Physics-1997-Set-II

Q1) Is the ratio of number of holes and the number of conduction electrons in a n-type extrinsic semiconductors more than, less than or equal to 1? (Marks 1)
Ans1) nh/ne in N type < 1 as holes are minority charge carriers & electrons are majority charge carriers.

Q9) Use mirror formula to show that a convex mirror always produces a virtual image independent of the location of the object. (Marks 2)

Ans9) According to mirror formula
1 / f = 1 / v + 1/u
For convex mirror f > 0 (being +) & u < 0 (being - ve)
1 / v = 1 / f - 1 / u = 1 / |f| + 1 / |u|
v is always +ve i.e. , image will be behind the mirror. Thus convex mirror always gives virtual & erect image.

Q10) An astronomical telescope of magnifying power 10 consists of two thin lenses 55 cm apart. Calculate the focal lengths of the lenses. (Marks 2)
Ans10) m = 10, L = 55 cm
m = fo/fe or fo = mfe
L = fo + fe = mfe + fe = (m + 1) fe
55 = (10 + 1) fe or fe = 5 cm
fo = 10 fe = 50 cm.

Q11) An -particle and a proton are accelerated through same potential differences. Calculate ratio of linear momentum acquired by the two. (Marks 2)
Ans11) Now qV = 1/2 mv2
For particle
(2e)V = 1/2 mv2 – (i)
For proton
(e)V = 1/2 mpvp2 – (ii)
Dividing (i) by (ii)
2 = mv2/mpvp2
m/mp = 4
=> v2/vp2 = 2 x 1/4 =1/2
or v/vp = 1/2
The ratio of linear momentum is
P/Pp = mv/mpvp = 4 x 1/2 = 22

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