# 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