Read cell and battery symbols with their polarities
Turn a source symbol into a labelled circuit description and distinguish a single cell from several cells.
Section P4.3.1 · Circuit diagrams and circuit components
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Identify a complete conducting path.
- Recall source e.m.f. and d.c. polarity.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is source e.m.f.?
What you will learn
- Draw cell and battery symbols.
- Interpret source polarity without confusing plate length with wire length.
Identify the source
A cell symbol has two parallel unequal lines. The longer line marks the positive terminal and the shorter line the negative terminal. The wires continue from opposite sides of the pair. Rotating the whole symbol does not change which plate is positive. This symbol represents electrical connections, not the physical shape of the cell.
A battery is represented by repeated long–short pairs: several cells form one source assembly. A drawing may show a representative number of pairs rather than every physical cell, so use any supplied label for the actual number and voltage. Do not assign a voltage solely from the length of a drawn plate.
Follow the connections
Trace the external path from one terminal through the components back to the other terminal. In a simple d.c. circuit with conducting loads, conventional current goes from positive to negative through that external path; electron movement in metallic parts is opposite. An open switch interrupts the path even though source e.m.f. can remain.
When drawing, use clear straight connecting lines and recognizable component symbols. Label the source and show polarity where interpretation depends on it. A sketch of a battery case does not replace a circuit symbol. Source combinations and their signed e.m.f. are taught in the series-circuit pathway.
Sources for this lesson
Pause and explain
A cell symbol is rotated through a right angle. Which plate is positive?
Worked example
Describe a source drawn with one long plate on the left and one short plate on the right.
Show the worked solution
- One unequal pair represents a cell.
- The long plate is positive; the short plate is negative.
- In a completed external d.c. path, conventional current leaves the left positive terminal.
Answer One cell, positive left and negative right.
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Draw a cell with positive left, negative right, and wires from both terminals.
Give me a hint
Use one unequal pair and identify polarity independently of orientation.
Compare my reasoning
- Draw two parallel plates across the wire direction.
- Make the left plate longer and label it +.
- Make the right plate shorter and label it −; extend connecting wires outward.
One long + plate on the left and one short − plate on the right, with terminal wires.
Look for these in your work
- Use a recognized symbol.
- Label both polarities.
Draw a battery symbol representing several cells, then explain how it differs from a cell symbol.
Give me a hint
Compare repeated unequal pairs with one pair.
Compare my reasoning
- Repeat the long–short plate pairs along the source line.
- Connect the outer ends to the circuit.
- State that one pair denotes a cell and repeated pairs denote a battery.
Repeated long–short pairs represent a battery; one pair represents a cell.
Look for these in your work
- Keep plate lengths distinct.
- Do not invent an unlabelled voltage.
A learner infers 12 V from a battery symbol with long plates and says an open switch makes its e.m.f. zero. Assess both claims.
Give me a hint
Separate a drawing convention, a supplied rating and a complete path.
Compare my reasoning
- Plate lengths distinguish polarity, not voltage.
- A source rating must be supplied or measured.
- An open switch prevents complete-path current but need not remove source e.m.f.
Neither claim follows: a voltage rating needs evidence, and opening the path need not remove e.m.f.
Look for these in your work
- Correct both inferences.
- Distinguish source voltage and circuit current.
Common mistakes
- Plate length marks polarity, not voltage.
- A rotated cell keeps the same polarity labels.
- An open circuit can retain a source voltage.
What can you explain now?
What does the longer cell-symbol plate identify?
Compare with the explanation
Positive terminal.
Its length is a polarity convention, not a measure of the source voltage.
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Make it stick
Draw cell and battery symbols and identify the positive terminal from the longer plate.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.