electricity

AC current

changes direction and instantaneous value with time

EMF

the energy supplied to each coulomb of charge passing through the battery.

Lost volts

The potential difference across the internal resistor of a source of e.m.f.

Internal resistance

resistance inside the source of electrical energy.

terminal potential difference (t.p.d.)

Voltage that appears across the terminals of a source when the source is supplying a current to a circuit. It is the potential difference that appears in the circuit.

short circuit

A connection that allows current to take the path of least resistance

open circuit

an incomplete electrical circuit in which no current flows

Information from a Vtpd vs Current Graph.

Y Intercept - EMF

X Intercept - Short Circuit Current

Gradient = -r

1 Farad

1 coulomb of charge stored per unit volt

Capacitance (C)

Measured in Farads (F)

Charge (Q)

Measured in Coulombs (C)

Area under a Q vs V graph.

Energy Stored in a capacitor.

Voltage vs Time for Charging Capacitor

Current vs Time for Charging Capacitor

Voltage vs Time for Discharging Capacitor

Current vs Time for discharging Capacitor

Adding a resistor in series to an internal resistance circuit.

Resistance increases.

Current decreases.

Lost volts decrease.

VTPD increases

Removing a resistor from a internal resistance circuit. Or adding in parallel.

Resistance decreases

Current increases

Lost volts increase

VTPD decreases

Capacitor/Resistance Circuit - What happens when you increase resistance?

Initial Current reduces.

Longer time to charge.

Capacitor/Resistance Circuit - What happens when you increase capacitance?

Longer time to charge.

Same final voltage.

conduction band

A band higher in energy than the fully occupied valence band. Will have electrons free to move in this energy band.

valence band

The highest energy band that is fully occupied.

For conduction to occur you need

Free electrons, accessible empty states

Conductivity increases with temperature increasing

Semiconductor

Conductivity decreases with temperature increasing.

Conductor

Has partially filled valence and conduction bands.

Metals (Conductors).

Has a filled valence band.

Insulators.

At room temperature there is enough energy to move electrons from valence to conduction band.

Semiconductor.

Term to describe adding impurities to semiconductor.

Doping

Why are semiconductors doped?

To increase conductivity.

Negative terminal connected to N-Type

Positive terminal connected to P-Type

Forward bias

Positive terminal connected to N-Type

Negative terminal connected to P-Type

Reverse bias

Forward bias does what to the depletion layer?

Makes it smaller, reduces electric field

Reverse bias does what to the depletion layer?

Makes it larger, increases electric field

For an LED to light it needs to be in ...

Forward Bias

For a solar cell to produce electricity it needs to be ...

Unbias

When the LED is forward bias it works because ....

Voltage applied causes electron from the conduction band of the n type to move towards the conduction band of p type. Electrons fall from the conduction band to valence band, photon emitted.

A solar cell works because...

Electrons gain/absorb energy from photons/light, electrons move form valence band to conduction band. Electrons move towards n-type semiconductor (producing a P.D.)