(a) Describe the distribution of charge on

a metal conductor before touching P

and after touching P

Answers

Before touching P: Positive charges

are induced on the inside part of

conductor, P and negative charges are

to the outside part of conductor, P.

After touching P: The negative

charges on the ball, B neutralizes the

positive charges on the inside part of

the conductor, P. therefore,

conductor, P remains with no charge

inside.

When the sphere is moved on different

positions inside the pall without touching it,

the divergence does not change

When the positive sphere touches the pall,

the induced negative charges of the pall

neutralize the sphere. The net charge

remains outside the sphere, this shows that

no charge resides inside the hollow

conductor.

(b) After touching conductor P, the ball is

transferred into a positively charged

electroscope and tested for its charge.

State and explain what is observed?

Answer

There was no change in divergence of

the gold leaf because the ball, B had

lost its charge due to neutralization

when it touched conductor, P.

Example 02

State and explain the observation on the leaf

of a positively charged electroscope when a

negatively charged rod is brought close to its

cap as shown below.

Example 01

The figure below shows a negatively

charged ball B, inside a metal conductor P.

Answer

The leaf collapses: This is because, when a

negatively charged rod was brought near the

cap of the electroscope, it induced positive

charges at the cap and repelled negative

charges down to the plate and the gold leaf

leading to neutralization of the positive

charges thus the gold leaf collapses.

A highly charged positive point is brought

close to a Bunsen burner flame. State and

explain what will be observed.

Answer

The flame is blown away from the sharp

point:

ACTION AT SHARP POINTS

Due to high charge density around the sharp

point, the air around the sharp point is

ionized forming positive and negative ions.

Negative ions are attracted to the sharp point

and positive ions are repelled away from the

sharp point forming an electric wind which

blows the candle flame.

The sharp points of a conductor have a high

charge density which creates a strong

electric field. The strong electric field

ionizes the air around the sharp points

forming positive and negative ions.

Ions which have the same charge as that on

the sharp points are repelled away and ions

which have an opposite charge to that on the

sharp points are attracted towards the sharp

points resulting into neutralization of charge

hence corona discharge.

LIGHTNING AND LIGHTINING

CONDUCTOR

Lightning: is a large spark due to

electrostatic discharge within a cloud,

between two clouds or between a cloud and

the ground.

Corona discharge (charge leakage) is the

process by which a pointed conductor

apparently loses its charge.

Mechanism

Note that” The repelled ions from the sharp

points form an electric wind which can blow

a candle flame as shown below.

Interaction between up-drifts and down-

drifts in the cloud produces static charge by

friction. The lower portion of the cloud

becomes negatively charged and the upper

part positively charged. The ground beneath

the clouds becomes positively charged.

Application of action at sharp points

(corona discharge):

(i) Used in a lightning conductor

(ii) Used in electrostatic generators e.g Van

de Graaff generator

(iii) Used in electrostatic photocopying

machines.

As the charge build up beyond a certain

limit, the insulating property of the medium

between positive and negative charges

breaks down. Hence, a large current

suddenly passes, ionizing the air molecules

Example 01

on its way, accompanied by sudden

expansion of air.

1.50 LIGHTINING AND

THUNDERSORMS

The ionization of air results in the observed

flush of light (lighting) and the sudden

expansion results into the booming sound

(thunder) that is heard a few second after the

flash is seen.

Lightning is a large spark due to

electrostatic discharge within a cloud,

between two clouds or between a cloud and

the ground.

Formation f lightning

Interaction between updrafts and

downdrafts in the clouds produces static

charges by friction.

The lower portion of the cloud becomes

negatively charged, and the upper part is

positively charged. The ground beneath the

cloud can be positively charged by

induction.

Radar: is a zigzag path followed by

electrons from the negative cloud to the

positive cloud across the air during the

lightning process.

Thunder is an audible sound produced due

to bombardment of air molecules during

lightning

Thunderstorm

Thunderstorm is severe weather associated

with Lightning and thunder, heavy rainfall

and strong winds.

Fig: A positively and negatively charged

clouds

As the charge builds up beyond a certain

limit, the insulating property of the medium

between positive and negative charge centre

breaks down.

Points to note:

The current flow and heating effect of

Lightning can cause destruction of property

and life. A single discharge of Lightning

can lead to a temperature as high as

30 000℃.

Hence, a large current suddenly passes,

ionizing the air molecules on its way,

accompanied by sudden expansion of the

air.

Sharp or pointed objects on the earth’s

surface such as mountains, trees and tall

houses are highly charged and therefore

prone to lightning strikes. Therefore, if you

are caught outside during lightning, you are

advised to stay at low areas in ground

example in ditches.

The ionization of the air results in the

observed flash of light (lightning) and the

sudden expansion results in the booming

sound (thunder) that is heard a few seconds

after the flash is seen.

travel safely to the ground, thereby

preventing damage to the building

A lighting conductor is a sharp ended metal

rod attached to a building and connected to a

thick copper strip that leads into the ground

to protect the building from lightning

strikes.

The lightning conductor should be taller

than the house protected. When the lightning

strikes the conductor, the electric charges

flow along the wire and are dissipated to the

ground, where they cause no harm and

thereby protect the building.

Thunderstorms are intense weather

conditions characterized by lightning, heavy

rain, and powerful winds.

NB: Lightning, a dramatic electrostatic

phenomenon, results from charge separation

within storm clouds.

Mode of action of lighting conductor

A negatively charged cloud passing

overhead causes the sharp spikes of the

conductor to become positively charged by

induction. The acquired charge on the spikes

is safely conducted to the ground; hence, no

lightning occurs, and no harm is caused to

the building

Ice crystals and water droplets collide,

creating positive and negative charges that

segregate. A stepped leader, an ionizing air

channel, descends from the clouds, meeting

a positive charge from the ground. This

interaction creates a return stroke, visible

lighting flash.

The rapid heating of air by lightning causes

the air to expand, resulting in the sound

waves we recognize as thunder.

LIGHTNING PROTECTION

Lightning cannot be prevented, but

protection against destruction is possible by

using lightning conductors.

A lightning conductor works because the

charge concentrates more on sharp points,

such as mountains, trees, and tall houses.

The sharp points have high density of charge

so; they are liable to be struck by lightning.

A lighting conductor is a metal rod,

Points to note:

typically made of copper, installed atop a

structure to protect it from lightning strikes.

If there is huge discharge, the air ionizes to

form positive and negative charges which

neutralize the charges on the spikes. Hence

NB: It offers a low – resistance path for the

electrical current of a lightning strike to