Wave Optics — Physics STD 12 Science — Question

A convex lens of focal length 25 cm and a concave lens of focal length 10 cm are joined together.  The power of the combination will be

(a) – 16 D

(b) + 16 D

(c) – 6 D

(d) + 6 D

In a triode amplifier, the value of maximum gain is equal to

(a) Half the amplification factor	(b) Amplification factor
(c) Twice the amplification factor	(d) Infinity

Artificial radioactivity was discovered by:

The amplification factor of a triode valve is 15. If the grid voltage is changed by 0.3 volt the change in plate voltage in order to keep the plate current constant (in volt) is

(a) 0.02

(b) 0.002

(c) 4.5

(d) 5.0

A person is in a room whose ceiling and two adjacent walls are mirrors. How many images are formed

(a) 5

(b) 6

(c) 7

(d) 8

Ampere’s circuital law states that:

When an electron strikes the target in a Coolidge tube, its entire kinetic energy:

1. Is converted into a photon.
2. May be converted into a photon.
3. Is converted into heat.
4. May be converted into heat.

PQRS is a square loop made of uniform conducting wire the current enters the loop at P and leaves at S.  Then the magnetic field will be

(a) Maximum at the centre of the loop	(b) Zero at the centre of loop
(c) Zero at all points inside the loop	(d) Zero at all points outside of the loop

An ammeter of 5 ohm resistance can read 5 mA. If it is to be used to read 100 volts, how much resistance is to be connected in series

(a) 19.9995 Ω

(b) 199.995 Ω

(c) 1999.95 Ω

(d) 19995 Ω

The current in a simple series circuit is 5.0 amp. When an additional resistance of 2.0 ohms is inserted, the current drops to 4.0 amp. The original resistance of the circuit in ohms was

(a) 1.25

(b) 8

(c) 10

(d) 20