磁場

The diagram shows three long straight wires $X$, $Y$ and $Z$. $X$ and $Y$ carry currents flowing into the paper while $Z$ carries a current flowing out of the paper. The currents are all equal in magnitude. What is the direction of the resultant force acting on $X$ ?

A motor lifts a load of $40$ N vertically upwards at a steady speed of $0.2\ \mathrm{m\,s^{-1}}$. The voltage applied to the motor is $12$ V and the current drawn is $2$ A. Find the efficiency of the motor.

Two long parallel wires $AB$ and $CD$ are connected to batteries as shown in the figure. The force acting on $CD$ is

In the figure shown above, a copper rod is suspended horizontally by two insulating threads $AB$ and $CD$, and the direction of the magnetic field is into the paper. What happens when the switch of the circuit is closed ?

The figure shows the path of an electron in a magnetic field $PQRS$. What should be the direction of the magnetic field ?

Two close, long, parallel, straight metal wires $X$ and $Y$ form part of the circuit shown above. $X$ and $Y$

$P$ and $Q$ are two long parallel straight wires carrying currents as shown. What is the direction of the force on $Q$ ?

The figure shows two iron rods $A$ and $B$ suspended by two light strings so that they are close together. Their lower ends are inside a solenoid. When a current flows through the solenoid, what will happen to $A$ and $B$ ?