(a) Sometimes, due to faulty wires, the insulation breaks and the live wire comes in contact with the body of the appliance. If the appliance is earthed, the charge flows to the each and protects us from electric shock.
(b) The maximum value of current is determined by the thickness of the main live wire

Since the two cells are connected with the positive terminal in one side. This can be corrected by joining the negative terminal of one cell to the positive terminal of other cell as shown in figure.

When current is passed through a coil of wire then the coil behaves like a magnet. One end of coil acts as north pole and other end acts as south pole When the electric current is swithed off, the coil generally loses its magnetism. Such coils are called electromagnets. The electromagnets are very strong and their power can be increased so they are very important.
Two important applications (uses)of electromagnets are:
(i)They are used in electric bells, telegraphs telephones and speakers etc 
(ii) They are used in cranes to lift heavy loads of scrap iron or iron sheets

Overloading can be avoided if too many appliances are not connected to a single socket. Short circuiting is a name given to a situation in which the live and the neutral wires accidently come in contact.
Electric fuse is a safety device. When a short circuit takes place or when overloading takes place, then the current becomes large and heats the fuse wire too much and thus, it gets melted and circuit breaks which prevents the damage of the wiring and electrical appliances.

MCBs (Miniature circuit breakers) are switches which automatically turn off when current in a circuit exceeds the safe limit. We turn them on and the circuit is once again complete