Deck 'C' Flashcards
What is an energy band?
Where electron orbitals are influenced by other close atoms, thus there are no longer discrete energy levels.
What is the valence band?
The band of electrons containing the outermost electrons of the atom.
What is the conduction band?
The band of electrons with energy levels further from the nucleus than the forbidden band. These electrons are free of their original atom.
Describe energy bands in a conductor.
- Conduction and valence bands overlap
- Many electrons are in the conduction band
- Electron collisions increase with temperature, increasing resistance
Describe energy bands in a semiconductor.
- Small gap between the C-band and V-band (the forbidden gap)
- More energy is required to bridge the gap
- Increased temperature means increased energy, so resistance decreases
Describe energy bands in an insulator.
- Significant forbidden gap
- No electrons in the conduction band
- Increasing temperature means a smaller gap and increased energy, so electrons are more likely to jump the gap
What is electricity?
The flow of electrons in a material.
What is electrical current?
A measure of the rate of flow of electrons (from an area of negative charge to an area of positive charge).
What is potential difference?
The driving force causing electron flow; work done moving 1 Coulomb of charge.
What is electromotive force (EMF)?
The potential energy developed across a source of electricity.
What are the sources of electric potential difference?
- Friction
- Magnetism
- Chemicals
- Light
- Heat
- Pressure
What is electrical resistance?
Where electrons collide with atoms of the conducto as they move along, thus impeding the current.
How does resistance vary in materials?
- R is proportional to length (more to collide with)
- R is proportional to 1/cross-sectional area (more electrons available)
- R = V/I
How does resistance change in series and parallel?
- Series –> R = R1 + R2 + R3
* Parallel –> 1/R = 1/R1 + 1/R2 + 1/R3
