Current Electricity — Physics STD 12 Science — Question

In case of Coulomb’s law, the value of k is given by:

If the source of light used in a Young's double slit experiment is changed from red to violet:

The amplification factor of a triode valve is 15. If the grid voltage is changed by 0.3 volt the change in plate voltage in order to keep the plate current constant (in volt) is

(a) 0.02

(b) 0.002

(c) 4.5

(d) 5.0

The electric field between the two spheres of a charged spherical condenser

(a) Is zero	(b) Is constant
(c) Increases with distance from the centre	(d) Decreases with distance from the centre

Carbon -14 decays with half-life of about 5,800 years. In a sample of bone, the ratio of carbon -14 to carbon -12 is found to be   of what it is in free air. This bone may belong to a period about x centuries ago, where x is nearest to

(a) 2 × 58

(b) 58

(c) 58/2

(d) 3 × 58

In a radioactive decay, neither the atomic number nor the mass number changes. Which of the following particles is emitted in the decay?

1. Proton.
2. Neutron.
3. Electron.
4. Photon.

n identical cells each of e.m.f. E and internal resistance r are connected in series. An external resistance R is connected in series to this combination. The current through R is

(a)

(b)

(c)

(d)

In the photoeletric effect, electrons are emitted:

An electric motor operating on a 60 V dc supply draws a current of 10 A. If the efficiency of the motor is 50%, the resistance of its winding is

(a) 3Ω

(b) 6 Ω

(c) 15 Ω

(d) 30 Ω

The refractive index of water is 1.33. The direction in which a man under water should look to see the setting sun is

(a) 49o to the horizontal	(b) 90o with the vertical
(c) 49o to the vertical	(d) Along the horizontal