Two spherical conductors B and C having equal radii and carrying equal charges in them repel each other with a force F when kept apart at some distance. A third spherical conductor having same radius as that of B but uncharged, is brought in contact with B, then brought in contact with C and finally removed away from both. The new force of repulsion between B and C is

• $\frac{\mathrm{F}}{4}$

• $\frac{3 \mathrm{F}}{4}$

• $\frac{\mathrm{F}}{8}$

• $\frac{3 \mathrm{F}}{8}$

A charge q is located at the centre of a cube. The electric flux through any face is

• $\frac{4 \mathrm{\pi q}}{6 \left(4{\mathrm{\pi \epsilon }}_{\mathrm{o}}\right)}$

• $\frac{\mathrm{\pi q}}{6 \left(4{\mathrm{\pi \epsilon }}_{\mathrm{o}}\right)}$

• $\frac{\mathrm{q}}{6 \left(4{\mathrm{\pi \epsilon }}_{\mathrm{o}}\right)}$

• $\frac{2\mathrm{\pi q}}{6 \left(4{\mathrm{\pi \epsilon }}_{\mathrm{o}}\right)}$

Three equal charges, each having a magnitude of 2.0 x 10^-6 C, are placed at the three corners of a right angled triangle of sides  3 cm,  4 cm  and  5 cm. The force (in magnitude) on the charge at the right angled corner is

• 50 N

• 26 N

• 29 N

• 45.9 N

Two charges of + 10 μC and +20 μC are separated by a distance 2 cm. The net potential (electric) due to the pair at the middle point of the line joining the two changes, is

• 27 MV

• 18 MV

• 20 MV

• 23 MV

25.

The charges on two spheres are + 7 µC and -5C respectively. They experience a force F. If each of them is given an additional charge of -2 µC, then the new force of attraction will

• F

• $\frac{\mathrm{F}}{2}$

• $\frac{\mathrm{F}}{\sqrt{3}}$

• 2F

A square loop ABCD, carrying a current I₂, is placed near and coplanar with a long straight conductor XY carrying a current I₁, as shown in figure. The net force on the loop will be

• $\frac{{\mathrm{\mu }}_0 {\mathrm{I}}_1 {\mathrm{I}}_2}{2 \mathrm{\pi }}$

• $\frac{{\mathrm{\mu }}_0 {\mathrm{I}}_1{\mathrm{I}}_2 \mathrm{L}}{2 \mathrm{\pi }}$

• $\frac{2 {\mathrm{\mu }}_0 {\mathrm{I}}_1{\mathrm{I}}_2 \mathrm{L}}{3 \mathrm{\pi }}$

• $\frac{2{\mathrm{\mu }}_0 {\mathrm{I}}_1 {\mathrm{I}}_2}{3 \mathrm{\pi }}$

Three identical charges are placed at the vertices of an equilateral triangle. The force experienced by each charge, ( if k = 1/4$\mathrm{\pi } {\mathrm{\epsilon }}_0$ ) is

• $2\mathrm{k} \frac{{\mathrm{q}}^2}{{\mathrm{r}}^2}$

• $\frac{\mathrm{k} {\mathrm{q}}^2}{2 {\mathrm{r}}^2}$

• $\sqrt{3} \mathrm{k} \frac{{\mathrm{q}}^2}{{\mathrm{r}}^2}$

• $\frac{\mathrm{k} {\mathrm{q}}^2}{\sqrt{2} {\mathrm{r}}^2}$

The angle of dip at a certain place where the horizontal and vertical components of the earth's magnetic field are equal is

• 30^o

• 75^o

• 60^o

• 45^o

Assertion:  Lines of force are perpendicular to conductor surface.

Reason:  Generally electric field is perpendicular to equipotential 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.

The force per unit length between two straight conductors separated by a distance of 0.02 m is 2 x 10^-3 N m^-1. The current in one conductor is 10 A and that in the other conductor is

• 20 A

• 5 A

• 2 A

• 10 A