Alternating Current — Physics STD 12 Science — Question

To induce an e.m.f. in a coil, the linking magnetic flux

(a) Must decrease	(b) Can either increase or decrease
(c) Must remain constant	(d) Must increase

The potential gradient at which the dielectric of a condenser just gets punctured is called

(a) Dielectric constant

(b) Dielectric strength

(c) Dielectric resistance

(d) Dielectric number

Three bulbs of 40 W, 60 W, 100 W are arranged in series with 220 volt supply which bulb has minimum resistance

(a) 100 W

(b) 40 W

(c) 60 W

(d) Equal in all bulbs

A positive charge is moving vertically upwards in the magnetic field towards the south. In which direction will it be deflected?

Human eye:

Figure here shows P and Q as two equally intense coherent sources emitting radiations of wavelength 20 m. The separation PQ is 5.0 m and phase of P is ahead of the phase of Q by 90^o. A, B and C are three distant points of observation equidistant from the mid-point of PQ. The intensity of radiations at A, B, C will bear the ratio

(a) 0 : 1 : 4

(b) 4 : 1 : 0

(c) 0 : 1 : 2

(d) 2 : 1 : 0

If the atom   follows the Bohr model and the radius of   is n times the Bohr radius, then find n

(a) 100

(b) 200

(c) 4

(d)

The amplification factor of a triode is 20. If the grid potential is reduced by 0.2 volt then to keep the plate current constant its plate voltage is to be increased by

(a) 10 volt

(b) 4 volt

(c) 40 volt

(d) 100 volt

The electric potential V is given as a function of distance x (metre) by )volt. Value of electric field at x = 1  is

(a) 20 V/m

(b) 6 V/m

(c) 11 V/m

(d) -23 V/m