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In a solenoid, the current flowing through the circuit generates its own magnetic field. Hence the electrical energy of the circuit is converted to magnetic field.

(ii)-(b) The bar will be magnetised as long as there is current in the circuit.

The magnetic field produced by the solenoid will be reinforced by the iron bar and it will be magnetised as long as there is current in the circuit.

(iii)-(a) A bar magnet

Solenoids mimic bar magnets. The magnetic field of a solenoid are similar to that of a bar magnet and just like a bar magnet the a solenoid also has north and south poles.

(iv)-(d) Only II

As can be seen from the graph the magnetic field is increasing linearly with current. Therefore, the current is directly proportional to the magnetic field.

(v)-(a) For a current of 0.8A the magnetic field is 13 mT

From the above graph we can see that 0.8 A corresponds to 13 mT magnetic field.