Wave Optics — Physics STD 12 Science — Question

Large transformers, when used for some time, become hot and are cooled by circulating oil. The heating of transformer is due to

(a) Heating effect of current alone

(b) Hysteresis loss alone

(c) Both the hysteresis loss and heating effect of current

(d) None of the above

The number of dry cells, each of e.m.f. 1.5 volt and internal resistance 0.5 ohm that must be joined in series with a resistance of 20 ohm so as to send a current of 0.6 ampere through the circuit is

(a) 2

(b) 8

(c) 10

(d) 12

The maximum current that flows through a fuse wire before it blows out varies with its radius as

(a)

(b) r

(c)

(d)

Charge is:

Two radioactive materials  and  have decay constants 10λ  and λ respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of   to that of   will be 1/e  after a time

(a) 1/(10 λ)

(b) 1/(11 λ)

(c) 11(10 λ)

(d) 1(9 λ)

The radio of deBroglie wavelengths of a proton and an alpha particle of same energy is:

The mass defect in a particular nuclear reaction is 0.3 grams. The amount of energy liberated in kilowatt hours is (Velocity of light = 3)

(a) 1.5

(b) 2.5

(c) 3

(d) 7.5

If the light moving in a straight line bends by a small but fixed angle, it may be a case of:

1. Reflection.
2. Refraction.
3. Diffraction.
4. Dispersion.

How does the red shift confirms that the universe is expanding

(a) Due to Wien's law	(b) Due to Stefan's law
(c) Due to Kirchhoff's law	(d) Due to Doppler's effect

The unit of intensity of electric field is

(a) Newton/Coulomb

(b) Joule/Coulomb

(c) Volt - metre

(d) Newton/metre