12. Consider a conducting loop of radius a and total loop resistance R placed in a region with a magnetic field B thereby enclosing a flux $${\phi _0}$$ . The loop is connected to an electronic circuit as shown, the capacitor being initially uncharged.

If the loop is pulled out of the region of the magnetic field at a constant speed u, the final output voltage Vout is independent of

If the loop is pulled out of the region of the magnetic field at a constant speed u, the final output voltage Vout is independent of
13. A conducting sphere of radius R is placed in uniform electric field $${\overrightarrow {\bf{E}} _0}$$ directed along +Z-axis. The electric potential for outside points is given as $${V_{{\text{out}}}} = - {E_0}\left( {1 - \frac{{{R^3}}}{{{r^3}}}} \right)r\cos \theta ,$$ where r is the distance from the centre and θ is the polar angle. The charge density on the surface of the sphere is
14. A laser beam of wavelength 600 nm with a circular cross-section having a radius of 10 mm fails normally on a lens of radius 20 mm and focal length 10 cm. The radius of the focussed spot is approximately
15. A current $$l$$ flows in the anticlockwise direction through a square loop of side a lying in the XOY plane with its centre at the origin. The magnetic induction at the centre of the square loop is
16. The electric (E) and magnetic (B) field amplitudes associated with an electromagnetic radiation from a point source behave at a distance r from the source as
17. An electron is accelerated from rest by 10.2 millionvolt. The percent increase in its mass is
18. A toroidal coil has N closely-wound turns. Assume the current through the coil to be $$l$$ and the toroid is filled with a magnetic material of relative permittivity $${\mu _r}.$$ The magnitude of magnetic induction $$\overrightarrow {\bf{B}} $$ inside the toroid, at a radial distance r from the axis, is given by
19. A particle of charge q, mass m and linear momentum $$\overrightarrow {\bf{p}} $$ enters an electromagnetic field of vector potential $$\overrightarrow {\bf{A}} $$ and scalar potential $$\phi .$$ The Hamiltonian of the particle is
20. Two magnetic dipoles of magnitude m each are placed in a plane as shown below. The energy of interaction is given by
