31.

Lenz's law of electromagnetic induction corresponds to the

• law of conservation of charge

• law of conservation of energy

• law of conservation of momentum

• law of conservation of angular momentum

A thin wire of resistance 4Ω is bent to form a circle. The resistance across any diameter is

• 4 Ω

• 2 Ω

• 1 Ω

• 8 Ω

A battery of e.m.f. E and internal resistance r is connected to an external resistance R the condition for maximum power transfer is

• r < R

• r > R

• r = 1/R

• r = R

The ionisation potential of hydrogen atom is -13.6 eV. An electron in the ground state of a hydrogen atoms absorbs a photon of energy 12.75 eV. How many different spectral line can one expect when the electron make a downward transition ?

• 1

• 4

• 2

• 6

The refractive indices of glass and quartz w.r.t. air are 3/2 and 12/5 respectively. The refractive index of quartz w.r.t. glass is

• 8/5

• 5/8

• 5/18

• 18/5

The radius of curvature of concave mirror is 24 cm and the image is magnified by 1.5 times. The object distance is

• 20 cm

• 8 cm

• 16 cm

• 24 cm

A point source of light is kept at a depth of h in water of refractive index 4/ 3. The radius of the circle at the surface of water through which light emits is

• $\frac{3}{\sqrt{7}} \mathrm{h}$

• $\frac{\sqrt{7}}{3} \mathrm{h}$

• $\frac{\sqrt{3}}{7} \mathrm{h}$

• $\frac{7}{\sqrt{3}} \mathrm{h}$

Which of the following statement is correct ?

• The rest mass of a stable nucleus is less than the sum of the rest masses of its separated nucleons.

• The rest mass of a stable nucleus is greater than the sum of the rest masses of its separated nucleons.

• In nuclear fission, energy is released by fusion two nuclei of medium mass (approximately 1O0 amu).

• In nuclear fission, energy is released by fragmentation of a very low nucleus.

A Si and a Ge diode has identical physical dimensions. The band gap in Si is larger than that in Ge. An identical reverse bias is applied across the diodes

• The reverse current in Ge is larger than that in Si

• The reverse current in Si is larger than that in Ge

• The reverse current is identical in the two diodes

• The relative magnitude of the reverse currents cannot be determined from the given data only

The binary number 10111 is equivalent to the decimal number

• 19

• 31

• 23

• 22