Moving Charges and Magnetism — Physics STD 12 Science — Question

Magnetic fields at two points on the axis of a circular coil at a distance of 0.05m and 0.2m from the centre are in the ratio 8 : 1. The radius of the coil is(a) 1.0 m (b) 0.1 m(c) 0.15 m(d) 0.2 m

The focal lengths of convex lens for red and blue light are 100 cm and 96.8 cm respectively. The dispersive power of material of lens is(a) 0.325(b) 0.0325(c) 0.98   (d) 0.968

An electric lamp is marked 60 W, 230 V. The cost of a 1 kWh of energy is Rs. 1.25. The cost of using this lamp 8 hrs a day for 30 day is(a) Rs. 10 (b) Rs. 16(c) Rs. 18 (d) Rs. 20

What is the driving force in a working Electrical Circuit?

A convex lens of power + 6D is placed in contact with a concave lens of power – 4D.  What is the nature and focal length of the combination(a) Concave, 25 cm (b) Convex, 50 cm(c) Concave, 20 cm(d) Convex, 100 cm

A rectangular coil 20 cm × 20 cm  has 100 turns and carries a current of 1 A. It is placed in a uniform magnetic field       B  = 0.5 T with the direction of magnetic field parallel to the plane of the coil. The magnitude of the torque required to hold this coil in this position is(a) Zero  (b) 200 N-m(c) 2 N-m  (d) 10 N-m

The sum of all electromagnetic forces between different particles of a system of charged particles is zero:

1. Only if all the particles are positively charged.
2. Only if all the particles are negatively charged.
3. Only if half the particles are positively charged and half are negatively charged.
4. Irrespective of the signs of the charges.

Fusion reactions take lace at high temperature because:

An electric motor operates on a 50 volt supply and a current of 12A. If the efficiency of the motor is 30%, what is the resistance of the winding of the motor(a) 6 Ω(b) 4 Ω(c) 2.9 Ω(d) 3.1 Ω

A metal surface of work function 1.07 eV is irradiated with light of wavelength 332 nm. The retarding potential required to stop the escape of photo-electrons is(a) 4.81 eV(b) 3.74 eV(c) 2.66 eV(d) 1.07 eV