A laboratory technician needs to give a metal can a charge without letting the charged object touch the can. Fig. 1 shows the first stage. A positively char...
Question 1 Report
A laboratory technician needs to give a metal can a charge without letting the charged object touch the can. Fig. 1 shows the first stage. A positively charged strip is held beside the can, while an Earth wire can be connected to the far side. The technician uses a plastic handle so that charge does not pass through their hand. The aim is for the can to remain charged after the strip has been removed.
Fig. 1
(a) Describe the movement of electrons in the can when the positive strip is brought near it. [2]
(b) State the order of the next three actions needed to leave the can charged: remove the Earth wire, connect the Earth wire, remove the positive strip. [3]
(c) Explain why the can has a negative charge at the end of the process. [3]
(d) State why the technician uses a plastic handle. [1]
Answer Details
(a) Electrons in the metal can move towards the positively charged strip. The near side becomes negative, leaving the far side positive. This redistribution is electrostatic induction. [2]
(b) The required order is:
- Connect the Earth wire.
- Remove the Earth wire while the positive strip is still near.
- Remove the positive strip.
This order is essential because it traps the transferred electrons on the can. [3]
(c) While the can is earthed, electrons flow from Earth into the can, attracted by the nearby positive strip. The Earth wire is removed before these electrons can flow back. The can is left with extra electrons and therefore a net negative charge. [3]
(d) Plastic is an insulator, so it prevents charge flowing through the technician's hand to Earth. [1]
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