Two identical charged spheres suspended from a common point by two massless strings of lengths l, are initially at a distance d (d << 1) apart because of their mutual repulsion. The charges begin to leak from both the spheres at a constant rate. As a result, the spheres approach each other with a velocity v. Then, v varies as a function of the distance x between the sphere, as

1. VX

2. V

3. V 

4. V 

A positively charged ball hangs from a silk thread. We put a positive test charge q₀ at a point and measure F/q₀, then it can be predicted that the electric field strength E 

(1) > F/q₀

(2) = F/q₀

(3) < F/q₀

(4) Cannot be estimated

The dielectric constant of pure water is 81. Its permittivity will be 

(1) 7.17 × 10^–10 MKS units

(2) 8.86 × 10^–12 MKS units

(3) 1.02 × 10¹³ MKS units

(4) Cannot be calculated

A charge q is placed at the centre of the open end of the cylindrical vessel. The flux of the electric field through the surface of the vessel is 

(1) Zero

(2) $\frac{q}{{\epsilon }_0}$

(3) $\frac{q}{2{\epsilon }_0}$

(4) $\frac{2q}{{\epsilon }_0}$ 

There is a uniform electric field of strength 10³ V/m along the y-axis. A body of mass 1g and charge 10^–6C is projected into the field from the origin along the positive x-axis with a velocity 10m/s. Its speed in m/s after 10s is (Neglect gravitation) 

(1) 10

(2) $5\sqrt{2}$

(3) $10\sqrt{2}$

(4) 20

Four-point +ve charges of the same magnitude (Q) are placed at four corners of a rigid square frame as shown in the figure. The plane of the frame is perpendicular to Z-axis. If a –ve point charge is placed at a distance z away from the above frame (z<<L) then 

(1) – ve charge oscillates along the Z-axis.

(2) It moves away from the frame

(3) It moves slowly towards the frame and stays in the plane of the frame

(4) It passes through the frame only once.

X and Y are large, parallel conducting plates close to each other. Each face has an area A. X is given a charge Q. Y is without any charge. Point A, B, and C are as shown in the figure. Find the incorrect option.

1.  the field at B is $\frac{\mathrm{Q}}{2{\mathrm{\epsilon }}_0\mathrm{A}}$

2.  the field at B is $\frac{\mathrm{Q}}{{\mathrm{\epsilon }}_0\mathrm{A}}$

3.  the fields at A, B and C are of the same magnitude

4.  the fields at A and C are of the same magnitude but in opposite directions

A point charge q is placed at a distance a/2 directly above the centre of a square of side a. The electric flux through the square is:

1. $\frac{q}{{\epsilon }_0}$

2. $\frac{q}{\pi {\epsilon }_0}$

3. $\frac{q}{4{\epsilon }_0}$ 

4. $\frac{q}{6{\epsilon }_0}$

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

(1) Only -q is in stable equilibrium

(2) None of the charges are in equilibrium

(3) All the charges are in unstable equilibrium

(4) All the charges are in stable equilibrium

Two-point charges +q and –q are held fixed at (–d, 0) and (d, 0) respectively of a (x, y) coordinate system. Then 

(1) E at all points on the y-axis is along $\hat{i}$

(2) The electric field $\overrightarrow{E}$ at all points on the x-axis has the same direction

(3) Dipole moment is 2qd directed along $\hat{i}$

(4) Work has to be done in bringing a test charge from infinity to the origin