Electrostatic Potential and Capacitance — Physics STD 12 Science — Question

A magnet is suspended in the magnetic meridian with an untwisted wire. The upper end of wire is rotated through 180^o to deflect the magnet by 30^o from magnetic meridian. When this magnet is replaced by another magnet, the upper end of wire is rotated through 270^o to deflect the magnet 30^o from magnetic meridian. The ratio of magnetic moments of magnets is

(a) 1 : 5

(b) 1 : 8

(c) 5 : 8

(d) 8 : 5

A point source of light is placed at a distance, of 2f from a converging lens of focal length f. The intensity on the other side of the lens is maximum at a distance:

1. f
2. between f and 2
3. 2f
4. more than 2f.

The ratio of thermionic currents (I/I₀) for a metal when the temperature is slowly increased  to T as shown in figure. (I and I₀ are currents at T and respectively). Then which one is correct?

(a) A

(b) B

(c) C

(d) D

Alternating current is produced in:

What will be the angular momentum of a electron, if energy of this electron in H-atom is 1.5eV (in J-sec)

(a) 1.05

(b) 2.1

(c) 3.15

(d) -2.1

The magnetic moment of a current (l) carrying circular coil of radius (r) and number of turns (n) varies as

From the following equations, pick out the possible nuclear reactions

(a)

(b)

(c)

(d)

When light propagates in vacuum there is an electric field and a magnetic field. These fields:

1. Are constant in time.
2. Have zero average value.
3. Are perpendicular to the direction of propagation of light.
4. Are mutually perpendicular.

The half-life of radioactive Polonium (Po) is 138.6 days. For ten lakh Polonium atoms, the number of disintegrations in 24 hours is

(a) 2000

(b) 3000

(c) 4000

(d) 5000

In the experiment of diffraction at a single slit, if the slit width is decreased, the width of the central maximum

(a) Increases in both Fresnel and Fraunhofer diffraction

(b) Decreases both in Fresnal and Fraunhofer diffraction

(c) Increases in Fresnel diffraction but decreases in Fraunhofer diffraction

(d) Decreases in Fresnel diffraction but increases is Fraunofer diffraction.