Sec 4 Physics Static Electricity topical questions

A polythene rod is rubbed with a dry cloth. State the charge on the rod and on the cloth, and explain both in terms of electron transfer.

Define an electric field and state two rules for drawing electric field lines.

State the difference between a conductor and an insulator in terms of electron movement, and give one example of each.

Explain, in terms of charge, why a rubbed comb picks up small neutral pieces of paper.

State what happens to the leaf of a charged electroscope when a finger touches the metal cap, and explain why.

An insulated metal sphere hangs from a nylon thread.

1. (a)Describe how to charge the sphere positively by induction using a negatively charged polythene rod, naming each step in order.[4]
2. (b)State the final charge on the sphere and compare it with the rod’s charge.[2]

Sketches (described in words) of field-line patterns are needed for four cases: an isolated positive charge; an isolated negative charge; a positive and negative pair; two like positive charges.

1. (a)Describe the pattern for each isolated charge.[2]
2. (b)Describe the pattern between the +/− pair.[2]
3. (c)Describe the pattern between the two like charges and name the special point between them.[2]

A gold-leaf electroscope is charged negatively by touching it with a charged rod.

1. (a)Explain why the leaf rises during the contact.[2]
2. (b)The electroscope stays deflected after the rod is removed. What does this show, and why?[2]
3. (c)A positively charged rod is now brought near the cap without touching. State what happens to the leaf and explain.[2]

A tanker truck delivers fuel to a petrol station.

1. (a)Explain how the flowing fuel generates static charge.[2]
2. (b)Explain the danger if the truck is not bonded to the storage tank.[2]
3. (c)State how bonding and earthing remove the danger.[2]

A student charges an electroscope negatively, then brings a charged rod of unknown sign slowly toward the cap from a distance.

1. (a)The leaf rises further as the rod approaches. State the sign of the rod and justify it.[3]
2. (b)State what would have been observed instead if the rod carried the opposite sign, and why.[3]
3. (c)The student now touches the cap with a finger while the rod in (a) is nearby. Predict the leaf behaviour on removing the finger and then the rod.[2]

A photocopier drum is coated with a photoconductive surface that holds charge in the dark but conducts where light strikes.

1. (a)Describe how the drum carries a charged image of the document.[3]
2. (b)Explain how toner ends up on the paper in the shape of the image.[3]
3. (c)State one similarity and one difference between a photocopier and an electrostatic precipitator.[2]

Two insulated conducting spheres, P and Q, hang touching each other on nylon threads. A student performs the two-sphere induction sequence with a positively charged rod near P.

1. (a)State the charge on the near face of P and on the far side of Q while the rod is present.[2]
2. (b)The spheres are separated while the rod remains, and the rod is then removed. State the final charge on each sphere.[2]
3. (c)Explain why the spheres must be conductors and why the threads are nylon.[4]

Lightning strikes a tall building protected by a lightning rod connected to thick copper cable running to the ground.

1. (a)Explain how charge separation builds in a storm cloud and induces charge on the building.[3]
2. (b)Explain why the strike usually attaches to the rod rather than the roof.[3]
3. (c)State why the cable to earth is made thick copper.[2]