(i) Magnetic field pattern of a current-carrying circular loop:
The magnetic field lines appear as concentric circles around each part of the wire. As we move towards the centre of the loop, these arcs become larger and appear as straight parallel lines at the centre. (Student should draw a circular loop with field lines entering from one face and exiting from the other, appearing as straight lines at the centre.)
(ii) Direction of magnetic field — Right-Hand Thumb Rule:
Imagine holding the current-carrying conductor in the right hand with the thumb pointing in the direction of current. The fingers curling around the conductor give the direction of the magnetic field. Applying this to each section of the loop, all sections contribute to the field in the same direction inside the loop.
(iii) Reasons:
(I) Fuse of identical rating only:
A fuse of higher rating would allow excess current to flow, failing to protect the circuit during short-circuiting or overloading, which may damage appliances or cause fire. Only an identical-rated fuse provides correct protection.
(II) Soft iron core in electromagnet:
Soft iron can be magnetised and demagnetised quickly and easily. It retains the magnetic property only as long as current flows, making it ideal for an electromagnet that needs to be switched on and off.
Source: Chapter 12 — Magnetic Effects of Electric Current, Sections 12.2.3, 12.2.2, and What You Have Learnt
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