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MHT-CET : Physics Entrance Exam

MHT - CET : Physics - Electrons and Photons Formulae Page 1

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1.

 

Force acting on a charged particle in an electric field

 

E

is given by

 

 

=

 q 

F

E

Where q = charge on the particle.

Let e be magnitude of charge on an electron;

 

when an electron is placed in an electric field

 

E

 

2.

 

The force acting on a charged particle in a magnetic field of intensity

 

B

 

by

 

 

 

|

|

= q v B sin q

F

 

Where q = angle between

 and 

v

B

 

 

= velocity of the particle.

v

 

If the magnetic field acts in a perpendicular direction, the particle undergoes a circular motion. The centripetal force is provided by the magnetic force.

mv2

 = q v B

r

(q = 90, sin q = 1)
Where
r = radius of the particle's circular path.
If the charged particle is an electron,

mv2

 = e v B

r

 

and r =

mv

e B

Where e = magnitude of the charge on the electron.

 

3.

 

Electric and magnetic fields act simultaneously on an electron in a mutually perpendicular direction. The direction and magnitude of the forces due to these fields are such that they nullify each other then,

v = 

Where v = velocity of electron
          E = intensity of electric field
          B = intensity of magnetic field

 

 4.

 

When a charged particle is accelerated from rest through a potential difference V, the increase in kinetic energy of the particle is given by

1

 mv2 = q V

2

 

5.

 

 

Energy of a photon is given by
E =
hv
Where
h = Plank's constant
n = frequency of radiation

n =  

C

l

 

\ E =

hc

l

Where c = velocity of electromagnetic radiation
          
l = wavelength of radiation

 

6.

 

Einstein's photoelectric equation: hn - W0 =

 

m (vmax)2

 

\ hn =  

1

 m (vmax)2+w0

2

Where hn = energy of photon of incident radiation

1

 m(Vmax)2= maximum kinetic energy of emitted photoelectrons

2

             W0 = work function of the emitting metal.

 

7.

 

e Vs =

m (vmax)2

Where e = charge on electron
          Vs = stopping potential

1

m (vmax)2 = maximum kinetic energy of photoelectrons

2

               m = mass of photoelectrons
               Vmax = maximum velocity of photoelectrons

 

8.

 

W0 = hn0

h c

l

Where W0  = work function of metal
             
h  = Plank's constant
           
n0  = threshold frequency
           
l0  = threshold wavelength
            C  = velocity of light / electromagnetic radiation.

 

9.

 

hn - hn0 = (K.E.)max

h c  

(

1

l

 - 

1

l0

)

 = (K.E.)max

 

\ h c 

(

l0 - l

l0l

)

= (K.E.)max

 

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