Page 38 - Physics_Form_2

Physics for Secondary Schools

Task 1.3

Construct a proof plane using
materials such as aluminium foil, Convective
clouds
a small piece of cardboard, and a
FOR ONLINE READING ONLY
wooden stick. Once constructed,
use the proof plane in conjunction
with a leaf electroscope to determine Air currents
the sign of the charge on a charged
object. Figure 1.44: Positively and negatively

charged clouds
Lightning and thunderstorms As charge builds up beyond a certain

Lightning, a dramatic electrostatic limit, the insulating property of the
phenomenon, results from charge medium between positive and negative
separation within storm clouds. Ice charge centre breaks down. Hence, a
crystals and water droplets collide, large current suddenly passes, ionising
creating positive and negative charges that the air molecules on its way, accompanied
segregate. A stepped leader, an ionised by the sudden expansion of the air. The
air channel, descends from the cloud, ionisation of air results in the observed
meeting a positive charge rising from the flash of light (lightning), as shown in
ground. This interaction forms the return Figure 1.45. Sudden expansion results in
stroke, the visible lightning flash. The the booming sound (thunder) that is heard
rapid heating of air by lightning causes its a few seconds after the flash is seen.
expansion, resulting in the sound waves
we recognise as thunder. The process
occurs in milliseconds.

Lightning is a large spark due to
electrostatic discharge within a cloud,
between two clouds or between a cloud
and the ground. Interaction between
updrafts and downdrafts in the cloud
produces static charge by friction. The
lower portion of the cloud becomes Figure1.45: Lightning
negatively charged, and the upper
part is positively charged. The ground
beneath the cloud can become positively Thunderstorms are intense weather
charged by induction. Figure 1.44 shows conditions characterised by lightning,
positively and negatively charged clouds. heavy rain, and powerful winds.

32
Student’s Book Form Two

Physics Form 2 Final.indd 32 25/10/2025 10:25