IB Physics B5

Current

The rate of flow of electrical charge, defined as I = ΔQ/Δt. SI unit is ampere (1A = 1C/s)

Voltage

The energy difference between two points in a circuit per charge, defined as V = W/q. SI unit is volt (1V = 1J/C)

Conventional current

A current that flows from the positive charge to the negative charge.

Electronic current

A current that flows opposite to the conventional current, from negative to positive.

Effects of electric current

Includes heating effect, magnetic effect, and chemical effect.

Electromotive force (emf)

The total energy difference per unit charge around a circuit. SI unit is volts.

Electric power supplied

Calculated as P = IV, where P is power, I is current, and V is voltage.

Ammeters

Devices that measure current, connected in series in a circuit.

Voltmeters

Devices that measure energy converted per unit charge, connected in parallel.

Electrical resistance

The ratio between potential difference and current, defined as R = V/I. SI unit is ohm (1Ω = 1V/A).

Ohm's law

States that current flowing through a piece of metal is proportional to the potential difference across it, providing temperature remains constant.

Ohmic behavior

When current and potential difference (pd) are proportional.

Non-ohmic behavior

When current and potential difference (pd) are not proportional.

Resistivity

A measure of the resisting power of a specified material to the flow of electric current.

Resistors in series

Total resistance R(total) is the sum of individual resistances: R(total) = R1 + R2 + R3 + …

Resistors in parallel

Total resistance is given by 1/R(total) = 1/R1 + 1/R2 + 1/R3 + …

Variable resistors

Resistors designed so that their resistance can be changed to a required value.

Thermistor

A resistor whose resistance depends on its temperature; typically has a negative temperature coefficient. ↑ T —> ↓ R

Light-dependent resistor (LDR)

A device whose resistance depends on the amount of light shining on it; increased light causes decreased resistance. ↑ light —> ↓ R

Current in series

is the same across the circuit

Current in parallel

is added up

Pd in series

is added up

Pd in parallel

is the same across the circuit