Electric Charges and Fields — Physics STD 12 Science — Question

A radioactive sample is a-emitter with half life 138.6 days is observed by a student to have 2000 disintegration/sec. The number of radioactive nuclei for given activity are

(a) 3.45 × 1010

(b) 1 × 1010

(c) 3.45 × 1015

(d) 2.75 × 1011

Fermi level of energy of an intrinsic semiconductor lies

(a) In the middle of forbidden gap	(b) Below the middle of forbidden gap
(c) Above the middle of forbidden gap	(d) Outside the forbidden gap

The magnitude of the electric field due to a point charge at a distance of 4.0 m is 9 N/C. Distance of this point charged substance due to electric field of magnitude 16 N/C will be:

Which of the following is a mechanical wave?

1. Radio waves.
2. X-rays.
3. Light waves.
4. Sound waves.

A parallel plate capacitor is charged from a battery and the battery is removed. Now if the distance between the plates of the capacitor is increased, then in the capacitor:

The electric potential at a point (x, y) in the  x - y  plane is given by V = -kxy. The field intensity at a distance r from the origin varies as

(a)

(b) r

(c)

(d)

The output current versus time curve of a rectifier is shown in the figure. The average value of the output current in this case is

(a) 0

(b) i0/p

(c) 2i0/p

(d) i0

Complete the reaction: 
₈₆​Rn²²⁰→₈₄​Po²¹⁶+ __________:

In the circuit given below, the value of the current is

(a) 0 amp

(b)  amp

(c)  amp

(d)  amp