Alternating Current — Physics STD 12 Science — Question

Cyclotron is a device used to _________.

Let i_E, i_C and i_B represent the emitter current, the collector current and the base current respectively in a transistor. Then,

1. i_C is slightly smaller than i_E.
2. i_C is slightly greater than i_E.
3. i_B is much smaller than i_E.
4. i_B is much greater than i_E.

In producing a pure spectrum, the incident light is passed through a narrow slit placed in the focal plane of an achromatic lens because a narrow slit:

1. Produces less diffraction.
2. Increases intensity.
3. Allows only one colour at a time.
4. Allows a more parallel beam when it passes through the lens.

A medium is said to be dispersive, if

(a) Light of different wavelengths propagate at different speeds

(b) Light of different wavelengths propagate at same speed but has different frequencies

(c) Light is gradually bent rather than sharply refracted at an interface between the medium and air

(d) Light is never totally internally reflected

The molecules in which centres of positive and negative charges are separated are called as:

Two capacitors of capacitances 3 μF  and 6 μF  are charged to a potential of 12 V each. They are now connected to each other, with the positive plate of each joined to the negative plate of the other. The potential difference across each will be

(a) 6 volt

(b) 4 volt

(c) 3 volt

(d) Zero

In a capacitor of capacitance 20 μF, the distance between the plates is 2mm. If a dielectric slab of width 1mm and dielectric constant 2 is inserted between the plates, then the new capacitance is

(a) 2 μF

(b) 15.5 μF

(c) 26.6 μF

(d) 32 μF

In an atomic bomb, the energy is released due to

(a) Chain reaction of neutrons and

(b) Chain reaction of neutrons and

(c) Chain reaction of neutrons and

(d) Chain reaction of neutrons and

On giving 220V to a resistor the power dissipated is 40W then value of resistance is

(a) 1210 W

(b) 2000 W

(c) 1000 W

(d) None of these