Question

If you accumulate a static charge and then touch a wooden frame of a door, you often find no spark or shock, although there would be if you touched the metal handle. Why?

Answer 1

Hint: The shock or spark that occurs in a material is due to the jumping of charged particles from one object to another. It is to neutralise the excess charge in the former substance. For such a flow to occur the material should be allowed to pass charges.

Complete answer:
We know that conductors are materials which allow charges to pass through them, whereas insulators do not allow current to pass. We can insulate or accumulate a charge on an insulator due to this property of the insulators. We have done several experiments in our school in which we accumulate charges on plastic scales or combs to attract bits of papers. This is possible only with insulators as they do not allow the charges to pass through them. If we consider a metal conductor, instead of the plastic scale in our experiments we will be disappointed.
Now, we have understood that conductors let charges to spread and pass through them, whereas the insulators do not. Consider the given situation, where we bring a charge to a metal and a wooden frame.
We observe sparks or a bit of electric shock when we touch the metal with the charge. This is due to the jumping of the excess charge from the accumulated body to the metal body which is a better conductor. This neutralisation of charges produces spark or shock.
When we touch the wooden frame with the same charge, we observe nothing. This is because the wood is an insulator and doesn’t allow the electricity to pass through it.

Note:
We can do the ‘magic’ trick with plastic objects because the insulators help accumulate charge on them without getting distributed in them and getting ‘earthed’. The metals are good conductors which allows the charges to be neutralised and earthed.
Earthing is the process by which the excess charges from a material are passed to the earth to maintain their neutrality.