If an insulated non-conducting sphere of radius R has charge density ρ. The electric field at a distance r from the centre of sphere (r < R) will be 

(1) $\frac{\rho R}{3{\epsilon }_0}$

(2) $\frac{\rho r}{{\epsilon }_0}$

(3) $\frac{\rho r}{3{\epsilon }_0}$

(4) $\frac{3\rho R}{{\epsilon }_0}$ 

Infinite charges of magnitude q each are lying at x =1, 2, 4, 8... meter on X-axis. The value of the intensity of the electric field at point x = 0 due to these charges will be 

(1) 12 × 10⁹q N/C

(2) Zero

(3) 6 × 10⁹q N/C

(4) 4 × 10⁹q N/C

A pendulum bob of mass $30.7\times {10}^{-6}kg$ and carrying a charge $2\times {10}^{-8}C$ is at rest in a horizontal uniform electric field of 20000 V/m. The tension in the thread of the pendulum is $(g=9.8m/s^2)$

(1) $3\times {10}^{-4}N$

(2) $4\times {10}^{-4}N$

(3) $5\times {10}^{-4}N$

(4) $6\times {10}^{-4}N$ 

A charged ball \(B\) hangs from a silk thread \(S,\) which makes an angle \(\theta\) with a large charged conducting sheet \(P,\) as shown in the figure. The surface charge density \(\sigma\) of the sheet is proportional to: 

1. \(\sin\theta\)
 2. \(\tan\theta\)
 3. \(\cos\theta\)
 4. \(\cot\theta\)

Two-point charges +8q and –2q are located at x = 0 and x = L respectively. The location of a point on the x-axis at which the net electric field due to these two point charges is zero is 

1. 8 L

2. 4 L

3. 2 L

4. $\frac{L}{4}$

Three infinitely long charge sheets are placed as shown in the figure. The electric field at point P is 

(1) $\frac{2\sigma }{{\epsilon }_o}\hat{k}$

(2) $-\frac{2\sigma }{{\epsilon }_o}\hat{k}$

(3) $\frac{4\sigma }{{\epsilon }_o}\hat{k}$

(4) $-\frac{4\sigma }{{\epsilon }_o}\hat{k}$

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.

A cylinder of radius R and length L is placed in a uniform electric field E parallel to the cylinder axis. The total flux for the surface of the cylinder is given by 

(1) $2\pi R^{2}E$

(2) $\pi R^2/E$

(3) $(\pi R^2-\pi R)/E$ 

(4) Zero

Electric field at a point varies as r⁰ for

(1) An electric dipole

(2) A point charge

(3) A plane infinite sheet of charge

(4) A line charge of infinite length