WJEC GCSE Physics 1.1 Electric Circuits Exam Questions

About WJEC GCSE Physics 1.1 Electric Circuits

Electric circuits is the first topic of WJEC GCSE Physics Unit 1 and supplies the equations used throughout the electricity work. You need to draw and interpret circuit symbols, apply the rules for current and voltage in series and parallel circuits, and use ammeters and voltmeters correctly. You must use V = IR, combine resistances in series and parallel, and use E = Pt, P = VI and P = I^2R. The behaviour of resistors, filament lamps, diodes, LDRs and thermistors is covered, and the I-V characteristic investigation is a specified practical. Examiners often combine a circuit diagram with a multi-step calculation, so practise rearranging equations.

What you need to know

• Circuit rules In series, the current is the same everywhere and the supply voltage is shared between components. In parallel, the voltage across each branch equals the supply voltage and the current splits between branches.
• Meters Ammeters are connected in series and measure current in amperes (A). Voltmeters are connected in parallel across a component and measure voltage in volts (V).
• Resistance V = IR. In series, R = R1 + R2. In parallel, 1/R = 1/R1 + 1/R2, so the total is less than the smallest resistor. Adding resistors in series increases total resistance; adding them in parallel decreases it.
• I-V characteristics A fixed resistor gives a straight line through the origin (constant resistance). A filament lamp curves because its resistance increases as it gets hotter. A diode only lets current flow one way. Investigating I-V characteristics is a specified practical.
• Sensors An LDR's resistance falls as light intensity increases. An NTC thermistor's resistance falls as temperature increases. They are used in potential divider style circuits to control lamps and heaters.
• Power Power is energy transferred per second: E = Pt, P = VI and P = I^2R. Power is in watts (W), energy in joules (J).

Common mistakes in 1.1 Electric Circuits

• Connecting a voltmeter in series. A voltmeter must be connected in parallel across the component being measured.
• Adding parallel resistors as if they were in series. For parallel resistors use 1/R = 1/R1 + 1/R2, and remember to take the reciprocal at the end.
• Saying current is used up as it passes through components. Current is the same before and after a component in series; it is energy that is transferred.
• Describing a filament lamp's resistance as decreasing with current. It increases because the filament gets hotter.

Try three 1.1 Electric Circuits exam-style questions