Question

Brush your hair with a plastic comb. Bring the comb close to a small piece of paper. Move a fridge magnet near the comb and then the paper. Do these objects exert forces on one another? Observation and explain scientific principles please.

Answer 1

On brushing hair with a plastic comb, ststic charges are created due to friction. Force will exist between the following pairs :

a. Comb and magnet- Due to relatic motion between the two, we can consider the "ststic" charges on the comb to be moving with respect to the magnet. Magnetic field exert a force called on moving charges. This force is given by

F_m= qvB, where q is the charge, v is the velocity of the charge and B is the magnetic field in the region.

This can alternatively be understood by considering the displacement current associated with the flux created by moving charges. Moving charges create a time varying electric flux. This creates a magnetic field just like the one created by the fridge magnet. Hence they will attract or repel just like two magnets would do.

b. Comb and paper- The static charges on the comb create an electric field around the comb. Paper is not a conductor but can be considered as a dielectric which gets polarised (charge separation) when the comb comes close to it. Considering comb to be negatively charged it creates a positive polarity at the closer end of the paper. This is termed INDUCTION of charge. Hrence the two attract each other.