Ray Optics and Optical Instruments — Physics STD 12 Science — Question

Assertion  : Microwave propagation is better than the sky wave propagation.

Reason      :  Microwaves have frequencies 100 to 300 GHz, which have very good directional properties.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

In forward bias, the width of potential barrier in a P-N junction diode

(a) Increases	(b) Decreases
(c) Remains constant	(d) First increases then decreases

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

The peak value of voltage of an A.C. circuit is 440 V. Its virtual voltage is :

A capacitor of capacity  is charged upto V volt and then connected to an uncharged capacitor of capacity  . Then final potential difference across each will be

(a)

(b)

(c)

(d)

The truth table given in figure represents:

A	B	Y
0	0	0
0	1	1
1	0	1
1	1	1

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

What is the nature of equipotential surfaces in case of a positive point charge?

The time period of a particle in simple harmonic motion is equal to the time between consecutive appearances of the particle at a particular point in its motion. This point is:

1. The mean position.
2. An extreme position.
3. Between the mean position and the positive extreme.
4. Between the mean position and the negative extreme.

Atomic mass of an element is: