# Physics-1998-Set-II

** (Only those uestionshave been given here, which are different from set I )**

**Q6) Calculate rms value of alternating current in diagram.(Marks 1)**

Ans6) Irms = I2 = (1.52 + (-1.5)2 + 1.52) = 1.5A

**Q7) Two wires A and B are of the same metal and of the same length have their areas of cross-section in the ratio of 2 : 1. if the same potential difference is applied across each wire in turn, what will be the ratio of the currents flowing in A and B? (Marks 1)**

Ans7) Resistance is inversely proportional to area

RA/RB = AB/AA = 1/2

Now current is inversely proportional to resistance

… IA/IB = RB/RA = 2/1

**Q14) An electron in an atoms revolves around the nucleus in an orbit of radius 0.53 A. Calculate the equivalent magnetic moment if the frequency of revolution of electrons is 1010 MHz. (Marks 2)**

Ans14) Given r = 0.5A = 0.5 x 10-10m

= 1010 MHz = 1016 Hz

e = 1.6 x 10-19c

magnetic moment = eA = er2

= 1016 x 1.6 x 10-19 x 3.14 x (.5 x 10-10)2

= 1.256 x 10-23 Am2

**Q15) Describe the use of a vibration magnetometer for comparing magnetic moments of two bar magnets of same size and mass.
(Marks 2)**

Ans15) Let T1 & T2 be the time periods of vibration of two magnets at a place. Then

T1 = 2(I/M1H)

T2 = 2(I/M2)

or T1/T2 = (M2/M1)

or M2/M1 = T22/T12

**Q17) Draw a labelled diagram of Daniel cell. What is the function of copper sulphate and sulphuric acid solutions used in it? (Marks 2)**

Ans17) Daniel cell

Copper Sulphate acts as depolarizer

Sulphuric acid is electrolyte

**Q22) Draw a ray diagram to show formation of image by a refracting type astronomical telescope. On what factors does its (i) magnifying power and (ii) resolving power depend ? (Marks 3)**

Ans22) Refracting type Astronomical telescope:

Magnifying power depends on focal length of objective lens & eye lens.

Resolving power = D/1.22 . So it depends on

D : Diameter or the aperture of objective lens

: Wavelength of light used.