Which year was the first successful transatlantic telegraph cable laid?

Obtain the expression for the fringe width of interference fringes in Young's Double slit experiment.

Derive the expression for the intensity at a point where interference of light occurs. Arrive at the conditions for maximum and zero intensity.

A square loop of side $\text{'}\mathrm{a}\text{'}$ carrying a current ${\mathrm{I}}_2$ is kept at distance $\mathrm{x}$ from an infinitely long straight wire carrying a current ${\mathrm{I}}_1$ as shown in the figure. Obtain the expression for the resultant force acting on the loop.

Choose the correct answer from the options given below:

Using Kirchhoff$\text{'}$s rules, calculate the current through the $40 \mathrm{\Omega }$ and $20 \mathrm{\Omega }$ resistors in the following circuit$:$

An arrangement of three parallel straight wires placed perpendicular to plane of paper carrying same current $I$ along the same direction is shown in Figure. Magnitude of force per unit length on the middle wire $B$ is given by