51.

Length cannot be measure by

• fermi

• micron

• debye

• light year

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

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

A Gaussian sphere encloses an electric dipole within it. The total flux across the sphere is

• zero

• half that due to a single charge

• double that due to a single charge

• dependent on the position of the dipole

The specific charge of a proton is 9.6 x10⁷ C kg^-1  The specific charge of an alpha particle will be

• 9.6 x10⁷ C kg^-1

• 19.2 x10⁷ C kg^-1

• 4.8 x10⁷ C kg^-1

• 2.4 x10⁷ C kg^-1

Point charges + 4q, - q and+ 4q are kept on the x-axis at points x = 0, x = a and x = 2a respectively, then

• only- q is in stable equilibrium

• all the charges are in stable equilibrium

• all the charges are in unstable equilibrium

• none of the above

If E_a be the electric field strength of a short dipole at a point on its axial line and E_e that on equilateral line at the same distance, then

• E_e = 2E_a

• E_a = 2E_e

• E_a = E_e

• none of these

Charges 4Q, q and Q are placed along x-axis at positions x = 0, x = l/2 and x = l, respectively. Find the value of q so that the force on charge Q is zero:

• Q

• $\frac{\mathrm{Q}}{2}$

• $-\frac{\mathrm{Q}}{2}$

• -Q