Alternating Current — Physics STD 12 Science — Question

The magnetic induction at any point due to a long straight wire carrying a current is

(a) Proportional to the distance from the wire

(b) Inversely proportional to the distance from wire

(c) Inversely proportional to the square of the distance from the wire

(d) Does not depend on distance

The spectral series of the hydrogen spectrum that lies in the ultraviolet region is the

(a) Balmer series

(b) Pfund series

(c) Paschen series

(d) Lyman series

Four charges are arranged at the corners of a square ABCD, as shown in the adjoining figure. The force on the charge kept at the centre O is

(a) Zero	(b) Along the diagonal AC
(c) Along the diagonal BD	(d) Perpendicular to side AB

Whenever the magnetic flux linked with a coil changes, an induced e.m.f. is produced in the circuit. The e.m.f. lasts

Photoelectric effect shows:

A plane wavefront (λ = 6   falls on a slit 0.4 mm  wide. A convex lens of focal length 0.8 m  placed behind the slit focusses the light on a screen. What is the linear diameter of second maximum

(a) 6mm

(b) 12 mm

(c) 3 mm

(d) 9 mm

A wire of radius r has resistance R.  If it is stretched to a radius of  , its resistance becomes

(a)

(b)

(c)

(d)

Heat produced in a wire of resistance R due to current flowing at constant potential difference is proportional to

(a)

(b)

(c) R

(d)

A barometer kept in an elevator accelerating upward reads 76cm. The air pressure in the elevator is

1. 76cm.
2. < 76cm.
3. > 76cm.
4. zero.

The AC voltage across a resistance can be measured using: