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Force acting on a charged particle in an electric field
is given by
Where q = charge on the particle.
Let e be magnitude of charge on an electron;
when an electron is placed in an electric field
The force acting on a charged particle in a magnetic
field of intensity
= q v B sin q
Where q = angle between
= velocity of the particle.
If the magnetic field acts in a perpendicular direction,
the particle undergoes a circular motion. The centripetal force is
provided by the magnetic force.
= q v B
(q = 90°, sin q = 1)
Where r = radius of
the particle's circular path.
If the charged particle is an electron,
= e v B
and r =
Where e = magnitude of the charge on the electron.
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,
Where v = velocity of electron
intensity of electric field
intensity of magnetic field
When a charged particle is accelerated from rest through a
potential difference V, the increase in kinetic energy of the particle
is given by
mv2 = q V
Energy of a photon is given by
E = hv
Where h = Plank's
n = frequency of
\ E =
Where c = velocity of electromagnetic radiation
l = wavelength of
Einstein's photoelectric equation: hn - W0
\ hn =
Where hn = energy of photon of incident radiation
maximum kinetic energy of emitted photoelectrons
= work function of the emitting metal.
Where e = charge on electron
= stopping potential
m (vmax)2 = maximum kinetic
energy of photoelectrons
m = mass of
Vmax = maximum velocity of
W0 = hn0 =
= work function of metal
= velocity of light / electromagnetic radiation.
hn - hn0 = (K.E.)max
\ h c
l0 - l