1. 1
   A student rubs an acetate rod with a silk cloth for several seconds. During rubbing, electrons transfer from the acetate rod to the silk cloth.

   (a)

   What charge does the acetate rod gain as a result of losing electrons to the silk cloth?

   [1 mark]

   • APositive, because it now has more protons than electrons
   • BNegative, because it has more electrons than protons
   • CNeutral, because charge is conserved overall
   • DNegative, because it has gained electrons

   (b)

   What charge does the silk cloth gain?

   [1 mark]

   • APositive, because it has lost electrons
   • BNegative, because it has gained electrons from the rod
   • CNeutral, because friction does not transfer charge
   • DPositive, because it has gained protons

   (c)

   Explain, in terms of electrons, why the acetate rod becomes positively charged when rubbed with the silk cloth.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A teacher rubs two identical acetate strips with a silk cloth, giving each strip a positive charge, and hangs them close together from insulating threads so they can swing freely.

   (a)

   What happens when the two positively charged acetate strips are brought close together?

   [1 mark]

   • AThey attract, because like charges always attract
   • BThey attract, because opposite charges attract
   • CThey repel, because like charges repel each other
   • DNothing happens, because both strips have the same charge and cancel out

   (b)

   The teacher then brings a negatively charged rubber rod close to one of the hanging strips without touching it. What is observed?

   [1 mark]

   • AThe rubber rod repels the hanging strip, since they carry opposite charges
   • BNothing happens, since the rod does not touch the strip
   • CThe hanging strip loses its charge instantly
   • DThe rubber rod attracts the hanging strip, since they carry opposite charges

   (c)

   Explain, in terms of charge, why two strips carrying the same type of charge repel each other when brought close together.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A person walks across a synthetic carpet in dry conditions, and their body becomes electrically charged through friction with the carpet. When they then touch a metal door handle, they feel a small electric shock as a spark jumps between their finger and the handle.

   (a)

   Explain, in terms of electrons, how the person's body becomes electrically charged as they walk across the carpet.

   [3 marks]

   (b)

   Explain why a spark occurs when the charged person's finger approaches the metal door handle, and explain how earthing the door handle helps to prevent a dangerous build-up of charge on it in the first place.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A technician assembles delicate electronic circuit boards in a factory. While moving around on the vinyl floor, static charge can build up on the technician's body through friction with clothing and shoes. To prevent this charge from damaging the sensitive microchips, the technician wears a wrist strap connected by a conducting wire to a metal plate embedded in the earthed workbench.

   (a)

   Explain how the wrist strap and earthed workbench prevent a dangerous build-up of static charge on the technician's body, and explain, using the idea of an electric field, why a charged technician touching a microchip directly (without the strap) could damage it even without a visible spark.

   [6 marks]

   (b)

   The workbench's metal plate is connected to earth using a wire of very low resistance. Explain why earthing works effectively as a safety and protection measure in this situation, and describe, using the idea of an electric field around a point charge, how you would expect the field to change if the technician's body charge (while not wearing the strap) became larger over time.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A student runs a plastic comb through her clean, dry hair several times. During this process, electrons transfer from her hair to the comb.

   (a)

   What charge does the comb gain from this process?

   [1 mark]

   • ANegative, because it has gained electrons
   • BPositive, because it has lost electrons
   • CNeutral, because friction cannot charge insulators
   • DPositive, because it has gained protons

   (b)

   The student then holds the charged comb close to (but not touching) some small pieces of tissue paper on the table. What happens?

   [1 mark]

   • ANothing, since the comb must touch the paper to have any effect
   • BThe paper pieces are attracted to the comb, due to induced charge separation within the paper
   • CThe paper pieces are repelled from the comb, since like charges repel
   • DThe paper pieces become permanently charged with the opposite charge to the comb

   (c)

   Explain, in terms of induced charge, why the small, uncharged pieces of tissue paper are attracted to the charged comb even though they are not directly touching it.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   Two small metal spheres, A and B, are mounted on insulating stands. Sphere A is given a positive charge and sphere B is given a negative charge, then they are brought close together without touching.

   (a)

   What happens to spheres A and B when they are brought close together?

   [1 mark]

   • AThey repel, since sphere A is positive and sphere B is negative
   • BThey repel, since both were charged by the same process
   • CThey attract, since they carry opposite (unlike) charges
   • DNothing happens, since metal cannot hold static charge

   (b)

   The spheres are then touched together briefly and separated again. What is most likely to happen to their charges?

   [1 mark]

   • ABoth remain exactly as charged as before, since touching has no effect on charge
   • BSphere A becomes more positive and sphere B becomes more negative
   • CBoth spheres lose all their charge to the surrounding air instantly
   • DCharge flows between the spheres until they reach a similar (possibly neutral or reduced) charge, since the touching allows electrons to transfer

   (c)

   Explain, in terms of electrons, what happens when the oppositely charged spheres A and B are briefly touched together.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   In a flour mill, fine flour dust is blown through metal pipework at high speed to move it between machines. The friction between the moving dust particles and the inside of the pipe can cause a build-up of static charge on the ungrounded metal pipework, creating a risk that a spark could ignite the flour dust suspended in the air.

   (a)

   Explain, in terms of friction and charge transfer, how static charge builds up on the inside of the metal pipework as flour dust is blown through it.

   [3 marks]

   (b)

   Explain why this build-up of charge on the pipework is particularly dangerous in a flour mill, and explain how earthing the pipework would reduce this danger.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   In a school science demonstration, a Van de Graaff generator builds up a large positive charge on its metal dome. A student stands on an insulated stool and places one hand flat on the dome. As charge flows onto her, individual strands of her hair are seen to stand up and spread apart from each other.

   (a)

   Explain, in terms of charge and the forces between charges, why the student's hair strands spread apart and stand on end once she is charged by the dome, and explain why she must stand on an insulated stool for this demonstration to work.

   [6 marks]

   (b)

   Explain, using the idea of an electric field, what happens in the space around the student's charged body while she remains on the insulated stool, and explain what would happen, in terms of a spark, if another person standing on the earthed floor slowly brought a finger close to (but not touching) the student's charged hand.

   [6 marks]

   Total for question 8: 12 marks

End of questions