Which instrument converts mechanical energy to electrical energy?

$(a)$ Describe an activity to show the pattern of magnetic field lines of a bar magnet,with the help of a cardboard piece and iron filings.
$(b)$ Compare the magnetic field of a bar magnet with that of a current-carrying solenoid with the help of a figure.

$(a)$ What is meant by a 'magnetic field'?
$(b)$ How is the direction of magnetic field at a point determined?
$(c)$ Describe an activity to demonstrate the direction of the magnetic field generated around a current-carrying conductor.
$(d)$ What is the direction of the magnetic field at the centre of a current-carrying circular loop?

The phenomenon of electromagnetic induction is:

Commercial electric motors do not use

Describe the working of an $AC$ generator with the help of a labelled circuit diagram. What changes must be made in the arrangement to convert it to a $DC$ generator?