Ray Optics and Optical Instruments — Physics STD 12 Science — Question

A magnet of magnetic moment  50   is placed along the x-axis in a magnetic field T. The torque acting on the magnet is

(a) 175

(b) 150

(c) 75

(d) 25

Four charges are placed on corners of a square as shown in figure having side of 5cm. If Q is one microcoulomb, then electric field intensity at centre will be

(a) 1.02  upwards	(b) 2.04  downwards
(c) 2.04  upwards	(d) 1.02  downwards

The direction of induced current is such that it opposes the very cause that has produced it. This is the law of

(a) Lenz

(b) Faraday

(c) Kirchhoff

(d) Fleming

Keeping the number of moles, volume and temperature the same, which of the following are the same for all ideal gases?

1. Rms speed of a molecule.
2. Density.
3. Pressure.
4. Average magnitude of momentum.

If there had been one eye of the man, then

(a) Image of the object would have been inverted	(b) Visible region would have decreased
(c) Image would have not been seen three dimensional	(d) (b) and (c) both

A 100% efficient transformer has 100 turns in the primary and 25 turns in its secondary coil. If the current in the secondary coil is 4 amp, then the current in the primary coil is

(a) 1 amp

(b) 4 amp

(c) 8 amp

(d) 16 amp

When a point source of light is at a distance of one metre from a photo cell, the cut off voltage is found to be V. If the same source is placed at 2 m distance from photo cell, the cut off voltage will be

(a) V

(b) V/2

(c) V/4

(d) V/

A plano-convex lens of refractive index 1.5 and radius of curvature 30 cm is silvered at the curved surface. Now this lens has been used to form the image of an object. At what distance from this lens an object be placed in order to have a real image of the size of the object

(a) 20 cm

(b) 30 cm

(c) 60 cm

(d) 80 cm

In water voltameter, the electrolysis of ...... takes place

(a)

(b)

(c)  and   both

(d)  and

A current of 1 ampere is passed through a straight wire of length 2.0 metres. The magnetic field at a point in air at a distance of 3 metres from either end of wire and lying on the axis of wire will be

(a)

(b)

(c)

(d) Zero