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In the given diagram, there is a conducting sphere of radius r1 which is surrounded by a dielectric of relative permittivity εr. If conducting sphere is given charge q, then the surface density of polarization charges, on the outer surface of the dielectric layer, is
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Important Questions on Electrostatics

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There is a uniform spherically symmetric surface charge density at a distance R0 from the origin. The charge distribution is initially at rest and starts expanding because of mutual repulsion. The figure that represents best the speed VRt of the distribution as a function of its instantaneous radius Rt is:
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A uniformly charged solid sphere of radius R has potential V0 (measured with respect to ) on its surface. For this sphere the equipotential surfaces with potential 3V02,5V04,3V04 and V04 have radius R1 , R2, R3 and R4 respectively. Then

Note : This question had two option correct at the time of examination. Proper corrections are made in the question to avoid it.

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An electron is moving around an infinite linear charge in circular path of diameter 0.30m. If linear charge density is 106 Cm, then calculate the speed of an electron. mc=9.0×10-31kg, e=1.6×10-19C.
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Three point charges 4q, Q and q are placed in a straight line of length L at points 0,L2 and L respectively. The net force on charge q is zero. The value of Q is
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A non-uniformly charged sphere has charge density given by ρ=ar2R where a is a constant, r is the distance from the centre and R is the radius of the sphere. Then the total charge inside the sphere is proportional to
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A charge Q is uniformly distributed on the circumference of a circular ring of radius a. Find the intensity of the electric field at a point at a distance x from the centre of the axis of the ring.
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What is volume charge density? Write its SI unit. 
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Four point charges qA=2 μC, qB=-5 μC, qC=2 μC, qD=-5 μC are located at the corners of a square ABCD of side 10 cm. The force acting on a charge of 1 μC placed at centre of the square is

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Find out the surface charge density at the intersection of point x=3 m plane and x-axis, in the region of uniform line charge of 8 nC m-1 lying along the z-axis in free space.
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Sixty four conducting drops each of radius 0.02 m and each carrying a charge of 5 μC are combined to form a bigger drop. The ratio of surface density of bigger drop to the smaller drop will be
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Three concentric metal shells A, B and C of respective radii a, b and c (a < b < c) have surface charge densities  +σ, -σ  and +σ respectively. The potential of shell B  is:
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Shown in the figure is a shell made of a conductor. It has inner radius a and outer radius b, and carries charge Q . At its centre a dipole p is placed as shown then:
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Let E1r, E2r and E3r be the respective electric fields at a distance r from a point charge Q, an infinitely long wire with constant linear charge density λ , and an infinite plane with uniform surface charge density σ . If E1r0=E2r0=E3r0 at a given distance r0 , then
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Define surface charge density and volume charge density of an electric charge. Also, state its unit.
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Three charges are placed at the three vertices of an equilateral triangle of side a as shown in the figure. The force experienced by the charge placed at the vertex A in a direction normal to BC is

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Four equal charges of value +Q are placed at any four vertices of a regular hexagon of side a. By suitably choosing the vertices, what can be the maximum possible magnitude of electric field at the centre of the hexagon?
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Eleven equal point charges, all of them having a charge +Q, are placed at all the hour positions of a circular clock of radius r except at the 10 h position. What is the electric field strength at the centre of the clock?

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Charge is distributed within a sphere of radius R with a volume charge density ρr=Ar2e-2ra, where A and a are constants. If Q is the total charge of this charge distribution, the radius R is_____.
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Two infinite planes each with uniform surface charge density +σ are kept in such a way that the angle between them is 30o . The electric field in the region shown between them is given by:
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Let a total charge 2Q be distributed in a sphere of radius R, with the charge density given by ρ(r)=kr, where r is the distance from the centre. Two charges A and B , of -Q each, are placed on diametrically opposite points, at equal distance, a, from the centre. If A and B do not experience any force, then: