Questions in electrostatics

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	If an insulated non-conducting sphere of radius R has charge density $\rho $. The electric field at a distance $r$from the centre of sphere $(r < R)$ will be
	Two plates are at potentials –10 V and +30 V. If the separation between the plates be 2 cm. The electric field between them is
	The electric potential inside a conducting sphere
	The wrong statement about electric lines of force is
	A charge produces an electric field of 1 N/C at a point distant 0.1 m from it. The magnitude of charge is
	A charged particle is suspended in equilibrium in a uniform vertical electric field of intensity 20000 V/m. If mass of the particle is $9.6 \times {10^{ - 16}}\,kg$, the charge on it and excess number of electrons on the particle are respectively $(g = 10\,m/{s^2})$
	The potential at a distance R/2 from the centre of a conducting sphere of radius R will be
	Four charges $+ Q,\, - Q,\, + Q,\, - Q$ are placed at the corners of a square taken in order. At the centre of the square
	The radius of nucleus of silver (atomic number = 47) is $3.4 \times {10^{ - 14}}m$. The electric potential on the surface of nucleus is $(e = 1.6 \times {10^{ - 19}}C)$
	Charges q, 2q, 3q and 4q are placed at the corners A, B, C and D of a square as shown in the following figure. The direction of electric field at the centre of the square is along