Recall and use the circuit symbols shown in Section 6 of the Cambridge A‑Level Physics (9702) syllabus.
Key Circuit Symbols
Symbol
Name / Function
Typical Use in Experiments
⎓⎓
Battery (ideal emf source)
Provides a constant potential difference.
⎓⎓ (with internal resistance symbol)
Battery with internal resistance
Real cell where $r$ is shown inside the symbol.
—|—
Resistor
Controls current; value $R$ indicated.
—|— (with wavy line)
Variable resistor / rheostat
Adjustable resistance in a circuit.
—|— (with arrow)
Diode (forward direction shown by arrow)
Allows current in one direction only.
—|— (with two arrows)
LED (light‑emitting diode)
Used as a visual indicator.
—|— (with a circle)
Capacitor
Stores charge; value $C$ indicated.
—|— (with a coil)
Inductor
Produces magnetic field; inductance $L$ indicated.
—|— (with a line and a dot)
Switch (open/closed)
Controls the flow of current.
—|— (with a “V”)
Voltmeter (connected in parallel)
Measures potential difference.
—|— (with an “A”)
Ammeter (connected in series)
Measures current.
—|— (with a “Ω”)
Ohmmeter (used to measure resistance)
Connected across the component being measured.
Suggested diagram: A simple series circuit showing a battery, a resistor, a switch, an ammeter and a voltmeter.
Using the Symbols in a Circuit Diagram
When drawing a practical circuit for an experiment, follow these conventions:
Place the battery symbol on the left-hand side, with the positive terminal at the top.
Connect the ammeter in series with the load (e.g., a resistor) so that the same current passes through it.
Connect the voltmeter in parallel across the component whose voltage you wish to measure.
Use a switch symbol to indicate where the circuit can be opened or closed safely.
Label each component with its nominal value, e.g., $R = 10\;\Omega$, $C = 100\;\mu\text{F}$.
Example: Determining Internal Resistance of a Cell
Consider the circuit shown in the figure below (use the suggested diagram as a guide). The symbols used are:
Battery with internal resistance $r$.
External resistor $R$.
Ammeter $A$ (in series).
Voltmeter $V$ (across the battery terminals).
The relationships are:
$$ I = \frac{E}{R + r} $$
$$ V = E - Ir $$
By measuring $I$ and $V$ for several values of $R$, you can plot $V$ against $I$ and obtain $r$ from the gradient.
Suggested diagram: Circuit for measuring internal resistance – battery with $r$, external resistor $R$, ammeter $A$, voltmeter $V$.
Practice Questions
Identify the symbols needed to draw a circuit that measures the resistance of an unknown resistor using a Wheatstone bridge. List each component and its symbol.
In a circuit containing a battery ($E = 12\;\text{V}$, $r = 0.5\;\Omega$), a resistor $R = 4\;\Omega$, an ammeter and a voltmeter, calculate the current shown by the ammeter and the voltage read by the voltmeter. Show your working using the symbols from the table.
Explain why a voltmeter must be connected in parallel and an ammeter in series, referring to the symbols and their function.
Draw (in words) a circuit diagram for a simple LED circuit powered by a 9 V battery, including a current‑limiting resistor. Indicate the direction of current flow with arrows on the symbols.
Summary
Mastering the circuit symbols in Section 6 enables you to:
Accurately record experimental setups.
Interpret and analyse circuit diagrams in exam questions.
Communicate findings clearly using standard notation.