151.

In a case of infinite long wire electric field is proportional to

• $\frac{1}{\mathrm{r}}$

• $\frac{1}{{\mathrm{r}}^2}$

• $\frac{1}{{\mathrm{r}}^3}$

• r⁰

Assertion: In a cavity within a conductor, the electric field is zero.

Reason: Charges in a conductor reside only at its surface.

• If both assertion and reason are true and reason is the correct explanation of assertion

• If both assertion and reason are true but reason is not the correct explanation of assertion

• If assertion is true but reason is false

• If both assertion and reason are false

Two parallel large thin metal sheets have equal surface charge densities ( σ = 26.4 × 10^-12 C/m² ) of opposite signs. The electric field between these sheets is

• 1.5 N/C

• 1.5 × 10^-10 N/C

• 3 N/C

• 3 × 10^-10 N/C 

The spatial distribution of the electric field due to two charges (A, B) is shown in figure. Which one of the following statements is correct?

• A is +ve and +B is -ve and $\left|\mathrm{A}\right| > \left|\mathrm{B}\right|$

• A is $-$ve and B is +ve; $\left|\mathrm{A}\right| = \left|\mathrm{B}\right|$

• both are +ve but A > B

• both are $-$ve but A > B

Using mass (M), length (L), time (T ) and current (A) as fundamental quantities, the dimension of permeability is

• [ M^-1 L T^-2 A ]

• [ M L² T^-2 A^-1 ]

• [ M L T^-2A^-2 ]

• [ M L T^-1 A^-1 ]

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