Electricity Flashcards
What is meant by an e.m.f of 12.8V?
12.8 J is gained by 1 coulomb of charge passing through a battery.
Suggest why wires in a circuit have a large diameter?
Wires with a large diameter have a low resistance.
What is irradiance?
The power per unit area.
How could you improve an irradiance experiment?
By using a more precise instrument to reduce the absolute uncertainty.
Insulator? (4)
Insulators have no free electrons to move on the outermost level.
Their valence band is full
The conduction band is empty
The band gap is large
Conductor? (4)
The Valence band is full
The outermost level has free electrons that move to conduct electricity
The conduction band contains some electrons
The band gap is small
Semiconductors? (4)
Most commonly used semiconductors are silicon and germanium. Both have a valency of four (four outer electrons available for bonding).
The resistance of semiconductors are very large are a few free electrons available to conduct.
What is a hole? (2)
When an electron leaves its position in the crystal lattice, there is a space left behind that is positively charged. The hole is thought of as a charge carrier.
Undoped semiconductor?
The number of holes in an u doped semiconductor is equal to the number of electrons.
Current in a semiconductor?
Current in a semiconductor consists of free electrons drifting in one direction and holes drifting in the other direction.
Doping n-type? (2)
If an impurity such as arsenic which has five outer electrons is present in the crystal lattice then the extra electron will conduct increasing the conductivity of the crystal and decreasing the resistance of the semiconductor. This type of semiconductor is called n-type because the movement of free electrons is negatively charged.
Doping p-type? (3)
Semiconductor doped by an element such as indium which has only three outer electrons. This produces a hole in the crystal lattice. Conduction then takes place by the movement of positive holes.
What charge do n-type and p-type semiconductors have?
N-type and P-type semiconductors have an overall neutral charge.
Photovoltaic mode? (5)
In this mode the diode has no bias voltage applied. The voltage is proportional to the light intensity.
Photons in the junction are absorbed which creates electron-hole pairs. A voltage is generated by the separation of electrons and holes. The higher the light intensity the more electron-hole pairs are produced.
LED? (4)
LED’s have forward biased p-n junction diodes. Holes and electrons will meet in the junction and combine to emit photons. If the junction is close to the surface material the light will escape. We call this process a Light emitting diode.
