How does a car make the spark and power its electrical equipment?
The vehicle electrical system - battery, alternator, starter motor - and the ignition system that makes the high-voltage spark via the coil and spark plugs.
A CCEA GCSE Motor Vehicle and Road User Studies answer on the vehicle electrical system - battery, alternator and starter motor - and the ignition system that makes the spark using the coil and spark plugs.
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What this dot point is asking
CCEA wants you to know the vehicle electrical system - the battery, alternator and starter motor - and the ignition system that makes the spark using the coil and spark plugs. The specimen paper directly asks "what is the purpose of the coil in the ignition system?" and "how is electrical power delivered to the spark plugs?", so this is core content.
The answer
The electrical system
A car needs electricity to start the engine, make the spark, and run the lights, wipers, indicators and other equipment.
The system also includes fuses (which protect circuits by melting if too much current flows) and the wiring that connects everything.
The ignition system
The ignition system's job is to produce a spark in each cylinder at exactly the right moment to ignite the air-fuel mixture.
The high-voltage pulse must reach the correct cylinder at the correct time:
- Older systems use a distributor to send the spark to each plug in turn.
- Modern systems use electronic ignition controlled by the engine management system, with no distributor.
The spark fires at the end of the compression stroke, igniting the mixture to start the power stroke.
How it fits the four-stroke cycle
The ignition is timed so the spark occurs just as the piston nears the top of the compression stroke, so the burning gases push the piston down with full force on the power stroke. Correct ignition timing is essential for smooth, efficient running.
Worked example: the car will not start
Examples in context
Example 1. The alternator warning light. A battery-shaped warning light usually means the alternator is not charging, so the car is running off the battery alone and will soon stop.
Example 2. Worn spark plugs. Old, worn spark plugs give a weak spark, causing misfires and poor starting - which is why plugs are replaced at a service.
Try this
Q1. What is the purpose of the ignition coil? [1 mark]
- Cue. To step up the battery's low voltage to the high voltage needed to make a spark.
Q2. Which part generates electricity to recharge the battery while the engine runs? [1 mark]
- Cue. The alternator.
Q3. What does the starter motor do? [1 mark]
- Cue. Turns the engine over (cranks it) to get it started.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA style4 marksDescribe the job of (a) the battery, (b) the alternator and (c) the starter motor in a vehicle's electrical system.Show worked answer →
(a) The battery stores electrical energy and supplies it to start the engine and run the electrics (lights, ignition, etc.) when the engine is not running.
(b) The alternator is driven by the engine and generates electricity while the engine runs, recharging the battery and powering the electrics.
(c) The starter motor is a powerful electric motor that turns the engine over (cranks the crankshaft) to get it started, drawing a large current from the battery.
Markers reward: battery stores/supplies electricity, alternator generates electricity/recharges the battery, starter motor turns the engine to start it.
CCEA style4 marksExplain how the ignition system produces a spark at the spark plug, naming the part that raises the voltage and stating how the spark reaches the right cylinder.Show worked answer →
The ignition coil takes the low voltage (about 12 V) from the battery and steps it up to the very high voltage (thousands of volts) needed to make a spark jump across the spark plug gap.
The high-voltage pulse is delivered to the correct cylinder at the correct time - in older systems by the distributor, in modern systems by electronic ignition controlled by the engine management system - so the spark fires at the end of the compression stroke. The spark ignites the air-fuel mixture, starting the power stroke.
Markers reward: coil raises 12 V to a high voltage, the spark jumps the plug gap, delivered to the right cylinder at the right time (distributor/electronic), igniting the mixture.
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