Wave Optics — Physics STD 12 Science — Question

If 20 gm of a radioactive substance due to radioactive decay reduces to 10 gm in  4 minutes, then in what time 80 gm of the same substance will reduce to 10 gm

(a) In 8 minutes

(b) In 12 minutes

(c) In 16 minutes

(d) In 20 minutes

Let  and  be the number of holes and conduction electrons respectively in a semiconductor. Then

(a)  in an intrinsic semiconductor

(b)  in an extrinsic semiconductor

(c)  in an intrinsic semiconductor

(d)  in an intrinsic semiconductor

If the distance between the plates of parallel plate capacitor is halved and the dielectric constant of dielectric is doubled, then its capacity will

(a) Increase by 16 times	(b) Increase by 4 times
(c) Increase by 2 times	(d) Remain the same

The photoelectric threshold wavelength for a metal surface is 6600 Å. The work function for this is

(a) 1.87 V

(b) 1.87 eV

(c) 18.7 eV

(d) 0.18 eV

The charge on proton is:

An average induced e.m.f. of 1V appears in a coil when the current in it is changed from 10A in one direction to 10 A in opposite direction in 0.5 sec. Self-inductance of the coil is

(a) 25 mH

(b) 50 mH

(c) 75 mH

(d) 100 mH

Let F_pp' F_pn and F_nn fill denote the magnitudes of the nuclear force by a proton on a proton, by a proton on a neutron and by a neutron on a neutron respectively. When the separation is 1fm:

In a junction diode, the holes are due to

(a) Protons

(b) Neutrons

(c) Extra electrons

(d) Missing of electrons

If a wire of length 1 meter placed in uniform magnetic field 1.5 Tesla at angle 30° with magnetic field. The current in a wire 10 amp. Then force on a wire will be

(a) 7.5 N

(b) 1.5 N

(c) 0.5 N

(d) 2.5 N