Question 1

What is the difference between series and parallel circuits?

Accepted Answer

In a series circuit, components are connected end-to-end in a single loop, so the same current flows through each component. The total resistance is the sum of individual resistances, and the voltage is shared across the components. In a parallel circuit, components are connected across the same two points, creating multiple paths for current. The voltage across each branch is the same, but the current splits, and the total resistance is less than the smallest individual resistance.

Question 2

How do I calculate total resistance in a parallel circuit?

Accepted Answer

For two resistors in parallel, use the formula 1/R_total = 1/R1 + 1/R2. For example, if R1 = 4 Ω and R2 = 6 Ω, then 1/R_total = 1/4 + 1/6 = 3/12 + 2/12 = 5/12, so R_total = 12/5 = 2.4 Ω. For more than two resistors, keep adding reciprocals. Remember that the total resistance is always less than the smallest resistor in the parallel network.

Question 3

Why does a filament lamp have a curved I-V graph?

Accepted Answer

A filament lamp is a non-ohmic conductor because its resistance increases as it gets hotter. When current flows, the filament heats up, causing the metal ions to vibrate more, which impedes electron flow. This means that as voltage increases, the current increases but at a decreasing rate, producing a curved I-V graph. The graph is not a straight line through the origin, unlike an ohmic conductor at constant temperature.

Question 4

What is the difference between AC and DC?

Accepted Answer

DC (direct current) flows in one direction only, like from a battery. AC (alternating current) changes direction periodically, like the mains supply in the UK (50 Hz). In AC, the voltage also alternates sinusoidally. Most electronic devices use DC internally, so they have a rectifier to convert AC to DC. In circuits, DC is easier to analyse, but AC is more efficient for long-distance power transmission.

Question 5

How do I use an ammeter and voltmeter correctly in a circuit?

Accepted Answer

An ammeter measures current and must be connected in series with the component you are testing, so that all the current flows through it. A voltmeter measures potential difference and must be connected in parallel across the component, so it measures the voltage drop. Ammeters have very low resistance to avoid affecting the circuit, while voltmeters have very high resistance to minimise current through them.

Question 6

What is electrical power and how do I calculate it?

Accepted Answer

Electrical power is the rate at which electrical energy is transferred to other forms (e.g., light, heat). It is measured in watts (W). The main formula is P = IV, where P is power, I is current, and V is voltage. You can also use P = I²R (if you know current and resistance) or P = V²/R (if you know voltage and resistance). For example, a 12 V bulb with a current of 0.5 A has a power of 12 × 0.5 = 6 W.

Topic 10 – Electricity and circuits

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Related Topics in EDEXCEL GCSE Physics

Topic 1 – Key concepts of physics

Topic 11 – Static electricity

Topic 12 – Magnetism and the motor effect

Topic 13 – Electromagnetic induction

How to Revise Topic 10 – Electricity and circuits — Edexcel GCSE Physics

Examiner Tips for Topic 10 – Electricity and circuits

Common Mistakes in Topic 10 – Electricity and circuits

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