You Asked:

How does a spark plug use voltage to ignite a spark in car engines? — Sumitha, Tirupur, India

Marshall Brain Answers:

A spark plug is an incredibly simple device at the core. It is basically 2 wires with a little air gap between them. One of the wires is connected to ground (the negative side of the battery in this case) through the engine block. The other wire receives a pulse of high voltage electricity. A visible spark forms in the gap, and this spark ignites the gasoline.

This video shows you where the high voltage electricity comes from. There is a coil – essentially a transformer – that steps up the voltage from 12 volts to 50,000 to 100,000 volts:

The voltage has to be high in order to jump across the air gap. Essentially the spark is like a tiny bolt of lightning.