G9S1M2 REvision

The diagram shows two light, silver-coated balls labeled X and Y hanging from threads near to each other.

Which line identifies the possible charges on X and Y?

• X- neutral

  Y - neutral

• X- negative

  Y - negative

• X- negative

  Y - positive

• X- positive

  Y - negative

Answer explanation

Law of Charges:

Like charges repel

Unlike charges attract

A student wants to charge up some rods by rubbing them with a cloth made from a suitable material.

He has a number of rods to choose from: a copper rod, a PVC rod, an aluminium rod and a glass rod.

Which two of the rods would hold a charge when rubbed with an appropriate cloth?

• Aluminium and PVC

• Glass and Copper

• Aluminium and Copper

• Glass and PVC

Answer explanation

Charging by Friction is only possible for INSULATORS.

A PVC (plastic) rod is rubbed with a nylon cloth. This process causes electrons to be transferred between the rod and the cloth, causing both objects to become charged.

Which of the rows in the table correctly gives the nature of the charges on both the cloth and the rod, and the effect the objects have on each other after becoming charged?

• Charges on rod and cloth (the same)

  effect (repel)

• Charges on rod and cloth (the same)

  effect (attract)

• Charges on rod and cloth (opposite)

  effect (repel)

• Charges on rod and cloth (opposite)

  effect (attract)

Answer explanation

Charging both INSULATORS will always create oppositely charged object. Which makes both objects attracted to each other.

What is the definition of an electric field?

• A region in space in which a mass experiences a force due to the Earth’s mass.

• A region in space through which electromagnetic radiation is passing.

• A region in space in which a compass needle experiences a force.

• A region in space in which an electric charge experiences a force.

Answer explanation

Electric field is very similar to gravitational field. You cannot see it, but you can feel its effect on objects.

A student rubs a polythene rod with a cloth, giving it a negative charge. She then holds it near an earthed, conducing sphere as shown in the diagrams below.

Which of the diagrams shows the correct distribution of charges on the conducting sphere?

• 
• 
• 
• 

Answer explanation

The positive charges goes near the negatively charged rod while the electrons are discharged to the earth.

The student then holds the plastic rod near a stream of water coming from a tap. The stream of water bends towards the plastic rod.

Which pictures below show the correct arrangement of charges in the stream of water?

• 
• 
• 
• 

Answer explanation

The positve charges in the stream of water are attracted to the negatively charged rod, therfore it bends towards the rod.

Which of the following pairs of charges shows the correct electric force between them?

• 
• 
• 
• 

A man pushes a metal trolley along a corridor toward a lift.

The trolly has nylon wheels and the floor of the corridor is covered with plastic.

The man wears shoes with rubber soles. As he moves the trolley, the man gains an electric charge. Explain how the man gains an electric charge

• Through the friction between nylon wheels and the plastic floor.

• Through the conduction between nylon wheels and the plastic floor

• Through the friction between the rubber shoes and the plastic floor.

• Through the conduction between the rubber shoes and the plastic floor.

A student holds a roll of sticky tape and pulls the end down as shown in the diagram.

This causes both the roll and the end of the tape to become electrically charged by friction. Explain how an object becomes charged by friction.

• Conduction transfers electrons making both objects oppositely charged.

• Tape gains electrons due to friction while the hand loses electrons

• Electron exchange via friction makes both objects similar in charge

• Conduction causes tape (negative) and hand (positive) charges.

Which of these non-metals can conduct electricity?

• Carbon

• Chalk

• Plastic

• Rubber