Moving Charges and Magnetism — Physics STD 12 Science — Question

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

Dynamo is a device for converting(a) Electrical energy into mechanical energy(b) Mechanical energy into electrical energy(c) Chemical energy into mechanical energy(d) Mechanical energy into chemical energy

A varying current in a coil change from 10A to 0 in 0.5sec. If the average emf induced in the coil is 220V, the self inductance of the coil is:

In producing a pure spectrum, the incident light is passed through a narrow slit placed in the focal plane of an achromatic lens because a narrow slit:

1. Produces less diffraction.
2. Increases intensity.
3. Allows only one colour at a time.
4. Allows a more parallel beam when it passes through the lens.

The graph shows the variation of magnetic field (B)with distance (r) from a long current carrying wire is-

The magnetic moment of a circular coil carrying current is:

Two electric charges 12μC and -6 μC  are placed 20 cm apart in air. There will be a point P on the line joining these charges and outside the region between them, at which the electric potential is zero. The distance of P from -6 μC  charge is (a) 0.10 m(b) 0.15 m(c) 0.20 m(d) 0.25 m

X – rays and γ -  rays of the same energies may be distinguished by(a) Their velocity(b) Their ionising power(c) Their intensity(d) Method of production

The time period of a freely suspended magnet is 4 seconds. If it is broken in length into two equal parts and one part is suspended in the same way, then its time period will be(a) 4 sec (b) 2 sec(c) 0.5 sec(d) 0.25 sec

Assertion  :   The lightening conductor at the top of high building has sharp pointed ends.
Reason     : The surface density of charge at sharp points is very high resulting in setting up of electric wind.(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.(c) If assertion is true but reason is false.(d) If the assertion and reason both are false.