Alternating Current — Physics STD 12 Science — Question

The amplification factor of a triode is 50. If the grid potential is decreased by 0.20 V, what increase in plate potential will keep the plate current unchanged

(a) 5 V

(b) 10 V

(c) 0.2 V

(d) 50 V

In a vibration magnetometer, the time period of a bar magnet oscillating in horizontal component of earth's magnetic field is 2 sec. When a magnet is brought near and parallel to it, the time period reduces to 1 sec. The ratio H/F of the horizontal component H and the field F due to magnet will be

(a) 3

(b) 1/3

(c)

(d) 1/

Resistance of tungsten wire at 150℃  is 133 Ω . Its resistance temperature coefficient is 0.0045/℃. The resistance of this wire at 500 ℃  will be

(a) 180 Ω

(b) 225 Ω

(c) 258 Ω

(d) 317 Ω

An electron is projected along the axis of a circular conductor carrying some current. Electron will experience force

(a) Along the axis	(b) Perpendicular to the axis
(c) At an angle of 4o with axis	(d) No force experienced

The reason for shining of air bubble in water is

(a) Diffraction of light	(b) Dispersion of light
(c) Scattering of light	(d) Total internal reflection of light

The couple developed in the suspension wire and the loose spring in a suspension type of moving coil galvanometers called:

An alternating current having peak value 14A is used to heat a metal wire. To produce the same heating effect, a constant current i can be used where i is:

At a place, if the earth's horizontal and vertical components of magnetic fields are equal, then the angle of dip will be

(a) 30°

(b)  90°

(c) 45°

(d)  0°

The Balmer series for the H-atom can be observed: