Physics-1999-Set-III

(Only those questions have been answered, which are different from Set I and Set II)

Q6) What is the difference between voltage across an inductor & a capacitor in an a.c. circuit. (Marks 1)
Ans6) Voltage leads the current by /2 in an a.c circuit containing inductor & voltage lags the current by /2 in an a.c circuit containing capacitor.

Q7) Why are microwaves used in RADAR. (Marks 1)
Ans7) Microwaves are used in RADAR because they can be transmitted as beam signals in a particular direction. They donot spread or bend around the corners of an obstacle coming in their way.

Q9) What is self-induction? State any two factors on which the self inductance of a long solenoid depends. (Marks 2)
Ans9) Self induction is the property of a coil by virtue of which it opposes any change in the strength of current flowing through it by inducing an emf in itself.

Q10) Light from a distant galaxy having wavelength 6000 Ao is found to be shifted toward red by 60 Ao. Calculate the velocity of recession of the galaxy. (Marks 2)
Ans10) Given = 6000 Ao
d = 60 Ao
Now d/ = V/C
or V = dC/ = 60/6000 x 3 x 108 = 3 x 106 m/s

Q12) Draw a labelled ray diagram to show the image of an object in a compound microscope. (Marks 2)
Ans12) Ray diagram of image formation by compound microscope :

O : Objective
E : Eyepiece
AB : Object
A”B” : Final image
d : Least distance of distinct vision.

Q16) Briefly describe the method to determine the surface temp of sun. (Marks 2)
Ans16) Surface temperature of the sum can be determined by the knowledge of solar constant S. Solar constant is defined as the amount of radiant energy received per second by a unit area of a perfectly black body surface held at right angles to the direction of the sun rays at mean distance of earth from the sun. Its value is 1388 Wm-2
Consider sun to be a black body at temperature T and radius R at the centre of a hollow sphere of radius r
According to Stefan’s law E = T4
Total energy radiated per unit time by the sun
= 4R2E = 4R2T4
Solar luminousity = 4r2S
… 4R2T4 = 4r2S
or T = (r2S/R2)1/4
substituting the value of r, R, S &
T = [((1.496 x 1011)2 1288)/(6.928 x 108)2(5.735 x 10-8)]1/4
or T = 5800 K = 5,527oC

  1. No comments yet.
  1. No trackbacks yet.