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

Which of the following are electromagnetic waves?

Suppose Swarglok (heaven) is in constant motion at a speed of 0.9999c with respect to the earth. According to the earth's frame, how much time passes on the earth before one day passes on Swarglok?

If a person lives on the average 100 years in his rest frame, how long does he live in the earth frame if he spends all his life on a spaceship going at 60% of the speed of light.

When the diode shows saturated current, dynamic place resistance is _____________ .

Electric charges are distributed in a small volume. The flux of the electric field through a spherical surface of radius 10 cm surrounding the total charge is 25 V m. The flux over a concentric sphere of radius 20 cm will be _____________ .

Answer the following question.
When an inductor is connected to a 200 V dc voltage, a current at 1A flows through it. When the same inductor is connected to a 200 V, 50 Hz ac source, only 0.5 A current flows. Explain, why? Also, calculate the self-inductance of the inductor. 

Show that the time period (T) of oscillations of a freely suspended magnetic dipole of magnetic moment (m) in a uniform magnetic field (B) is given by `"T" = 2pi sqrt("I"/"mB")`, where I is a moment of inertia of the magnetic dipole.

A variable resistor R is connected across a cell of emf ε and internal resistance r as shown in the figure. Draw a plot showing the variation of
(i) Terminal voltage V and
(ii) the current I, as a function of R.

The electric flux through a closed Gaussian surface depends upon ______.

The ability of a junction diode to ______ an alternating voltage is based on the fact that it allows current to pass only when it is forward biased.

Obtain the resonant frequency ω_r of a series LCR circuit with L = 2.0 H, C = 32 µF and R = 10 Ω. What is the Q-value of this circuit?

The wires which connect the battery of an automobile to its starting motor carry a current of 300 A (for a short time). What is the force per unit length between the wires if they are 70 cm long and 1.5 cm apart? Is the force attractive or repulsive?

A straight wire of diameter 0.5 mm carrying a current of 1 A is replaced by another wire of 1 mm diameter carrying the same current. The strength of the magnetic field far away is ______.

The frequency of γ-rays, X-rays and ultraviolet rays are a, b and c respectively. Then, ______.

In interaction of radiation with matter, radiation behaves as if it is made up of particles called ______.

The electric flux through the surface ______.

(i)	(ii)	(iii)	(iv)