1. 1
   At a school science fair, a student rubs a balloon vigorously on her wool jumper and finds that the charged balloon then sticks to a wall and attracts her hair.

   (a)

   What actually happens between the balloon and the jumper as she rubs them together?

   [1 mark]

   • AProtons are transferred from the jumper to the balloon
   • BElectrons are transferred between the jumper and the balloon
   • CNeutrons are transferred from the balloon to the jumper
   • DWhole atoms are transferred between the two surfaces

   (b)

   After rubbing, the balloon becomes negatively charged and the jumper becomes positively charged. If the student now holds the balloon close to her jumper, what will happen?

   [1 mark]

   • AThey will repel each other, since both are charged
   • BThey will exchange charge instantly and become neutral
   • CNothing will happen, since charge only affects hair
   • DThey will attract each other, since they carry opposite charges

   (c)

   Describe a simple experiment the student could use to detect and confirm that the balloon has become electrostatically charged after rubbing it on the jumper.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Before a fuel tanker is filled with petrol at a depot, workers attach a metal earthing strap between the tanker and the ground to allow any static charge to flow away safely and prevent a spark from igniting fuel vapour.

   (a)

   Before a fuel tanker is filled at a depot, workers attach a metal earthing strap between the tanker and the ground to prevent a static spark from igniting fuel vapour. The earthing strap is made of copper. Why is copper suitable for this safety purpose?

   [1 mark]

   • ACopper is an electrical insulator, so it stores charge safely
   • BCopper is magnetic and attracts stray charge
   • CCopper is an electrical conductor, allowing charge to flow away to the ground
   • DCopper is transparent, so workers can see the charge

   (b)

   If a positive charge builds up on the metal surface of the tanker, in which direction does the electric field point at a point just outside the tanker's surface?

   [1 mark]

   • AIn the direction of the force that would act on a positive charge placed at that point
   • BIn the direction of the force that would act on a negative charge placed at that point
   • CAlways parallel to the ground, regardless of the charge
   • DElectric fields only exist inside conductors, not outside them

   (c)

   Using a simple electron model, explain why copper allows charge to flow away through the earthing strap but the rubber tyres of the tanker do not.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A museum's science gallery displays a large Van de Graaff generator, which builds up a substantial positive charge, measured in coulombs, on its smooth metal dome for visitor demonstrations.

   (a)

   A museum's science gallery displays a Van de Graaff generator, which builds up a large positive charge, measured in coulombs, on its metal dome. Describe the pattern of the electric field around the isolated charged dome, and state how the field pattern would differ around a single small isolated point charge of the same sign.

   [3 marks]

   (b)

   For a separate demonstration, museum staff connect the dome to one of two flat metal plates held parallel and close together, giving one plate a positive charge and the other an equal negative charge. Describe the pattern of the electric field between the two oppositely charged parallel plates, and state the unit in which the total charge on each plate is measured.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   During a thunderstorm, strong air currents inside a storm cloud cause ice crystals and water droplets to collide and rub against each other, transferring charge so that the base of the cloud becomes negatively charged while the upper part becomes positively charged, eventually leading to a lightning strike to the ground.

   (a)

   Explain, in terms of electron transfer, the forces between charges, and electric fields, how this charge separation leads to a large electric field building up between the cloud base and the ground, eventually resulting in a lightning strike.

   [6 marks]

   (b)

   Tall buildings are fitted with a lightning conductor: a pointed metal rod at the highest point of the building, connected by a thick copper cable running down the outside wall to a metal plate buried in the ground. Explain, using ideas about conductors and insulators, electric fields, and forces between charges, how this lightning conductor protects the building during a thunderstorm.

   [6 marks]

   Total for question 4: 12 marks

End of questions