Physics-1996-Set I

Q 1. What is the work done in moving a charge of 10 nC between two points on an equipotential surface ? (1 mark)
Ans 1. dw = qdv
on equipotential surface dv = 0

dw = 0 i.e,no work is done in moving a change on an equipotential surface.

Q 2. Name the device used for measuring the internal resistance of a secondary cell ? (1 mark)
Ans 2. Internal resistance of a secondary cell can be measured by a potentiometer.

Q 3. What is the nature of magnetic field in a moving coil galvanometer ? (1 mark)
Ans 3. A radial magnetic fields exists in a moving coil galvanometer.

Q 4.If a rate of change of current of 2 A/s induces an e.m.f.of 10mV in a solenoid, what is the self -inductance of the solenoid ? (1 mark)

Ans 4. Given dI = 2 A/S , 10mv = 10-3V
dt
| | = L dI
dt

or 10 x 10

-3 = L x 2

or L = 10-2 = 5 x 10-3 H = 5mH
2

Q 5. What type of magnetic material is used in making permanent magnets ? (1 mark)
Ans 5. A substance like steel which as a large retentivity and a large coercivity is used in making permanent magnets.

Q 6. Two metals A, B have work-functions 2eV, 4eV respectively. Which metal has lower threshold wavelength for photoelectric effect ? (1 mark)
Ans 6. Work function W = h v

0 = hc where is threshold wavelength.

x 1
W
Metal B has higher value of W & hence lower threshold wavelength.

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