a given pair of media and total internal reflection. Obtain the relation between the critical angle and refractive index of the medium.

A point object in the air is placed symmetrically at a distance of 60 cm in front of a concave spherical surface with a refractive index of 1.5. If the radius of curvature of the surface is 20 cm, find the position of the image formed.

A series RL circuit with R = 10 Ω and L = `(100/pi)` mH is connected to an ac source of voltage V = 141 sin (100 πt), where V is in volts and t is in seconds. Calculate

1. the impedance of the circuit
2. phase angle, and
3. the voltage drop across the inductor.

During the formation of a p-n junction ______.