Atoms — Physics STD 12 Science — Question

The formula for induced e.m.f. in a coil due to change in magnetic flux through the coil is (here A = area of the coil, B = magnetic field)

(a) e = - A.

(b) e = -B.

(c) e = -

(d) e = -)

................. gave the principle of Electromagnetic Induction.

Heavy water is used as moderator in a nuclear reactor. The function of the moderator is

(a) To control the energy released in the reactor

(b) To absorb neutrons and stop chain reaction

(c) To cool the reactor faster

(d) To slow down the neutrons to thermal energies

Two waves having intensity in the ratio 25 : 4 produce interference. The ratio of the maximum to the minimum intensity is

(a) 5 : 2

(b) 7 : 3

(c) 49 : 9

(d) 9 : 49

A potentiometer has uniform potential gradient. The specific resistance of the material of the potentiometer wire is 10^–7 ohm–meter and the current passing through it is 0.1 ampere; cross-section of the wire is 10^–6 m².  The potential gradient along the potentiometer wire is

(a)  V/m

(b)   V/m

(c)  V/m

(d)  V/m

The maximum kinetic energy of a photo electron emitted from a metal is 1.8 eV . The value of stopping potential (cut-off voltage) will be :

When the particle and its anti-particle unite, the result is:

Three capacitors each of capacitance 1μF are connected in parallel. To this combination, a fourth capacitor of capacitance 1μF  is connected in series. The resultant capacitance of the system is

(a) 4μF

(b) 2μF

(c)

(d)

A sonometer wire of length l vibrates in fundamental mode when excited by a tuning fork of frequency 416Hz. If the length is doubled keeping other things same, the string will:

1. Vibrate with a frequency of 416Hz
2. Vibrate with a frequency of 208Hz
3. Vibrate with a frequency of 832Hz
4. Stop vibrating.