Question

Describe hertz and lenard's experiment to demonstrate photoelectric effect.

Answer 1

Photoelectric effect was discovered by Hertz in 1887 while performing an

experiment for production of electromagnetic waves by means of spark

discharge.

His observation was that sparks were more rapid in the air gap of the

transmitter if ultraviolet rays were directed at one of the metal plates but he

could not explain his observations.

Later it was concluded that this was caused by emission of electron from the

metal plate due to incidence of high frequency light.

Lenard observed that when uv radiations were incident  on the emitter plate

of an evacuated glass tubes enclosing electrodes current flows however

when radiation is stopped  flow of current also stops .

This shows that when uv fall on the  emitter plate (cathode) electrons are

ejected  which are attracted to the anode this flow completes the circuit and

current flows .

Answer 2

Answer:

Hertz and Lenards observation

In 1887 by Heinrich Hertz observed that when light falls on a metal surface, some electrons near the surface absorb enough energy from the incident radiation to overcome the attraction of the positive ions in the material of the surface. After gaining sufficient energy from the incident light, the electrons escape from the surface of the metal into the surrounding space.

In 1902, Lenard observed that the kinetic energy of electrons emitted increased with the frequency of radiation used. This could not be explained as Maxwell’s electromagnetic theory (which Hertz proved correct) predicted that the kinetic energy should be only dependent on light intensity (not frequency).