The Electron Flashcards
Thermionic Emission
The giving off of electrons from the surface of a hot metal
Uses of Cathode ray tube
- Cathode ray Oscilloscope
- Old TVs
- The ECG
Properties of cathode rays
- Travel in straight lines
- Cause certain substances to fluoresce
- Can be deflected in electric and magnetic fields
- Can produce x-rays when they strike heavy metals
The Electronvolt
Is the energy lost or gained by an electron when it accelerates through a potential difference of one volt.
The Photoelectric effect
The emission of electrons from a metal due to electromagnetic radiation of a suitable frequency falling upon it
A photon
Is a bundle of electromagnetic radiation
Potential energy equation
W=QV
1 eV = xJoules
1.6x10-19
The Photocell- Operation
- Light shines on photo-cathode.
- Electrons are released (photoelectric effect)
- The electrons are attracted to the anode and from there they flow around the circuit, where they can be detected by the galvanometer.
Uses of Photocells
Burglar alarms, automatic doors
X-rays are produced..
When high-energy electrons collide with a high density target
X-rays- Operation
- The low voltage supplies power to a filament which in turn heats the cathode
- Electrons are emitted from the hot cathode
- They get accelerated across the vacuum and smash into the high density anode.(tungsten)
- Most of the kinetic energy turns to heat which must be removed with coolant.
- Some inner electrons in the tungsten get bumped up to a high orbital, then quickly fall back down to a lower level, emitting x-rays in the process.
- Most of these x-rays get absorbed by the lead shelling. There is a gap in the shelling for the controlled emission of x-rays.
Properties of X-rays
Electromagnetic waves, Cause ionisation of atoms, High penetrating powers.
Uses of X-rays
Medicine: to detect broken bones
Industry: To detect breaks in pipes
