iGCSE Physics (0625) 4.3.1 Circuit diagrams -Exam Style Questions Paper 1 - New Syllabus
▶️ Answer/Explanation
Detailed solution:
A thermistor is represented by a rectangular resistor symbol with a diagonal line that has a horizontal flat section at the bottom.
A heater is represented by a rectangular symbol containing several internal vertical lines, resembling a radiator.
In the given diagrams, the first component in circuits A and B is a variable resistor (diagonal arrow), while C and D correctly show a thermistor.
The second component in circuits A and C is a Light-Dependent Resistor (LDR), indicated by incoming arrows representing light.
Circuit D is the only option that combines the correct symbol for a thermistor with the correct symbol for a heater.
Therefore, Option D is the correct circuit diagram based on standard electrical symbols.
▶️ Answer/Explanation
Detailed solution:
The question requires identifying a pair where the first component uses a circular symbol and the second uses a rectangular one.
A motor is represented by a circle with the letter $M$ inside, satisfying the first condition.
A thermistor is represented by a rectangle with a diagonal line ending in a horizontal flat section, satisfying the second condition.
In contrast, a cell and battery use parallel lines, a switch uses broken lines, and a heater is a plain rectangle.
Therefore, the pair “motor and thermistor” correctly follows the “circle then rectangle” pattern described.
This matches Option B.
▶️ Answer/Explanation
Detailed solution:
To light only lamps P and R, current must flow through the branch containing P and R but not through the branches containing Q or S.
Closing switch 1 connects the battery to the branch with lamps P and R in series, allowing them to light.
Switches 2 and 3 control parallel paths containing lamps Q and S; leaving them open prevents Q and S from lighting.
Therefore, closing only switch 1 ensures that only lamps P and R are illuminated.
This matches Option A.