Science (English Medium) कक्षा १२ - CBSE Question Bank Solutions for Physics

We have stimulated emission and spontaneous emission. Do we also have stimulated absorption and spontaneous absorption?

An atom is in its excited state. Does the probability of its coming to ground state depend on whether the radiation is already present or not? If yes, does it also depend on the wavelength of the radiation present?

Three photons coming from excited atomic-hydrogen sample are picked up. Their energies are 12.1 eV, 10.2 eV and 1.9 eV. These photons must come from

The energy of an atom (or ion) in its ground state is −54.4 eV. It may be

A hot gas emits radiation of wavelengths 46.0 nm, 82.8 nm and 103.5 nm only. Assume that the atoms have only two excited states and the difference between consecutive energy levels decreases as energy is increased. Taking the energy of the highest energy state to be zero, find the energies of the ground state and the first excited state.

The mass number of a nucleus is

Potassium-40 can decay in three modes. It can decay by β⁻-emission, B*-emission of electron capture. (a) Write the equations showing the end products. (b) Find the Q-values in each of the three cases. Atomic masses of `""_18^40Ar` , `""_19^40K` and `""_20^40Ca` are 39.9624 u, 39.9640 u and 39.9626 u respectively.

(Use Mass of proton m_p = 1.007276 u, Mass of `""_1^1"H"` atom = 1.007825 u, Mass of neutron m_n = 1.008665 u, Mass of electron = 0.0005486 u ≈ 511 keV/c²,1 u = 931 MeV/c².)

Why is conducting easier in gases if the pressure is low? Will the conduction continue to improve if the pressure is made as low as nearly zero?

A triode is operated in the linear region of its characteristics. If the plate voltage is slightly increased, the dynamic plate resistance will __________ .

The plate current in a triode value is maximum when the potential of the grid is ______________ .

Electric conduction takes place in a discharge tube due to the movement of _____________ .
(a) positive ions
(b) negative ions
(c) electrons
(d) protons

Due to the space charge in a diode valve, _____________ .

The plate current in a diode is zero. It is possible that _____________ .

(a) the plate voltage is zero
(b) the plate voltage is slightly negative
(c) the plate voltage is slightly positive
(d) the temperature of the filament is low

The plate current in a triode valve is zero. The temperature of the filament is high. It is possible that ____________ .

(a) V_g > 0, V_p > 0
(b) V_g > 0, V_p < 0
(c) V_g < 0, V_p > 0
(d) V_g < 0, V_p < 0

The plate current in a triode can be written as \[i_p  = k \left( V_g + \frac{V_p}{\mu} \right)^{3/2}\] Show that the mutual conductance is proportional to the cube root of the plate current.

An a-particle and a proton of the same kinetic energy are in turn allowed to pass through a magnetic field `vec"B"`, acting normal to the direction of motion of the particles. Calculate the ratio of radii of the circular paths described by them.

Differentiate between amplitude modulated (AM) and frequency modulated (FM) waves by drawing suitable diagrams. Why is FM signal preferred over AM signal?

A 100 Ω resistor is connected to a 220 V, 50 Hz ac supply.

1. What is the rms value of current in the circuit?
2. What is the net power consumed over a full cycle?

A 100 Ω resistor is connected to a 220 V, 50 Hz ac supply.

What is the net power consumed over a full cycle?