Edexcel GCSE Physics (1PH0) — Electricity and circuits
Every time you plug a charger into a wall socket, you are connecting to a power source where the electricity is constantly vibrating rather than flowing in a single, continuous loop. This type of electrical supply is known as alternating current (a.c.).
This direction reversal happens because the power source has an alternating polarity. The terminals constantly switch between positive and negative. Since current always flows from the positive terminal to the negative terminal at any given moment, the changing polarity forces the electrons to continuously reverse their direction.
Energy is transferred by the oscillation of these electrons. Even though the electrons themselves do not move through the whole circuit, they transfer energy to the components (like a lightbulb or heater) as they "slosh" back and forth, colliding with the ions in the conductor.
The UK domestic mains supply operates using an alternating current with two specific parameters that you must recall:
The frequency of an alternating current is the number of complete back-and-forth cycles it makes each second. A frequency of means the current completes 50 full cycles every second. Because the current reverses direction twice per cycle, it actually changes direction 100 times every second.
When asked to 'describe' alternating current, Edexcel examiners look specifically for the phrases 'constantly changes direction' or 'moves back and forth' — use these exact words to secure your marks.
Students often think electrons travel all the way from the power station to the appliance in an a.c. circuit, but actually, they just vibrate back and forth locally to transfer energy.
You must memorise the values for the UK mains supply ( and ) as they are frequently tested in 'recall' questions.
Alternating current (a.c.)
A current that continuously and periodically changes its direction, with charge carriers moving back and forth.
Charge movement
The physical oscillation of charge carriers (usually electrons) through a conducting material.
Potential difference
The energy transferred per unit charge between two points in a circuit, measured in volts (V).
Frequency
The number of complete cycles an alternating current makes every second, measured in Hertz (Hz).
Put your knowledge into practice — try past paper questions for Physics
Alternating current (a.c.)
A current that continuously and periodically changes its direction, with charge carriers moving back and forth.
Charge movement
The physical oscillation of charge carriers (usually electrons) through a conducting material.
Potential difference
The energy transferred per unit charge between two points in a circuit, measured in volts (V).
Frequency
The number of complete cycles an alternating current makes every second, measured in Hertz (Hz).
