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 = C l

 \ E = hc l

Where c = velocity of electromagnetic 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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