PhysicsICSE Class 8 · Electricity

Static Charge, Conduction, Induction and the Gold Leaf Electroscope (ICSE Class 8 Physics)

Updated 17 October 2026 · Fact-checked

Rubbing transfers electrons, so one body becomes negative and the other positive by equal amounts (conservation of charge). Conduction gives the same kind of charge by touching; induction, with a charged body brought near and the far end earthed, gives the opposite kind. A gold leaf electroscope detects charge because its leaves repel.

Notice the sphere ends up with the opposite charge to the rod, because the earth is removed before the rod is taken away.

Illustration drawn for QuestionBuddy.

Understand Static Charge, Charging by Conduction and Induction, Gold Leaf Electroscope

Charging by rubbing. Rubbing two different materials transfers electrons from one to the other.

The material that gains electrons becomes negative.
The material that loses electrons becomes positive, by exactly the same amount.

A glass rod rubbed with silk becomes positive (silk negative); a plastic comb rubbed in dry hair becomes negative. Like charges repel; unlike charges attract. A charged body also attracts small uncharged scraps of paper.

Conservation of charge. Charge is only transferred, never created or destroyed. If a rod loses $n$ electrons, the cloth gains the same $n$ , and the total charge before and after is the same (zero).

Charging by conduction (contact). A charged body touches an uncharged conductor and shares its charge. The conductor gets the same kind of charge as the charged body. Two identical conductors share the charge equally.

Charging by induction. No contact is needed with the charged body.
1. Bring a charged rod near (not touching) an insulated conductor. The near end gets the opposite charge and the far end the same charge.
2. Touch the far end with a finger (earth it): charge of the same kind as the rod flows to the earth.
3. Remove the earth connection first, then take the rod away.
4. The conductor is left with the opposite charge to the rod.

	Conduction	Induction
Contact with charged body	yes	no
Charge obtained	same as the charged body	opposite
Charged body loses charge	yes	no

Gold leaf electroscope. A metal cap and rod with two thin gold leaves at the bottom, inside a glass case; the rod passes through an insulating plug. Charge reaching the leaves is the same on both, so they repel and diverge.

To detect charge: a charged body touching or near the cap makes the leaves open.
To find the sign of an unknown charge, first charge the electroscope with a known sign. Then bring the unknown body near the cap. If the leaves diverge more, the unknown body has the same sign; if they collapse a little, it has the opposite sign. (Only "diverge more" is a sure test, because a very strong opposite charge can make the leaves open again.)

Lightning. A huge electric discharge between charged clouds, or between a cloud and the ground. A lightning conductor is a thick copper strip with pointed spikes on top of a tall building, running down the wall to a metal plate buried in the ground. The spikes let charge leave the air smoothly, and the strip gives the charge an easy path to the earth, so the building is not harmed.

Static Charge, Charging by Conduction and Induction, Gold Leaf Electroscope: formulas and key facts

Conservation of charge: $charge lost by one body = charge gained by the other$; Total charge before = after.
Rules of charge: Like charges repel
Unlike charges attract
A charged body attracts uncharged paper; Used for the electroscope.
Conduction and induction: Conduction: same charge by contact | Induction: opposite charge, no contact, far end earthed; Earth connection removed before the rod.

How to solve Static Charge, Charging by Conduction and Induction, Gold Leaf Electroscope questions

Track electrons: who gains them is negative, who loses them is positive, and the totals must balance.

1For rubbing, decide which body gains electrons; the other is positive by an equal amount.
2For conduction, the sign stays the same; identical bodies share equally.
3For induction, write the four steps in order: bring near, earth far end, remove earth, remove rod.
4For an electroscope, say whether the leaves diverge more or collapse, and what that shows.

Static Charge, Charging by Conduction and Induction, Gold Leaf Electroscope in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Comb and paper

Suppose you run a dry plastic comb through dry hair on a cool day and bring it near tiny pieces of paper.

Explain why the paper jumps up, and what happens to the hair.

Try it first, then show the solutionSolution

The comb gains electrons from the hair and becomes negative; the hair becomes positive by the same amount.
The charged comb attracts the neutral scraps of paper, which are lifted.

Answer: The comb is negative and attracts neutral paper; the hair is positive.

Memory hook: Charged things attract neutral scraps.

Tall tower in a storm

Imagine a tall tower has a thick copper strip running from a pointed spike at the top into a metal plate in the ground.

Why is the building not damaged when lightning strikes?

Try it first, then show the solutionSolution

The spike and strip give the charge an easy path to the earth.
The charge flows down the copper strip into the ground instead of through the building.

Answer: The lightning conductor carries the charge safely to the ground.

Memory hook: Give lightning a copper road.

Tricks to remember Static Charge, Charging by Conduction and Induction, Gold Leaf Electroscope

Short memory aids. Say each one aloud once, then use it on a question the same day.

Gain is negative
Electrons gained = negative; electrons lost = positive. "Gain gets the minus."
Use it when: Rubbing questions.
Induction: opposite, order matters
"Near, touch, take off the finger, then the rod": the earth leaves first.
Use it when: Induction steps.
Leaves repel
Same charge on both leaves, so they push apart: divergence shows charge.
Use it when: Electroscope.

Static Charge, Charging by Conduction and Induction, Gold Leaf Electroscope: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Charge on rubbed rod · 1 mark · MCQBoard level

A glass rod rubbed with silk becomes positive because:
(a) it gains protons
(b) it loses electrons
(c) it gains electrons
(d) silk gives it protons

Try it first, then show the solutionSolution

Only electrons move. The rod loses electrons, so it is positive and the silk gains them.

Answer: (b) it loses electrons

Example 2: Conservation of charge · 2 marks · Short answerBoard level

A plastic rod gains $4 \times 1 0^{10}$ electrons when rubbed with wool. (a) How many electrons does the wool lose? (b) Which body is positive? (c) Name the principle used.

Try it first, then show the solutionSolution

(a) $4 \times 1 0^{10}$ electrons, equal to the number gained. (1)
(b) The wool; (c) conservation of charge. (1)

Answer: (a) $4 \times 1 0^{10}$ (b) wool (c) conservation of charge

Example 3: Charge by induction · 4 marks · Long answerHarder board level

Describe how a metal sphere on an insulating stand can be given a negative charge using a positively charged rod, without touching the rod to the sphere.

Try it first, then show the solutionSolution

Bring the positive rod near the sphere: the near side gets negative and the far side positive. (1)
Touch the far side with a finger; electrons flow from the earth to neutralise the positive charge there. (1)
Remove the finger first. (1)
Then take the rod away: the sphere is left with a negative charge. (1)

Answer: Near, earth the far side, remove the earth, remove the rod: sphere is negative.

Example 4: Charge sharing · 3 marks · Short answerHarder board level

An insulated metal sphere A carries a charge of $- 6$ units. An identical uncharged sphere B touches it and is then separated. (a) What is the charge on each? (b) A third identical neutral sphere C touches B and is separated. What is the charge on B and C? (c) Total charge at the end?

Try it first, then show the solutionSolution

(a) Identical spheres share equally: $- 3$ and $- 3$ . (1)
(b) B and C share B's $- 3$ : $- 1.5$ each. (1)
(c) $- 3 + (- 1.5) + (- 1.5) = - 6$ , same as at the start (conservation). (1)

Answer: (a) −3 each (b) −1.5 each (c) −6 units

Example 5: Using an electroscope · 3 marks · Short answerHOTS / competency

A gold leaf electroscope is charged positively and its leaves are diverged. A charged rod is brought near the cap and the leaves (i) diverge further. A second rod brought near makes them (ii) collapse partly. State the sign of each rod and give the reasoning.

Try it first, then show the solutionSolution

(i) Leaves diverge further when more positive charge is pushed to them: the rod is positive. (1)
(ii) Leaves collapse partly when charge is attracted to the cap, leaving less on the leaves: the rod is negative. (1)
Reason: like charges repel, so the leaves, being positive, spread more with a positive rod. (1)

Answer: (i) positive (ii) negative

Where students lose marks in Static Charge, Charging by Conduction and Induction, Gold Leaf Electroscope

The slips examiners see most often, and what to write instead.

Mistake: Saying protons move when objects are rubbed
Only electrons are transferred; protons stay in the nucleus.
Wrong working
"Glass loses protons and becomes positive."
Right working
"Glass loses electrons and becomes positive."
Do this: Say "electrons" in every charging answer.
Mistake: Wrong sign by induction
Induction gives the opposite charge.
Wrong working
"Positive rod gives a positive sphere by induction."
Right working
"Positive rod gives a negative sphere by induction."
Do this: Contact: same; induction: opposite.
Mistake: Wrong order of steps in induction
The earth connection must go before the rod.
Wrong working
"Remove the rod, then lift the finger."
Right working
"Lift the finger, then remove the rod."
Do this: Memorise the order: near, earth, remove earth, remove rod.

Exam tips

Always say electrons are transferred; never say charge is created.
For induction answers, give the four steps in order and state the final sign.
Draw a labelled electroscope: cap, rod, leaves, plug and case.
In a charge-sharing question, check that the total before equals the total after.

Practice questions on Static Charge, Charging by Conduction and Induction, Gold Leaf Electroscope

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · Very short answerBoard level
State the two kinds of electric charge and the rule of attraction and repulsion between them.
Hint
Think of two rods.
Answer
Positive and negative; like charges repel, unlike charges attract.
Q2 · 2 marks · Short answerBoard level
A student charges a rod by rubbing and brings it near an uncharged electroscope; the leaves diverge. Does that prove the rod is charged? Explain what happens to the electrons in the electroscope.
Hint
Think of induction at the cap.
Answer
Yes, divergence shows charge is present. For a negative rod, electrons are pushed to the leaves (the cap becomes positive), so both leaves have the same charge and repel.
Q3 · 3 marks · Short answerHarder board level
Compare charging by conduction and by induction in three points.
Hint
Contact, sign, effect on the charged body.
Answer
Conduction: contact needed; the conductor gets the same charge; the charged body loses some charge. Induction: no contact; the conductor gets the opposite charge; the charged body does not lose charge.
Q4 · 3 marks · Short answerHarder board level
(a) Name the parts of a gold leaf electroscope. (b) Why is it made of metal inside a glass case? (c) Why does the rod pass through an insulating plug?
Hint
Conductors and insulators.
Answer
(a) Metal cap, metal rod, two gold leaves, glass case, insulating plug. (b) Metal conducts charge to the leaves; the glass case protects the thin leaves from air currents. (c) The plug stops the charge leaking to the earth through the case.
Q5 · 4 marks · Long answerHOTS / competency
A student says: "In charging by induction, the earth connection can be removed after the charged rod is taken away." Is this correct? What goes wrong? Give the correct order and also the final sign of the charge on the conductor if a negative rod is used.
Hint
What happens to the far end when the rod leaves first?
Answer
No. If the rod is removed first, the charge on the conductor redistributes and charge flows between the conductor and the earth, so the conductor ends up uncharged. Correct order: bring the rod near, earth the far end, remove the earth connection, remove the rod. With a negative rod the conductor is left positively charged.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.What moves when a body is charged by rubbing?Show answer
Electrons.
2.Sign of charge by induction?Show answer
Opposite to the charged body.
3.Why do the electroscope leaves diverge?Show answer
Both have the same charge and repel.
4.What is conserved when bodies are rubbed?Show answer
Charge.
5.Material of a lightning conductor strip?Show answer
Copper (thick metal strip).

Static Charge, Charging by Conduction and Induction, Gold Leaf Electroscope: frequently asked questions

What is the difference between charging by conduction and by induction?

In conduction the charged body touches the conductor and gives it the same kind of charge. In induction the charged body is only brought near, the far end is earthed, and the conductor is left with the opposite charge.

How does a gold leaf electroscope work?

Charge reaching the cap travels to the two gold leaves. Both get the same charge, so they repel and diverge; the more charge, the wider they open.

What is conservation of charge?

Charge cannot be created or destroyed; it is only transferred from one body to another, so the total charge stays the same.