A switch is not connected to a bulb merely because it is drawn next to it. Nor does one open switch necessarily make every bulb in a circuit go out. The answer depends on which complete paths the switch interrupts. A useful PSLE Science explanation should predict the stated results for the actual connections, not rely on the visual position of a symbol or a remembered slogan.
This workshop teaches one particular performance job: use switch-state evidence to test a circuit-path explanation. You will read which switches are open or closed, predict which bulbs have a complete path and compare that prediction with a proposed answer or results record. When two explanations fit one observation, you will identify another stated switch condition that can distinguish them.
Every circuit and result below is an original paper example, not a report of a physical experiment. No construction is required. Use pencil sketches when helpful, and do not connect household mains electricity, open electrical appliances or join battery terminals directly. The examples assume working components and suitable cells and bulbs. Every complete bulb path described is assumed to light the bulbs on it; we are checking on-or-off behaviour, not calculating brightness.
Keep the topic foundation and the evidence test separate
The existing guide to which switch controls which bulb and circuit-path and fault-diagnosis guide develop the underlying electrical-system ideas. Return to those routes if you cannot yet trace a complete circuit. This workshop adds a checking task: does a proposed explanation account for every relevant switch state and bulb result?
A complete path in the simple models here connects the two terminals of the cell through the working bulb or bulbs. An open switch creates a break in its path. A closed switch joins its contacts. A circuit with separate branches can retain a complete path through one bulb while another branch is broken. These principles, rather than physical closeness on the page, drive the predictions.
For the underlying distinction, OpenStax’s account of series circuits describes components sharing one current path, while its parallel-circuit chapter describes separate paths. Those references go beyond Primary 6 in places; you do not need their calculations for the on-or-off reasoning here. The worked tests below are original deductions from the explicitly stated connections.
A switch state is an input, not a conclusion
Read open and closed carefully. In this context, closed means the switch contacts meet and can complete their part of the path. Open means the contacts are separated. Everyday language about opening a tap can tempt a learner to reverse these meanings. Use the circuit description rather than an unrelated everyday analogy.
A result statement such as P lights is an output. A condition such as S1 is closed is an input. An explanation connects them through the wiring. Do not jump from one input to an output without checking the other switches and any shared part of the circuit.
For example, closing a branch switch cannot light its bulb if a shared main switch still breaks the connection to the cell. The branch switch may be necessary, but it is not sufficient under that state. A complete answer names the other required connection instead of assuming every closed switch guarantees a lit bulb nearby.
Trace one bulb at a time
Begin with the bulb named in the question. Find a continuous route through it that connects the cell’s terminals, respecting the stated switch positions. If that route contains an open switch or an explicit gap, it is broken. If another route through the same bulb is supplied, examine that too. Do not jump from one unconnected line to another to complete a path mentally.
When two bulbs are present, repeat the check for the second bulb. This avoids treating the circuit as a single yes-or-no object when its branches can behave differently. You may conclude P off and Q on. That is not an inconsistency; it can be exactly what the connections require.
Use the diagram’s junction marks and key when a real question provides them. In the text-only cases here, each junction and connection is stated in words. A sketch is only a memory aid. Moving a line or symbol to make your sketch tidy must not change what it connects to.
Worked test 1: one switch anywhere in a single loop
The paper circuit has one cell, one bulb P and one switch S in a single loop, with no branches. The loop goes from one cell terminal through P, then S, and back to the other terminal. A learner claims that opening S will not affect P because the switch is after the bulb in the drawn route.
With S closed, the loop is complete and P lights under the stated assumptions. With S open, the loop is broken and P does not light. The bulb does not remain lit merely because it appears before the gap when you trace from one chosen terminal. The whole path must be complete.
The decisive test is the state with S open. The learner’s claim predicts P on, while the single-loop model predicts P off. Explain the failure by naming the broken loop, not by saying only that the switch is wrong. The location of the gap within this one loop does not make it irrelevant.
Now redraw the loop so S appears before P on the page, without changing the connections. The predicted on-or-off results remain the same. This redraw tests whether you follow connections or picture position. A different drawing can represent the same circuit.
Worked test 2: two bulbs do not automatically mean two paths
A cell, switch S, bulb P and bulb Q form one continuous loop with no branches. The bulbs are working, and the cell is suitable for the stated model. Predict their states when S is closed and when it is open.
With S closed, both bulbs have the shared complete loop and light. With S open, the loop is broken and both are off. There is no separate return path for P or Q. Counting two bulb symbols does not create two independently complete circuits.
A wrong explanation says that the bulb nearer the cell lights even when the switch is open. It assumes that current can use only the first portion of the loop and ignore the missing return. The repair is to trace the entire route through both bulbs and S to the other cell terminal.
A second wrong explanation says electricity is used up by P before it reaches Q. That is not the account used for a steady series circuit. The OpenStax treatment of series and parallel connections distinguishes current through the series path from energy transferred in components. For this task, stay with the observable prediction: the stated complete loop lights both working bulbs; opening it interrupts both.
Worked test 3: two branch switches can act independently
Imagine two junctions, J and K. J is connected to one terminal of a cell and K to the other. Branch one runs from J through S1 and bulb P to K. Branch two runs from J through S2 and bulb Q to K. There are no other switches or gaps.
If S1 is closed and S2 open, P has a complete route and Q does not. If S1 is open and S2 closed, Q lights and P does not. If both switches are closed, both bulbs light. If both are open, neither lights. Those four states cover all combinations of the two switches.
A learner claims that any open switch makes both bulbs go out. The state S1 closed and S2 open disproves that claim for this arrangement: the P branch still connects J to K through P. The open S2 lies on Q’s branch, not on every path through the circuit.
Do not generalise the result to every pair of bulbs. It depends on the stated separate branches. If the bulbs were in the single loop of Test 2, one break would affect both. The purpose of comparison is to identify which connection changed, not memorise a result attached to the letters P and Q.
Worked test 4: add a main switch shared by both branches
Keep the two branches from Test 3, but insert switch M between the cell’s first terminal and junction J. Every route from that terminal to either bulb now passes through M. The return from K to the other terminal remains intact.
When M is open, neither bulb lights, whatever positions S1 and S2 have. Their branch contacts may be closed, but the shared supply route is broken. When M is closed, the branch switches again determine which of P and Q has a complete path.
Write one complete condition for each bulb: P requires M and S1 closed; Q requires M and S2 closed. These conditions are more precise than saying M controls everything or S1 controls P, because they show how the switches act together in the present circuit.
Test a proposed result: M open, S1 closed, S2 closed, both bulbs on. That record conflicts with the stated working circuit. Closing both branches does not repair the open shared connection. Check the main switch before explaining differences between the branches.
Worked test 5: choose between two candidate explanations
A question offers two possible descriptions of switch S. In Candidate A, S lies on a shared connection used by both bulbs. In Candidate B, S lies only on P’s branch, while Q has an intact separate path. All components work. With S closed, both bulbs light. With S open, P goes out but Q remains lit. Which candidate fits?
Both candidates explain the closed-switch observation. That observation alone does not distinguish them. The open-switch observation does: Candidate A predicts both off, while Candidate B predicts P off and Q on. Candidate B fits both records under the stated assumptions.
Your explanation should name the decisive record. Saying B is correct because both bulbs light with S closed gives evidence that also fits A. The stronger answer is that Q remains lit when S opens, so S cannot be on the only shared connection required by both bulbs in the proposed designs.
This selects between the supplied candidates; it does not reconstruct every possible hidden circuit in the world. Different detailed arrangements can sometimes produce the same limited observations. Keep the conclusion inside the alternatives and assumptions the task provides.
Worked test 6: a main-switch state can hide the branch distinction
Use the circuit with main switch M and branch switches S1 and S2. An observation says both bulbs are off while M is open. A learner concludes that both branch switches must also be open. Is that conclusion justified?
No. M being open already prevents both bulbs from having complete paths. S1 and S2 could be open or closed without changing that observed result. The state of the main switch hides what the branch switches would do if the shared connection were completed.
To distinguish the branch states in a paper prediction, consider M closed while keeping the branch conditions specified. You can then ask which bulb lights. In a real assessment question, do not invent a measurement that was never supplied; state what another informative test would need to change if the task asks you to suggest one.
The important distinction is between a result compatible with a claim and a result that establishes it. Both off is compatible with both branch switches open, but it is also compatible with several other states while M is open. One observation may not provide enough information for the proposed inference.
Worked test 7: two switches in the same single path
A cell and bulb P form a single loop containing switches S1 and S2 one after the other. There is no alternative route around either switch. Predict whether closing just one switch is enough to light P.
It is not. Both must be closed. The four switch states give these results: both open, P off; S1 closed with S2 open, P off; S1 open with S2 closed, P off; both closed, P on. Each single-open state leaves a gap in the only route through P.
A learner who says either switch can light the bulb may be imagining two alternative paths rather than the one path described. Ask the learner to point to the supposed route that avoids the remaining open switch. If no such connection exists, the explanation has added a wire that the question did not supply.
This is a useful place to use ordinary language precisely. Both means the two requirements must be satisfied together. Either one is enough means there are alternative ways to complete the relevant connection. The physical layout decides which statement is true.
Worked test 8: alternative switch paths join before one bulb
A cell terminal connects to junction J. Two short routes run from J to K: one contains S1 and the other contains S2. After they rejoin at K, the route passes through bulb P and returns to the other cell terminal. Every completed route includes P; the switch branches are not connected directly across the cell without a bulb.
If S1 alone is closed, it completes the J-to-K connection and P lights. If S2 alone is closed, P also lights. If both are closed, P still has a complete path. If both are open, neither J-to-K route is available and P is off.
The contrast with Test 7 is the connection between the switches, not their names. In Test 7, the single path requires both. Here, either alternative route can complete the missing section before P. Trace those routes explicitly rather than applying a universal two-switch rule.
Do not add a claim that closing both makes P exactly twice as bright. These examples establish path availability and on-or-off behaviour, not numerical brightness. The additional statement would require other electrical information and a different task. Answer what the model and evidence actually support.
Worked test 9: a nearby symbol does not own the bulb
A drawing places S1 beside Q for convenience, but its connecting wires put it on P’s branch. S2 lies on Q’s branch. The junctions are clearly marked, and the two branches connect the cell terminals independently. S1 is opened while S2 remains closed. Which bulb goes out?
P goes out because its branch is interrupted by S1. Q remains on through its branch and closed S2. The spatial closeness of the S1 label to Q on the drawing does not change the actual connections. Follow the wire, not the shortest distance between symbols.
A suitable repair to a wrong explanation is to redraw each branch separately while keeping the same junctions. Place S1 visibly beside P in your rough sketch to expose the relationship. The redraw is valid only if every connection remains the same; it is not permission to move the switch to another branch.
When no diagram is provided, as in this text practice, rely on the stated connections. When a diagram is provided, use its junction conventions. A crossing without an indicated connection must not be treated as a junction merely to make a preferred answer work.
Worked test 10: a closed switch cannot repair another gap
The cell supplies two separate branches. P’s branch contains a closed switch and a working bulb, but the final wire back to the return junction is explicitly disconnected. Q’s branch is complete and its switch is closed. Predict the result.
P is off because its path still contains a gap. Q is on because its complete branch does not use that disconnected wire. The statement P’s switch is closed is true, but it does not establish that every other part of P’s circuit is connected.
A learner’s answer might say, “P lights because its switch is closed.” Add the missing audit: trace from one cell terminal through P and all the way back to the other terminal. The trace stops at the disconnected return. That is the decisive evidence against the proposed answer.
If the task states that the wire is reconnected, the prediction changes. P then has a complete route, assuming the other stated conditions remain. Track which gap was repaired instead of treating any mention of a connection as a reason to change every bulb result.
Worked test 11: removal from one branch need not break another
P and Q occupy separate branches between the same supply and return junctions. Both branches are initially complete. The question then states that P is removed, leaving an open gap in its own branch. No other wire or component is changed. What happens to Q?
Q can remain lit because its route through the cell is still complete. The open gap where P was located belongs only to P’s branch. The question does not state that the whole supply has been disconnected. Do not import the result from a single series loop into this different arrangement.
Now place P and Q in one series loop instead and remove P, leaving the gap. Q goes out because the one available loop is broken. The same action, removing P, has a different consequence because the connections differ. Identify the circuit structure before describing the effect.
The deeper topic route is the existing guide to removing a bulb. This contrast is included here to test an explanation against a changed path, not to replace that complete topic lesson.
Worked test 12: distinguish a hypothetical prediction from a recorded result
A practice question describes the independent branches of Test 3 and asks what should happen with S1 open and S2 closed. The prediction is P off and Q on. That is a deduction from the supplied idealised circuit, not a measurement you personally performed.
A different question supplies an actual record saying both bulbs were off in that state and asks you to evaluate it. First confirm that you read the switch labels and results correctly. Under the stated all-working independent-branch model, the Q-off observation would not match the prediction. A fault, an omitted connection detail or an inaccurate record could be relevant possibilities if the question permits them.
Do not silently alter the record to P off and Q on and claim the observation agrees. Equally, do not abandon the complete-path principle merely because one record conflicts with the stated setup. Identify the mismatch and say which assumption or record would need checking.
The command decides the response. Predict asks what follows from the model. Describe reports the supplied observation. Evaluate compares the two and considers whether the evidence supports a conclusion. Mixing those jobs can make a scientifically informed answer respond to the wrong question.
Worked test 13: separate independent trials from a sequence
An independent-trial table specifies the full switch state in each row. Read each row fresh. If row one says S1 closed and S2 open, and row two says S1 open and S2 closed, use both settings stated in row two rather than carrying S1’s earlier closed state forward.
A sequential instruction works differently. Suppose both switches begin open; first close S1, then close S2, then open S1. In the independent two-branch circuit, the sequence is neither on, P only, both on, then Q only. Closing S2 does not automatically reopen S1, because no instruction says that it does.
A learner may get the first step right and then treat every later action as a reset of the whole circuit. Repair this by recording the complete state after each action. Only the named switch changes; other states persist unless the task explicitly resets them.
This is another reason to label inputs and outputs. “Close S2” is an action, not a full description of every switch. “S1 closed, S2 closed” is the resulting state after a particular history. The same action can produce a different outcome from a different starting state.
Worked test 14: one observation may leave two candidates alive
Candidate A has two bulbs in a single loop controlled by one switch. Candidate B has two bulbs on separate branches with a shared main switch. The only supplied observation is that both bulbs light when the switch is closed. Can that observation identify which candidate was used?
No. Both candidates predict that result under the stated working-component assumptions. Opening the shared switch also makes both bulbs go out in both candidates, so that second observation would not distinguish them either. A test is informative only when the candidate predictions differ.
A paper test that removes P while leaving all other connections as described would distinguish these two candidates: Q loses its path in A but keeps its independent branch in B. The suggestion concerns comparing the specified models, not instructing you to dismantle real electrical equipment.
Name the prediction for each candidate before proposing the test. Otherwise you may suggest another switch action that produces the same result in both and provides no new information. A good evaluation identifies what evidence would actually settle the difference.
Do not turn on-or-off evidence into an exact brightness calculation
A record that says both bulbs light establishes an on-or-off observation. It does not report their exact brightness, current or power. If the question asks only which bulb lights, keep your answer at that level. Adding an unsupported brightness ratio can weaken an otherwise correct response.
Different circuits can have complete paths while producing different currents and brightnesses. Those questions require attention to cell arrangements, bulb properties and the particular circuit relationships. Use the Primary 6 electrical-circuit concept guide for that wider topic.
The simplified assumptions at the beginning of this workshop allow us to focus on path logic. They are not a claim that every imaginable closed circuit will make any bulb visibly light with any cell. Preserve the assumptions that make a practice model useful rather than extending it beyond its purpose.
Six practice tasks: choose the decisive path
Task one: P and Q share a single loop with switches X and Y. X is closed and Y open. Predict both bulb states. A learner claims P lights because it comes before Y in the drawing. Identify the exact flaw.
Task two: two independent branches run between the cell terminals. X is in P’s branch and Y in Q’s. X is open and Y closed. Predict the bulbs. Then close X without changing Y and state the new result.
Task three: add a main switch M to the shared connection before the two branches in Task two. M is open while X and Y are closed. Can either bulb light in the stated model? Explain why the two closed branch switches are not enough.
Task four: one bulb P follows two alternative switch routes that rejoin before it, as in Test 8. The routes contain X and Y respectively. X is closed and Y open. Predict P. Then open X as well. Explain which connection becomes unavailable.
Task five: two candidate circuits both predict both bulbs on when a main switch is closed. One is a single loop and one has separate branches. Does repeating the same closed-switch observation identify the candidate? Suggest a paper comparison whose predictions differ.
Task six: both independent branch switches start open. Close X, close Y, then open X. Write the full switch state and bulb result after each action. Do not assume an unmentioned reset between actions.
Practice answers and the failed explanation
For Task one, both bulbs are off because Y breaks their shared loop. Position before the gap does not provide a complete return path. For Task two, Q alone is lit initially; after X closes, both light because both branches are complete. The open branch in the initial state did not interrupt the other branch.
For Task three, neither lights while M is open. Every route through either bulb needs the shared connection containing M. For Task four, P lights while X provides one complete alternative route, then goes out when both alternatives are open. The bulb itself remains in every completed route; the switches merely provide alternative connections before it.
For Task five, repeated agreement on the same state may confirm the record but does not separate candidates that predict the same result. Removing one bulb in the specified models distinguishes whether the other retains a complete path. State those different predictions rather than just suggesting “test again”.
For Task six, after closing X the state is X closed, Y open and P only lit. After closing Y, both switches are closed and both bulbs lit. After opening X, X is open, Y remains closed and only Q is lit. The action sequence changes one stated switch at each step.
A compact explanation that earns its conclusion
Use a clear three-part response: identify the switch state, describe which path is complete or broken, and state the bulb result. For example: “S1 is open, so P’s branch has a gap and P is off. S2 is closed and Q’s return path remains complete, so Q lights.” This is specific enough to be checked against the supplied circuit.
“Because electricity can flow” may be too vague when the question asks why one bulb lights while another does not. Name the particular path and the switch that matters. Conversely, do not add a full account of every component when the task only asks for the bulb label. Match the response length to the command while retaining the decisive reasoning when explanation is required.
After writing, trace the path described in your sentence. If the route jumps an open switch, uses an unstated junction or ignores a shared gap, revise the explanation. Checking the sentence against the circuit is more useful than checking whether it contains the words complete circuit somewhere.
Delayed transfer: change the drawing, then change the connection
First practise with a simple branch description and explicit switch labels. On a later day, redraw the same connections in a different shape or reverse the positions of the branches on the page. The results should stay the same. This tests whether the learner follows connections rather than a remembered picture.
Next move a switch from one branch to the shared connection and clearly state the change. Now its effect can extend to both bulbs. The answer should change because the circuit changed, not merely because the drawing looks different. Ask which required path now includes the relocated switch.
Finally, mix independent-trial records with sequential actions. State clearly which kind of task each is, but do not tell the learner the expected result. Look for correct state tracking and an explanation of the decisive path. A familiar circuit can still reveal a new weakness when the input format changes.
Guidance for parents and tutors
Ask the learner to trace the route before correcting the final bulb label. A wrong label can come from reversed open-and-closed meanings, an imagined junction, a missed shared switch or a carry-over mistake between trials. Each cause requires a different practice task.
Use the smallest useful prompt. “Where does this wire return?” preserves more reasoning for the learner than naming the correct bulb immediately. Once the learner can trace the route, remove the prompt and use a different switch state. A copied explanation of one state does not establish independent control of the next.
Keep real-world safety separate from paper exploration. Do not use household wiring or create direct battery short circuits to demonstrate these examples. Formal practical work should use suitable educational equipment and adult supervision under its instructions. This article’s learning goal can be met completely with written connections and labelled sketches.
Frequently asked questions
Does one open switch always turn every bulb off?
No. It turns off a bulb when it interrupts every available complete path needed by that bulb in the stated circuit. A shared switch may affect all branches; a switch on one independent branch may affect only that branch. Trace the connections before making the claim.
Does a closed switch guarantee the nearby bulb lights?
No. Another gap or open shared switch can still break the path. Physical proximity is not the connection rule. Check the entire route through the bulb to the other cell terminal under the stated working-component assumptions.
Why can two different candidate circuits fit the same result?
A limited observation may not expose their different paths. Both a single loop and parallel branches can light two bulbs when the relevant switch is closed. Select a test state in which their predictions differ rather than treating repeated agreement on one state as proof of a unique design.
Should I assume an unmentioned fault to rescue my answer?
No. If the task states that components work and gives clear connections, use that model for prediction. If supplied observations conflict and the task asks for evaluation, identify the mismatch and possible checks. Do not invent a hidden fault merely to preserve an unsupported answer.
Is an on-or-off question also a brightness question?
Not automatically. A complete-path prediction and a quantitative brightness comparison are different jobs. Use the data and assumptions required for the specific question, and avoid adding numerical claims that the observation does not provide.
Official reference and next route
The 2026 PSLE Science syllabus includes making predictions, interpreting information, evaluating observations and communicating explanations. These original circuit tests practise those reasoning jobs. They are not an official marking scheme or a forecast of particular examination questions.
Continue through the PSLE Science Learning Guide and the PSLE Learning Guide. The companion Vol 0058 overflow workshop also checks how a changed condition alters a later result, though its water model should not be treated as a complete model of electricity. Here, the final rule is to make every claimed bulb result answer to a real, complete path in the circuit you were given.
