History of Photoelectric Effect Video Lecture - Physics Class 12 - NEET

Albert Einstein in 1921 got the Nobel
Prize in Physics for his work on the
photoelectric effect but what is the
photoelectric effect the photoelectric
effect was first observed by Heinrich
Hertz in 1887 while he was working on
the spark gap generator in a spark gap
generator there are two metal spheres
and an electric spark travels from one
metal sphere to the another Hertz
observed that when the sphere of the
spark gap generator was illuminated with
visible or UV light the sensitivity of
the spark gap generator increased later
digitoxin discovered that the increased
sensitivity of the spark gap generator
was a result of the light pushing on the
electrons by pushing he meant that the
energy of light was transferred into the
electrons of the metal sphere which led
to the increase in sensitivity as the
electrons with more energy could now
travel longer distances an assistant of
Hertz Philipp Lenard later discovered
that the intensity of the light did not
have any effect on the maximum kinetic
energy of the electrons that were
emitted now for classical physics this
was counterintuitive imagine a set of
marbles on the ground a tornado comes
and the marbles are intact nothing
happens but just a slight breeze and
some marbles go away counterintuitive
right that was a reaction of the
physicists at that time so what was
going on well Einstein figured this out
he assumed that light is not continuous
like a breeze or a tornado it is
actually made up of discrete particles
known as quanta higher intensity of
light does not mean more number of
quanta it actually means more energetic
quanta so even if you shine bright
intense light on the metal surface the
number of photons or quanta still remain
the same and thus the intensity of light
had no effect on the emission of
electrons whatsoever
Einstein also concluded that each metal
has a threshold frequency that is the
minimum frequency of light that is
required for the electrons to be emitted
from the surface of the metal
consequently Einstein developed
equations and the mystery was solved at
last
but how does all this help us well it is
all around you the photoelectric
technology is now used in automatically
opening doors intrusion alarms exposure
meter in your camera solar panels and
many other places thanks to Einstein and
his fellow scientists thanks for
watching