In a cathode ray tube, a potential difference of 3000 volts is maintained between the deflector plates whose separation is $$2 \mathrm{~cm}$$. A magnetic field of $$2.5 \times 10^{-3} \mathrm{~Wb} / \mathrm{m}^2$$ at right angles to electric field gives no deflection of the electron beam, which received an initial acceleration by a potential difference of $$10000 \mathrm{~V}$$. Calculate $$(\mathrm{e} / \mathrm{m})$$ of an electron.
A wire of cross-section $$A$$ is stretched horizontally between two clamps located $$2 l$$ metre apart. A weight $$w \mathrm{~kg}$$ is suspended from the mid-point of the wire. If the mid-point sags vertically through a distance $$x<1$$, the strain produced is
A stream of electrons is projected horizontally to the right. A straight conductor carrying, a current is supported parallel to the electron stream and above it. If the current in the conductor is from left to right, what will be the effect on the electron stream?
A bar magnet suspended by a horse's hair lies in the magnetic meridian where there is no twist in the hair, on turning the upper end of the hair through $$150^{\circ}$$, the magnet is deflected through $$30^{\circ}$$ from the meridian. Then the angle through which upper end of the hair has to be twisted to deflect the magnet through $$90^{\circ}$$ from the meridian is