2019-03-01_Physics_Times

The possible answer is (b).

The minimum excitation energy of hydrogen

atom in ground state is 10. 2 eV. If the colliding

particle K.E is less than 10.2 eV then excitation does

not take place. So the K.E of the system is

conserved and hence collision is perfectly elastic.

Note: If K.E 10.2eV then excitation may take

place and hence some part of K.E is converted into

excitation energy. In this case collision is not

perfectly elastic.

In photoelectric effect, the energy of a photon

is transformed into the kinetic energy of a

photoelectron, while during X-ray emission the

kinetic energy of a photon is converted into X-rays.

n 3 to n 2

2 2

1 1 2

1 1 1

R

 n n

 

   

 

2 2

1

1 1 1

2 3

R

 

   

  

1

1 5

36

R

 

  

   (1)

2

1 1 1

9 25

R

 

   

  

2

1 16

9 25

R

 

  

    (2)

From (1) & (2)

2 1

5 9 25 125

36 16 64



    

Energy of emitted photon 2.6 eV

2

2 2

1 1

2.6 13.6

4

z

n

 

   

 

 

2

2 2

2.6 1 1

2 2

13.6 4

z

n

 

    

 

2

2.6 1 1

13.6 4 n 16

 



 n 3

2

2

13.6

t eV

Z

E

n





13.6 4

eV 6eV

9

Et

 

  

Self energy of a spherical sheel of radius R

and charge q is

2

(^80)
q
R
2
2
(^80)
e
e
m c
R


 R 1.4 10^15 m
Collision of e lead to excitation of molecules
So collision is inelastic since some part K.E is
converted into excitation energy.
 K K'
Momentum remain Conserved during collision.
P P '
 
Between nucleus and electron, first electrosta
tic attraction and then nuclear attraction are
present. The potential is negative so the correct
graph is (3).
Between nucleus and proton first electrostatic
repulsion and then nuclear attraction are present.
The potential is first positive and then negative so
the correct graph is (2).
Between nucleus and neutron there is no
electrostatic force and only nuclear attraction exists
at short distance. So the correct graph is (1).
For hydrogenic (hydrogen like) atoms the three
possible transitions are shown in the figure.
E E E 1   2 3
1 2 3
hc hc hc
 
  
4.Sol:
5.Sol:
6.Sol:
7.Sol:
8.Sol:
9.Sol:
10.Sol:
11.Sol:
Nuclear Physics
1.Sol:
1 2 3
1 1 1
 
  
The rate of decay is given by R R e 0 t
where R 0 is the intial activity and  is the rate
constant.