電荷與靜電（卷二）：練習題

Which of the following statements best explains why a metal rod held in a person's hand cannot be easily charged by rubbing it with a cloth?

In the first stage of the photocopying process, a selenium-coated drum is given a uniform positive charge in the dark. When an image of the document is projected onto the drum, what happens to the charge in the areas hit by light?

Which of the following describes a fundamental difference between an electrical conductor and an electrical insulator?

The drum of a photocopier is coated with selenium, which acts as a photoconductor. During the copying process, which of the following describes the behavior of the electrostatic charge on the drum when it is exposed to light?

A student brings a negatively charged plastic rod close to the metal cap of an uncharged gold leaf electroscope. The gold leaves are observed to diverge. Which statement correctly explains why the leaves diverge?

Two identical balloons are suspended by insulating threads. After both balloons are rubbed with the same piece of dry fur, they are brought close to each other. Describe the observed interaction and state the physics principle that explains this behavior.

Industrial chimneys use electrostatic precipitators to remove ash particles from smoke. The ash particles first pass through a highly charged negative grid and then travel between grounded metal collecting plates. Explain how the ash particles are separated from the smoke and collected.

A student rubs a copper rod with a woollen cloth while holding the rod in their bare hand. Explain, in terms of electron mobility, why the copper rod does not appear to become charged.

In an inkjet printer, small droplets of ink are used to form characters on paper.

(a) Each droplet is given a specific amount of electrostatic charge before passing between two parallel metal plates. Explain the purpose of these plates and how they influence the path of the droplets. (3)

(b) Some droplets are not given any charge. Describe the resulting path of these uncharged droplets. (1)

A student uses a polythene rod and a dry cloth to investigate electrostatic phenomena.

(a) The student rubs the polythene rod with the cloth. Explain, in terms of electrons, how the rod becomes negatively charged. (2)

(b) The rod is then held near a thin stream of water from a tap. The stream of water is seen to bend towards the rod.
(i) State whether the water is an electrical conductor or an insulator. (1)
(ii) Explain why the stream of water is attracted to the negatively charged rod. (2)

(c) Electrostatic charges can be dangerous when fuelling an aircraft. Explain how a spark could be produced during the fuelling process and why this is a safety hazard. (3)