Use primary secondary step-up and step-down terms
Classify a transformer from its connected input winding and compare secondary turns and voltage with primary values.
Section P4.5.6 · The transformer
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
- Read turn counts.
- Distinguish input from output.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Does primary always mean the winding with more turns?
What you will learn
- Classify a transformer from its connected input winding and compare secondary turns and voltage with primary values.
- Assign transformer terms from connected roles and the output/input voltage comparison.
Roles depend on the connected arrangement
The primary receives input and the secondary provides output in the stated operating arrangement. A step-up transformer gives a greater secondary voltage than primary voltage; a step-down transformer gives a smaller secondary voltage. For the simple voltage-ratio model, more secondary turns than primary turns gives step-up action, and fewer gives step-down action.
Neither primary nor secondary means the larger coil by definition. A small-turn winding can be primary in a step-up arrangement, while a large-turn winding can be primary in a step-down arrangement. First identify which winding is actually connected to the source.
Keep classification within the stated model
With equal turns, the simple ratio gives equal voltages rather than step-up or step-down action. If the connected input/output roles are exchanged in a specified suitable arrangement, the classification can reverse. That statement does not authorise reversing real equipment connections or ignoring its ratings.
A greater voltage does not mean a greater created energy or universal current increase. Current and power behaviour depend on the load and are developed in the Supplement ideal-efficiency lessons. Use the stated simple ratio conditions and keep real specifications separate.
Sources for this lesson
Pause and explain
A 600-turn input and 150-turn output give which simple transformation?
Worked example
The source connects to a 200-turn winding and the output uses 800 turns. Classify the simple voltage transformation.
Show the worked solution
- The source-connected 200-turn winding is primary.
- The 800-turn output is secondary.
- More secondary turns give greater secondary voltage.
Answer Step-up in the specified simple model.
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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.
Classify the supplied 200-turn input and 800-turn output.
Give me a hint
Identify roles before comparing turns.
Compare my reasoning
- Primary has 200 turns.
- Secondary has 800 turns.
- Secondary turns are greater, giving step-up action.
Step-up.
Look for these in your work
- Label both roles.
- Compare output with input.
Classify 1000-turn input and 250-turn output.
Give me a hint
Use the output-to-input turn comparison.
Compare my reasoning
- The 1000-turn winding is primary.
- The 250-turn winding is secondary.
- The lower output turn count gives step-down action.
Step-down.
Look for these in your work
- Use connected roles.
- State the voltage comparison.
A specified suitable arrangement exchanges the input and output roles of those 1000- and 250-turn windings. Classify the new ratio without giving real wiring instructions.
Give me a hint
Keep the new input role explicit.
Compare my reasoning
- The new primary has 250 turns.
- The new secondary has 1000 turns.
- The simple model now gives step-up action.
Step-up for the newly specified roles; real ratings remain separate.
Look for these in your work
- Name the changed roles.
- Retain the model boundary.
Common mistakes
- Primary means input, not larger.
- Name the connected arrangement.
- Voltage increase is not energy creation.
What can you explain now?
Which voltage comparison describes step-down action?
Compare with the explanation
Secondary voltage smaller than primary
A step-down arrangement reduces output voltage relative to its input under the stated model.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Assign transformer terms from connected roles and the output/input voltage comparison.
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.