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

Temperature dependence of resistivity ρ(T) of semiconductors, insulators and metals is significantly based on the following factors:

1. number of charge carriers can change with temperature T.
2. time interval between two successive collisions can depend on T.
3. length of material can be a function of T.
4. mass of carriers is a function of T.

Two identical current carrying coaxial loops, carry current I in an opposite sense. A simple amperian loop passes through both of them once. Calling the loop as C ______.

1. `oint B.dl = +- 2μ_0I`
2. the value of `oint B.dl` is independent of sense of C.
3. there may be a point on C where B and dl are perpendicular.
4. B vanishes everywhere on C.

The self inductance L of a solenoid of length l and area of cross-section A, with a fixed number of turns N increases as ______.

Consider an infinitely long wire carrying a current I(t), with `(dI)/(dt) = λ` = constant. Find the current produced in the rectangular loop of wire ABCD if its resistance is R (Figure).

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.

Photons absorbed in matter are converted to heat. A source emitting n photon/sec of frequency ν is used to convert 1 kg of ice at 0°C to water at 0°C. Then, the time T taken for the conversion ______.

1. decreases with increasing n, with ν fixed.
2. decreases with n fixed, ν increasing.
3. remains constant with n and ν changing such that n ν = constant.
4. increases when the product n ν increases.

There are two sources of light, each emitting with a power of 100 W. One emits X-rays of wavelength 1 nm and the other visible light at 500 nm. Find the ratio of number of photons of X-rays to the photons of visible light of the given wavelength?

Which one of the following cannot emit radiation and why? Excited nucleus, excited electron.

In pair annihilation, an electron and a positron destroy each other to produce gamma radiation. How is the momentum conserved?

A 220 V A.C. supply is connected between points A and B (figure). What will be the potential difference V across the capacitor?

The output of the given circuit in figure is given below.

To reduce the ripples in a rectifier circuit with capacitor filter ______.

1. R_L should be increased.
2. input frequency should be decreased.
3. input frequency should be increased.
4. capacitors with high capacitance should be used.

Draw the output waveform across the resistor (Figure).

Assuming the ideal diode, draw the output waveform for the circuit given in figure. Explain the waveform.

The temperature (T) dependence of resistivity of materials A and material B is represented by fig (i) and fig (ii) respectively. Identify material A and material B.

fig. (i)

fig. (ii)

Two concentric and coplanar circular loops P and Q have their radii in the ratio 2:3. Loop Q carries a current 9 A in the anticlockwise direction. For the magnetic field to be zero at the common centre, loop P must carry ______.

With the help of a circuit diagram, explain briefly how a p-n junction diode works as a half-wave rectifier.

Give two differences between a half-wave rectifier and a full-wave rectifier.

A long straight wire of radius 'a' carries a steady current 'I'. The current is uniformly distributed across its area of cross-section. The ratio of the magnitude of magnetic field `vecB_1` at `a/2` and `vecB_2` at distance 2a is ______.