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CIE iGCSE Co-Ordinated Science P4.5.4 Force on a current-carrying conductor Exam Style Questions Paper 3

CIE iGCSE Co-Ordinated Science Paper 3 - All Chapters

Question

Fig. 9.1 shows a washing machine.
(a)(i) The washing machine uses:
• a heater to heat the water
• a motor to pump the hot water through the machine.
The motor and the heater are connected in a parallel circuit. The motor and the heater are each operated by separate switches.
The circuit symbol for a heater is
The circuit symbol for a motor is
Fig. 9.2 shows an incomplete circuit diagram for the washing machine.
Complete the circuit diagram on Fig. 9.2.
(ii) The resistance of the heater is \(20 \, \Omega\).
The resistance of the motor is \(80 \, \Omega\).
Identify from the list the most likely value for the combined resistance of the heater and motor connected in parallel.
Explain your answer.
16 Ω       20 Ω       50 Ω       80 Ω       100 Ω
(iii) The current in the wires of the electrical circuit is a flow of charged particles. State the name of the particles that flow in the wires of the electrical circuit.
(iv) The current-carrying coil in the motor experiences a turning effect.
This turning effect can be increased by increasing the number of turns on the coil.
State two other ways to increase this turning effect.
(b) Inside the washing machine, some of the water evaporates.
During evaporation, water changes state from a liquid to a gas.
(i) Complete the diagrams in Fig. 9.3 to show the arrangement and separation of molecules in a liquid and in a gas.
(ii) During evaporation, the water does not boil. State the boiling point of water.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic P4.3.1 — Circuit diagrams and circuit components (Part (a)(i))
• Topic P4.2.4 — Resistance (Part (a)(ii))
• Topic P4.2.2 — Electric current (Part (a)(iii))
• Topic P4.5.4 — Force on a current-carrying conductor (Part (a)(iv))
• Topic P2.1.2 — Particle model (Part (b)(i))
• Topic P2.2.2 — Melting, boiling and evaporation (Part (b)(ii))

▶️ Answer/Explanation

(a)(i) heater and motor in parallel, each with its own switch

The heater and motor are drawn as two separate parallel branches connected across the 240 V supply.
Each branch contains its own switch in series with the heater or motor component.

(a)(ii) 16 Ω

For resistors in parallel, the combined resistance is always less than the smallest individual resistance.
Since the smallest resistance here is \(20\,\Omega\), the combined resistance must be less than \(20\,\Omega\), so \(16\,\Omega\) is the only possible value from the list.

(a)(iii) electrons

The current in metal wires is a flow of free/delocalised electrons.

(a)(iv) increase the current; increase the strength of the magnetic field

Increasing the current flowing through the coil increases the turning effect (torque).
Using a stronger magnet increases the strength of the magnetic field, which also increases the turning effect.

(b)(i) liquid: molecules touching, randomly arranged; gas: molecules widely separated, randomly arranged

In the liquid box, molecules should be drawn touching each other but in a random (not regular) arrangement.
In the gas box, molecules should be drawn much further apart (no more than about seven molecules), moving randomly.

(b)(ii) 100 °C

The boiling point of water at standard atmospheric pressure is \(100\,^{\circ}\text{C}\).

Question

(a) Table 9.1 contains descriptions of a solid, a liquid and a gas.
Complete Table 9.1 using the words in the list.
solid         liquid         gas
Use each word once only.
(b) Some water is heated in a copper saucepan on the hot-plate of an electric cooker. This is shown in Fig. 9.1.
(i) State the main method of thermal energy transfer through:
    the copper saucepan 
    the water. 
(ii) Suggest why the handle of the saucepan is made from plastic and not copper.
(c) An electric circuit contains a copper wire.
The current in the copper wire is 0.5 A.
The potential difference (p.d.) across the copper wire is 4.0 V.
Calculate the resistance of the wire.
State the unit of your answer.
(d) Fig. 9.2 shows a copper wire placed between the poles of a magnet.
When the switch is closed, the wire moves upwards.
State how this observation would change if the current is reversed.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C1.1 — States of matter (Part (a))
• Topic P2.3.4 — Consequences of thermal energy transfer (Part (b))
• Topic P4.2.4 — Resistance (Part (c))
• Topic P4.5.4 — Force on a current-carrying conductor (Part (d))

▶️ Answer/Explanation

(a) Random and close = liquid; regular and close = solid; random and widely separated = gas

In a liquid, particles are close together but can move past one another, giving a random arrangement.
In a solid, particles are close together in a fixed, regular arrangement, while in a gas they are far apart and move randomly.

(b)(i) Copper saucepan: conduction; water: convection

Heat travels through the solid copper saucepan by conduction, as vibrating particles pass energy to neighbouring particles.
Heat travels through the water by convection, as warmer, less dense water rises and cooler water sinks, setting up a circulating current.

(b)(ii) Plastic is an insulator

Plastic is a poor conductor of heat, unlike copper which conducts heat very well.
Using plastic for the handle keeps it cool enough to hold safely.

(c) 8 Ω

Using Ohm’s law, \( R = \frac{V}{I} \).
\( R = \frac{4.0}{0.5} = 8 \, \Omega \).

(d) The wire moves downwards/the opposite way

The direction of the force on a current-carrying wire in a magnetic field depends on the direction of the current.
Reversing the current reverses the direction of the force, so the wire moves downwards instead of upwards.

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