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Charge on the move

Aim

To reinforce what you have learned about conduction electrons.

1Complete the following sentences using words from the list below.

charge electrons positive negative

a)An electric current is a flow of charge carried by electrons which move round the circuit from the negative terminal of the battery to the positive terminal.

b)A metal contains electrons that can move about freely inside the metal. A metal object can only hold charge if it is insulated from the ground.

c)When two oppositely charged metal objects are brought into contact, electrons transfer from the negative object to the positive object.

2Figure 1 shows an electroscope. State and explain what happens to the electroscope when a negatively charged object is brought near to its cap.

The leaf goes up because electrons transfer to it from the cap due to the force of repulsion on them from the charged rod.

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Figure 1

3Figure 2 shows the location of the charged atoms in an insulated metal object when a negatively charged rod is brought near to it.

a)The conduction electrons in the object moved from the left-hand side of the object to the right-hand side when the negatively charged rod was brought near the object.

i)Why did the charged rod cause the conduction electrons to move to the other end?

The electrons were repelled by the rod because they have the same type of charge as the rod.

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ii)Why did the transfer of the conduction electrons in the object make the one end positive and the other end negative?

Electrons in the object were forced away from the rod because the rod has the same type of charge as the electrons. So the end of the object near the rod lost electrons and became positive; the other end became negative because it gained electrons

b)In terms of electron transfer, explain why the insulated object would become charged negative overall if the rod touched the object?

Electrons would transfer from the negative ions on the rod to the object so the object would become negatively charged overall.