Static electricity and electric fieldsIB MYP Physics: Subtopic test

1. 1
   A student in a school laboratory rubs a dry polythene rod with a woollen cloth. Afterwards the rod is able to pick up small scraps of paper. Careful tests show that the rod has become negatively charged and the cloth has become positively charged.

   (a)

   Which particles are transferred between the cloth and the rod when the rod is rubbed?

   [1 mark]

   • AProtons
   • BElectrons
   • CNeutrons
   • DPositive ions

   (b)

   The rod is hung from an insulating thread. A second polythene rod, rubbed in exactly the same way, is brought close to it. Which statement is correct?

   [1 mark]

   • AThe rods attract because like charges attract.
   • BThe rods attract because the thread is an insulator.
   • CThe rods repel because both carry the same type of charge.
   • DThe rods repel because one rod is a conductor.

   (c)

   Explain why the polythene rod becomes negatively charged when it is rubbed with the cloth.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   At an airport, a fuel tanker pumps aviation fuel into an aircraft through a long rubber hose. As the fuel rushes through the hose, friction makes charge build up on the hose and the tanker. Before pumping begins, a thick metal cable is clipped from the tanker to the aircraft, and a second cable connects the aircraft to the ground.

   (a)

   What is the main purpose of the metal cables?

   [1 mark]

   • ATo let charge flow safely to earth so it cannot build up
   • BTo make the fuel flow faster through the hose
   • CTo store extra charge on the tanker
   • DTo make the aircraft positively charged

   (b)

   Why are the cables made of metal rather than plastic?

   [1 mark]

   • AMetals have more protons than plastics
   • BMetals are insulators, so they stop charge moving
   • CPlastics are always heavier than metals
   • DMetals are conductors, containing electrons that are free to move

   (c)

   Explain why a spark between the tanker and the aircraft would be dangerous if the cables were not used.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A group of students investigate how the number of times a polythene rod is rubbed with a woollen cloth affects the amount of charge the rod gains. After rubbing, they touch the rod to the metal cap of a gold-leaf electroscope and use a protractor to measure how far the gold leaf rises away from the metal stem. The electroscope is discharged by touching the cap before every trial.

   (a)

   Identify the independent variable, the dependent variable and one control variable in this investigation.

   [3 marks]

   (b)

   The students recorded these angles: 5 rubs gave 10°, 10 rubs gave 22°, 15 rubs gave 31° and 20 rubs gave 33°. Describe the trend in the results, explain why the gold leaf rises, and suggest one way to make the results more reliable.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A car-parts factory currently paints metal bumpers with ordinary spray guns, and much of the paint misses the bumper and is wasted. The company is considering switching to electrostatic paint spraying. In this method each paint droplet is given an electric charge as it leaves the nozzle, and the metal bumper is given the opposite charge.

   (a)

   Explain how electrostatic spraying coats the bumper evenly with little wasted paint. Refer to the electric field in your answer.

   [6 marks]

   (b)

   The factory uses solvent-based paint, which gives off flammable vapour. Evaluate whether the company should switch to electrostatic spraying.

   [6 marks]

   Total for question 4: 12 marks

End of questions