As shown in the figure, the work done to move the charge ' $Q$ ' from point $C$ to point $D$ along the semicircle CRD is

The length and area of cross-section of a copper wire are respectively 30 m and $6 \times 10^{-7} \mathrm{~m}^2$. If the resistivity of copper is $1.7 \times 10^{-8} \Omega \mathrm{~m}$, then the resistance of the wire is

If current of 80 A is passing through a straight conductor of length 10 m , then the total momentum of electrons in the conductor is

(mass of electron $=9.1 \times 10^{-31} \mathrm{~kg}$ and charge of electron $=1.6 \times 10^{-19} \mathrm{C}$ )

In a wire of radius 1 mm a steady current of 2 A uniformly distributed across the cross-section of the wire is flowing. Then the magnetic field at a point 0.25 mm from the centre of the wire is