Read simple circuit situations using charge flow, energy per charge and conductor properties.
Method and worked examples
Current is charge flow per second, measured in amperes. Voltage is energy transferred per unit charge, measured in volts. A closed conducting path allows current. Metals contain mobile electrons; insulators strongly restrict their movement. Lamps transfer electrical energy while charge continues around the circuit rather than being consumed.
In one series loop, current is the same throughout and voltage is shared between components. Parallel branches connected to the same two points have equal voltage and provide separate current paths. Opening a series connection stops its loop; opening one parallel branch need not stop another. Calculate current = charge / time and voltage = energy / charge.
Example 1
12C of charge passes a point in 4s. Calculate the current.
Current = charge / time =412=3A.
Example 2
A battery transfers 18J to 3C of charge. Find the voltage.
Voltage = energy / charge =318=6V. This describes energy per charge, not the rate of charge flow.
Watch out:A lamp transfers electrical energy. In a steady single series loop, the current is the same before and after it.
Current, voltage and circuit pathways | Year 9 Science | Ascent Arcade