Circuit diagrams, series and parallel circuits
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 2 worked examples, 4 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Why do house lights stay on?
- Circuit symbols
- A series circuit
- Series resistance
Read the transcript of the teaching part
Last time
Before we start: last time, in Resistance, Ohm’s law and I–V graphs, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Why do house lights stay on?
Old Christmas lights were wired so that when one bulb failed, the whole string went dark. In your house, one lamp can fail and the rest stay on. The difference is series and parallel wiring, and each behaves differently for current, voltage and resistance.
Circuit symbols
A cell, a battery of cells, a switch, a lamp, a fixed resistor and a variable resistor all have their own symbol. An ammeter has an A in a circle and goes in series. A voltmeter has a V in a circle and goes in parallel. Others to know: fuse, diode, thermistor, LDR, and a heater.
A series circuit
In a series circuit, the components are connected one after another, in a single loop. The current is the same at every point. The p.d. of the supply is shared between the components, so the voltages add up to the supply voltage.
Series resistance
The total resistance of resistors in series is the sum of their resistances. It is always bigger than any single resistor. Adding more lamps in series makes the current smaller, and every lamp dimmer.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Circuit diagrams and components · Combined resistance · Series and parallel circuits · Circuit diagrams and components · Combined resistance · Current and voltage in series and parallel circuits.
The whole chapter: Electric Circuits, Electric Circuits.
Chapter 4.3: Electric circuits
- Circuit diagrams, series and parallel circuits 6 min
- Potential dividers, thermistors and LDRs 5 min
Also for O Level Physics 5054
Which topics come up most in O Level Physics 5054 past papers, counted from every paper since 2004.