This diagram shows the structure of a spark plug in an internal combustion engine. The magnified section shows the end of the spark plug, with some of the lines of force representing the electric field.

i. Copy the field lines from the diagram. On your copy, draw arrows on the lines of force to show the direction of the field.
ii. What evidence does the diagram give that the field is strongest near the tip of the inner electrode?
b. The gap between the inner and outer electrodes is 1.25 mm and a field strength of 5.0 × 10⁶ N C⁻¹ is required for electrical breakdown. Estimate the minimum potential difference that must be applied across the inner and outer electrodes for a spark to be produced. (You may treat the two electrodes as a pair of parallel plates.)
c. When an electron is accelerated through a potential drop of approximately 20 V it will have sufficient energy to ionise a nitrogen atom. Show that an electron must move 4.0 μm to gain this energy.

Transcribed Image Text:

insulator inner electrode outer electrode field lines (screws into engine block) gap between inner and other electrodes Figure 1 Figure 2 Figure 21.20