# Physics-1996-Set II

**[Only those questions and answers which are different from set 1 have been given here.]**

**Q.1.If a rate of change of current of 4 A/s induces an e.m.f. of 20 mV in a solenoid, what is the self-inductance of the solenoid ? (1 mark)**

Ans 1.

…………….. dI = 4A/S

…………… …….dt

…………… ……. = 20mv = 20 x 10-3 V

…………… ……. | | = LdI

…………… ……………….dt

20 x 10-3 = L x 4 or L = 20 x 10-3 = 5 x10-3 H

…………… …………………. …………… 4

**Q 4. What is the work done in moving a charge of 20 nC between two points on an equipotential surface ? (1 mark)**

Ans 4. The work done in moving a change zone between two points on equipotential service is zero work done = q dv

…………… …dv = 0

…….work done = 0

**Q 5. Two stars A and B have magnitudes +1 and -1 respectively. Which of these two appears brighter? (1 mark)**

Ans 5. More negative the magnitude,brighter is the star. Hence B is brighter than A.

**Q 6. Define transconductance of a transistor. (1mark)**

Ans 6. Transconductance of a transistor is the ratio of change in collector current to the corresponding change in base-emitter voltage.

**Q 7. Which of the following has the shortest wavelength : microwaves,ultra-violet rays X-rays ? (1 mark)**

Ans 7. X-rays have the shortest wave-length among the three given wavelengths.