Explain the experiment conducted by J J Thomson that led to the discovery of electrons.
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Solution
J J Thomson conducted an experiment to see how the gases conduct an electric current.
He connected a high voltage battery to a discharge tube sealed at both ends and fitted with two metal plates called electrodes.
The metal plate connected to the positive terminal of the battery is called the anode.
The metal plate connected to the negative terminal of the battery is called the cathode.
A discharge tube consists of a tube through which gases can be removed using a vacuum pump.
The tube was filled with air, when he passed high voltage at normal pressure across the terminal of the tube filled with air, he found that no electricity could flow through the air.
On further reducing the pressure and applying high voltage, he observed that the glass walls of the tube glowed a bright-green colour.
He found that the greenish glow on the glass walls is due to the hitting of some invisible rays that traveled in straight lines which are emitted from the negative terminal(cathode).
He named these rays as cathode rays.
J J Thomson conducted experiments to understand the nature of cathode rays and found out that the cathode rays consists of negatively charged particles.
He named these negatively charged particles electrons.
