In petrol engines, the fuel is ignited by a spark across a gap which must be les
ID: 1490197 • Letter: I
Question
In petrol engines, the fuel is ignited by a spark across a gap which must be less than about 0.60 mm. To establish the field necessary for this spark, voltages of up to 40 kV are needed, using only a 12 V battery. To achieve this, two coils are wound around the name iron core. 12 V battery. To achieve this, two coils are wound around the same iron core. The secondary coil is in series with the spark gap. The primary coil is in series with the battery and a contact breaker. When the primary circuit is broken, a spark is produced. The capacitor prevents sparking across the contact breaker. Explain why a large voltage is induced when the contact with the battery is broken.Explanation / Answer
The circuit looks like a transformer, with the single difference it's not closed. Anyway, because the coils are wound on the same iron core, the phenomenon manifests in the same way.
By breaking the contact with the battery, a variable current crosses the primary coil. This creates a variable magnetic flux through the primary coil, which, in its turn, creates a (variable) current, thus, a voltage, in the secondary circuit/coil.
It's the electromagnetic induction phenomenon.
I hope it's helpful.