From the figure find the capacitance of the capacitor?

42.

Two spheres of same metal have radii a and b. Thet have been connected to a conducting wire. Find the ratio of the electric field intensity upon them.

• a/b

• b/a

• b² / a

• b²/a²

If in a circuit current lags behind EMF by  $\frac{\mathrm{\pi }}{2}$. Then it is a/an

• resistor circuit

• capacitor

• inductor circuit

• CR circuit

X-ray beam are affected by

• electric field

• magnetic field

• both (a) and (b)

• none of these

If a unit positive charge is taken from one point to another over an equipotential surface, then

• work is done on the charge

• work is done by the charge

• work done is constant

• no work is done

Figure shows the electric lines of forces emerging from a charged body. If the electric field at A and B are E_A and  E_B respectively and if the displacement between A and B is r, then

• E_A > E_B

• E_A < E_B

• E_A = E_B/r

• E_A = E_B / r²

$\frac{\mathrm{Q}}{{\mathrm{\epsilon }}_{\mathrm{o}}}$

• $\frac{\mathrm{Q}}{6{\mathrm{\epsilon }}_{\mathrm{o}}}$

• $\frac{\mathrm{Q}}{6 {\mathrm{\epsilon }}_{\mathrm{o}}}$

• $\frac{\mathrm{Q}}{{\mathrm{\epsilon }}_{\mathrm{o}} {\mathrm{a}}^2}$

• $\frac{\mathrm{Q}}{4{\mathrm{\pi \epsilon }}_{\mathrm{o}}{\mathrm{a}}^2}$

A small piece of metal wire is dragged across the gap between the pole pieces of a magnet in 0.4 sec. If magnetic flux between the pole pieces is known to be 8 × 10^-4 Wb, then induced emf in the wire, is

• 4 × 10^-3 V

• 8 × 10^-3 V 

• 20 × 10^-3 V

• 6 × 10^-3 V

Two coherent monochromatic light beams of amplitude 3 and 5 units are superposed. The maximum and minimum possible intensities in the resulting beams are in the ratio

• 4 : 2

• 16 : 1

• 8 : 2

• 4 : 2

Colour of star depends upon

• luminosity

• temperature

• brightness

• all of these