Modern physics

Thermionic emission

The release of electrons from the surface of a hot metal

Cathode Ray Tube

Kinetic energy formula

1/2 mv²

Kinetic energy =

qV

q= charge on one electron

V= high voltage

X-rays

Are produced when high-energy electrons collide with a high density target. They are a high frequency form of electromagnetic radiation.

Who discovered x-rays?

Wilheim Rontgen

The photoelectric effect

The emission of electrons from the surface of a metal when light of a suitable frequency shines on it.

How to demo P.E.

1: negatively charge a G.L.E.

2: Shine U.V. Light on G.L.E.

3: leaves collapse → electrons emitted

The photocell

Einstein’s explanation of the photoelectric effect

Diagram of an X-Ray tube

	1. The low voltage supplies power to a filament.
	2. Electrons are emitted from the filament due to thermionic emission.
	3. They get accelerated across the vacuum due to the very high voltage and smash into the high-density anode (usually tungsten).
	4. Most of the kinetic energy gets converted to heat, which must be removed with a coolant.
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	6. These X-rays are emitted in all directions.
	7. Most of these get absorbed by the lead shielding, but some exit through a narrow window, where they are then used for the required purpose.