151.

The capacity of an air condenser is 2.0 µF. If a medium is placed between its plates, the capacity becomes 12 μF. The
dielectric constant of the medium will be

• 5

• 4

• 3

• 6

Taking the earth to be a spherical conductor of diameter 12.8×10³ km. Its capacity will be

• 711 μF

• 611 μF

• 811 μF

• 511 μF

 A charge Q is distributed uniformly in a sphere (solid). Then, the electric field at any point r,  where, r < R (r is the radius of sphere) varies as:

• ${\mathrm{r}}^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}$

• r ^-1

• r

• r ^-2

As per this diagram a point charge +q is placed at the origin O. Work done in taking another point charge -Q from the point A [coordinates (O, a)] to another point B [coordinates (a, O)] along the straight path AB is

• zero

• $\left(\frac{-\mathrm{qQ}}{4{\mathrm{\pi \epsilon }}_{\mathrm{o}}} \frac{1}{{\mathrm{a}}^2}\right) \sqrt{2}\mathrm{a}$

• $\left(\frac{\mathrm{qQ}}{4{\mathrm{\pi \epsilon }}_{\mathrm{o}}} \frac{1}{{\mathrm{a}}^2}\right)$

• $\left(\frac{\mathrm{qQ}}{4{\mathrm{\pi \epsilon }}_{\mathrm{o}}} \frac{1}{{\mathrm{a}}^2}\right)\sqrt{2}\mathrm{a}$

A charged particle (charge q) is moving in a circle of radius R with uniform speed v. The associated magnetic moments given by

• $\frac{\mathrm{q} \mathrm{\nu } \mathrm{R}}{2}$

• qνR²

• $\frac{\mathrm{q} \mathrm{\nu } {\mathrm{R}}^2}{2}$

• qνR

A steady current of 1.5 A flows through a copper voltameter for 10 min. If the electrochemical equivalent of copper is 30x 10^-5 g C^-1 , the mass of copper deposited on the electrode will be

• 0.40 g

• 0.50 g

• 0.67 g

• 0.27 g

When a charged particle moving with velocity $\overrightarrow{\mathrm{v}}$is subjected to a magnetic field of $\overrightarrow{\mathrm{B}}$ induction , the force on it is non- zero. This implies that

• angle between $\overrightarrow{\mathrm{v}} \mathrm{and} \overrightarrow{\mathrm{B}}$ is necessarily 90^o

• angle between $\overrightarrow{\mathrm{v}} \mathrm{and} \overrightarrow{\mathrm{B}}$ can have any value other than 90^o

• angle between $\overrightarrow{\mathrm{v}} \mathrm{and} \overrightarrow{\mathrm{B}}$ can have any value other than 180^o

• angle between $\overrightarrow{\mathrm{v}} \mathrm{and} \overrightarrow{\mathrm{B}}$ is either zero or 180^o

What is not true for equipotential surface for uniform electric field?

• Equipotential surface is flat

• Equipotential surface is spherical

• Electric lines are perpendicular to equipotential surface 

• Work done is zero

A capacitor having capacitance 1 uF with air, is filled with two dielectrics as shown. How many times capacitance will increase

• 12

• 6

• 8/3

• 3

Figure shows three spherical and equipotential surfaces A, B and C round a point charge q. The potential difference ${\mathrm{V}}_{\mathrm{A}} - {\mathrm{V}}_{\mathrm{B}} = {\mathrm{V}}_{\mathrm{B}} -{\mathrm{V}}_{\mathrm{C}}$ If t₁ and t₂ be the distances between them, then              

• t₁ = t₂

• t₁ > t₂

• t₁ < t₂

• t₁ ≤ t₂