- Current is the number of coulombs per second (amps)
- The strength of an electric current is measured in amps
- Amps are a measure of how much electric charge is flowing round the circuit
- Current flowing in a circuit can be measured using an ammeter
- Ammeters must be connected in series with the components
Current (A) = Charge (C) / Time (s)
- Electric current flows when electrons flow and collide with atoms in a conductor
- These collisions make the conductor hot
- This is called resistance and it makes it harder for current to flow
- Resistance is measured in ohms
Resistance (ohms) = Voltage (volts) / Current (amps)
- p.d is measured in volts
- When two or more cells are connected in series, the total p.d is the sum of both cells
- p.d across a component in a circuit is measured using a voltmeter
- The voltmeter must be connected in parallel with the components
- The p.d across a device equals the amount of energy changed (in joules) per coulomb of charge passing through it
e.g. the voltage across a lamp is 3V. What does this mean?
- That 3J per coulomb are passing through the lamp and are converted into electrical energy.
Potential Difference (V) = energy transferred (J) / charge passes (C)
Current : Voltage graphs:
The current flowing through a resistor at a constant temperature is directly proportional to the voltage across the resistor.
So, if you double the voltage, the current doubles too.