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.

Figure shows a point P near a long conductor XY carrying a current I. MN is a short current-carrying conductor kept at the point P parallel to the conductor XY. What is the direction of the force experienced by the conductor MN due to the current flowing through XY?

Two long wires carrying current $I_1$ and $I_2$ are arranged as shown in figure. The one carrying current $I_1$ is along the $x$-axis. The other carrying current $I_2$ is along a line parallel to the $y$-axis given by $x=0$ and $z=d$. Find the force exerted at $O_2$ because of the wire along the $x$-axis.