2019-03-01_Physics_Times

2.

[2014]

3.

[2013]

A certain p-n junction, having a depletion region of
width 20 μm, was found to have a breakdown voltage
of 100 V. If the width of the depletion region is
reduced to 1 μm during its production, then it can
be used as a Zener diode for voltage regulation of

(a) 5 V (b) 10 V (c) 7.5 V (d) 2000 V

The figure below shows a circuit and its input

voltage vi as function of time t.

Assuming the diodes to be ideal, which of the

following graphs depict the output voltage v 0 as

function of time t?

(a) (b)

(c) (d)

a a b b d

b b a b a

d

b b b d a

a a a d c

d a a

Atomic structure and X-ray

Nuclear physics

Semiconductors

Atomic Structure and X-rays

1.Sol:

2.Sol:

3. Sol:

2

2 2 2 1

1 2

1 1 1

RZ ;n 2, 1n

 n n

 

     

 

2 7

4 4 4

2Å

3 RZ 2028 R 2028 1.09 10

    

 

2

h

mvr n





(^2)  
2
h
mr n v r

 
2
nh
r
 m

2
h
r n
 m

(^) r n a.
From conservation of angular momentum
2
h
mvr n

 (1)
Centripetal force on an electron is
2 2 2
(^2) (2 ) 2
mv ke ke
r r r
 
2 2
2
3
4
mv ke
r r

2 3 2
4
mv r ke (2)
From eq’s (1) & (2)
2
0
2
4 4
3
r
me

 

2
h

 
  
 

4
3 B
r a