A steel wire of length l has a magnetic moment $M$. It is bent into a semicircular arc. What is the new magnetic moment?

In figure (a), it has two concentric coils, lying in the same plane, carry current in opposite directions. The current in the larger coil $1$ is fixed. The current $i_2$ in coil $2$ can be varied. In figure (b) it gives the net magnetic moment of the two-coil system as a function of $i_2$. The vertical axis of the scale is set by ${\mu }_{net,S}=2.0\times {10}^{-5} \mathrm{A} {\mathrm{m}}^2$, and the horizontal axis scale is set by $i_{2S}=10.0 \mathrm{mA}$. If the current in coil $2$ is then reversed, what is the magnitude of the net magnetic moment of the two-coil system when $i_2=7.0 \mathrm{mA}$?

A parallel plate capacitor made of circular plates each of radius $R=6.0 \mathrm{cm}$ has a capacitance $\mathrm{C}=100 \mathrm{p}\mathrm{F}.$ The capacitor is connected to a $230 \mathrm{V}$ ac supply with an (angular) frequency of $300\text{\hspace{0.17em}rad\hspace{0.17em}}{\text{s}}^{\text{-1}}$. Determine the amplitude of $\mathrm{B}$ at a point $3.0 \mathrm{cm}$ from the axis between the plates.

What is the value of magnetic field at the center (C) of a circular loop containing two semicircles $APB$ and $AQB$as shown in the figure.

The paths of three particles A, B and C moving in a uniform magnetic field, denoted by crosses (x), are shown in the figure. The field is perpendicular to the plane of paper pointing downwards. State the nature of charge on each particle.

An ammeter and a voltmeter of suitable ranges are to be used to measure the current and voltage of an electric lamp. If a mistake were made and the meters are interchanged what will happen? Explain.