1) Explain why an atom is neutral
2) A teacher rubs a Perspex rode with a cloth. It becomes charged.
a) What is the net charge on the cloth?
b) What is the net charge on the rod?
c) Would the rod attract or repel a charged polythene rod? Explain your answer.
3) Why can plastic become charged if you rub it, but not metal?
4) A student says that the rods repel because they have poles like magnets. Is she correct? Explain your answer.
Answers
Answer1: When an atom has an equal number of electrons and protons, it has an equal number of negative electric charges (the electrons) and positive electric charges (the protons). The total electric charge of the atom is therefore zero and the atom is said to be neutral.
Answer2: when a piece of Perspex is rubbed with a cloth it becomes positively charged. Electrons have been rubbed from the Perspex onto the cloth. Again, the rod and the cloth have opposite charges and will attract each other.
Answer3: When you rub plastic, you transfer electrons from one material to the other. ... Because plastic is an insulator, the electrons cannot flow through it so they effectively get stuck there - they are static. In a metal, the electrons would get conducted away (e.g. back to the material they have come from).
Answer4: She is not correct, The rods are repelled or attracted because they have become electrically charged.11