
(A) The graph between magnetic susceptibility and magnetising field is as shown in (III).
(B) For \( x < a \), the magnetic field due to a current-carrying wire is given by: \[ B = \frac{\mu_0 I x}{2 \pi a^2}, \] matching graph (IV).
(C) For \( x > a \), the magnetic field due to a current-carrying wire is given by: \[ B = \frac{\mu_0 I}{2 \pi x}, \] matching graph (I).
(D) The magnetic field inside a solenoid varies with distance as shown in (II).
A thin transparent film with refractive index 1.4 is held on a circular ring of radius 1.8 cm. The fluid in the film evaporates such that transmission through the film at wavelength 560 nm goes to a minimum every 12 seconds. Assuming that the film is flat on its two sides, the rate of evaporation is:

An infinite wire has a circular bend of radius \( a \), and carrying a current \( I \) as shown in the figure. The magnitude of the magnetic field at the origin \( O \) of the arc is given by:
Let \( C_{t-1} = 28, C_t = 56 \) and \( C_{t+1} = 70 \). Let \( A(4 \cos t, 4 \sin t), B(2 \sin t, -2 \cos t) \text{ and } C(3r - n_1, r^2 - n - 1) \) be the vertices of a triangle ABC, where \( t \) is a parameter. If \( (3x - 1)^2 + (3y)^2 = \alpha \) is the locus of the centroid of triangle ABC, then \( \alpha \) equals: