Three long straight wires are carrying current as shown in the diagram. The magnetic force per unit length on wire $Q$ is $..... \times 10^{-7} \ N/m$.

Give the uses of electromagnets.

$A$ horizontal semi-circular wire of radius $r$ is connected to a battery through two similar springs $X$ and $Y$. The battery sends a current $I$ through the wire. $A$ uniform magnetic field $B$ is applied perpendicular to the plane of the wire, as shown in the figure. What is the force acting on each spring?

$A$ wire loop of irregular shape carrying current is placed in an external magnetic field. If the wire is flexible,the shape of the loop changes to

$A$ single turn current loop in the shape of a right-angled triangle with sides $5\,cm$,$12\,cm$,and $13\,cm$ carries a current of $2\,A$. The loop is placed in a uniform magnetic field of magnitude $0.75\,T$,whose direction is parallel to the current in the $13\,cm$ side of the loop. The magnitude of the magnetic force on the $5\,cm$ side is $\frac{x}{130}\,N$. The value of $x$ is $..........$

In the figure,the cube has an edge length of $40\,cm$. Four straight segments of wire $ab$,$bc$,$cd$,and $da$ form a closed loop that carries a current $I = 5\,A$. $A$ uniform magnetic field of $0.02\,T$ is in the $+y$-direction. The ratio of the magnetic force on segment $ab$ to the magnetic force on segment $bc$ is: