EASY
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An annular disc has inner and outer radius aand b. Surface density of charge is σ. The electric field at any point at a distance y along the axis of the disc is given by

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Important Questions on Interaction of Charged Particles, Electric Field and Potential

HARD

A thin disc of radius b=2a has a concentric hole of radius a in it (see figure). It carries uniform surface charge σ  on it. If the electric field on its axis at a height hh<<a from its centre is given as Ch then the value of C is

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MEDIUM
A simple pendulum of length L is placed between the plates of a parallel plate capacitor having electric field  E , as shown in figure. Its bob has mass m and charge  q . The time period of the pendulum is given by:
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HARD

Three charged particles AB and C with charges -4q,2q and -2q are present on the circumference of a circle of radius d. The charged particles A,C and centre O of the circle formed an equilateral triangle as shown in the figure. The electric field at the point O is
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EASY
Two charged thin infinite plane sheets of uniform charge density σ+ and σ-, where σ+>σ, intersect at the right angle. Which of the following best represents the electric field lines for the system:
HARD
The figures below depict two situations in which two infinitely long static line charges of constant positive line charge density λ are kept parallel to each other. In their resulting electric field, point charges q and -q are kept in equilibrium between them. The point charges are confined to move in the x direction only. If they are given a small displacement about their equilibrium positions, then the correct statements(s) is (are)

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MEDIUM
A particle of mass m and charge q is placed at rest in uniform electric field E and then released. The kinetic energy attained by the particle after moving a distance y is
HARD
A particle of mass m and charge q is released from rest in a uniform electric field. If there is no other force on the particle, the dependence of its speed v on the distance x travelled by it is correctly given by (graphs are schematic and not drawn to scale)
EASY
Two metal plates having a potential difference of 800 V are 2 cm apart. It is found that a particle of mass 1.96×10-15 kg remains suspended in the region between the plates. The charge on the particle must be (e= elementary charge)
MEDIUM
Two parallel infinite line charges with linear charge densities +λ C m-1 and -λ C m-1 are placed at a distance of 2R in free space. What is the electric field mid-way between the two-line charges?
EASY
The bob of a simple pendulum has mass 2 g and a charge of 5.0 μC. It is at rest in a uniform horizontal electric field of intensity 2000 V/m At equilibrium, the angle that the pendulum makes with the vertical is:
takeg=10 m/s2
MEDIUM
Suppose that intensity of a laser is 315π W m-2. The rms electric field, in units of V m-1 associated with this source is close to the nearest integer is -ε0=8.86×10-12 C2 N m-2; c=3×108 m s-1
HARD
A wire of length L=20 cm is bent into a semi-circular arc and the two equal halves of the arc are uniformly charged with charges +Q and -Q as shown in the figure. The magnitude of the charge on each half is Q=103ε0, where ε0 is the permittivity of free the space. The net electric field at the centre O is

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EASY
A spherical conductor of radius 10 cm has a charge of 3.2×107 C distributed uniformly. What is the magnitude of electric field at a point 15 cm from the centre of the sphere?
14πε0=9×109 Nm2 C-2
MEDIUM
The electric fields of two plane electromagnetic plane waves in vacuum are given by E1=E0cosωt-kx j^ and E2=E0cosωt-ky k^, at t=0, a particle of charge q is at origin with a velocity v=08c j^ ( c is the speed of light in vaccum). The instantaneous force experienced by the particle is:
HARD

A uniform electric field, E=-4003 j^ N C-1 is applied in a region. A charged particle of mass m carrying positive charge q is projected in this region with an initial speed of 210×106 m s-1. This particle is aimed to hit a target T, which is 5 m away from its entry point into the field as shown schematically in the figure. Take qm=1010 C kg-1. Then

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MEDIUM
A particle of mass 2×10-6 kg with a charge 5×10-6 C is hanging in air above a similarly charged conducting surface. The charge density of the surface is (Assume ϵ0=8.85×10-12 C2 N-1M-2 and g=10 m s-2)
EASY
An infinitely long thin straight wire has uniform charge density of 14×10-2 C m-1. What is the magnitude of electric field at a distance 20 cm from the axis of the wire?
HARD
Four point charges -q, +q, +q and -q are placed on y-axis at y=-2d, y=-d, and y=+2d, respectively. The magnitude of the electric field E at a point on the x-axis at x=D, with Dd, will behave as:
EASY
The electric field in a certain region is acting radially outward and is given by E=Ar. A charge contained in a sphere of radius a centred at the origin of the field will be given by
MEDIUM
Two point charges q110 μC and q2-25 μC are placed on the x -axis at x=1 m and x=4 m respectively. The electric field in V m-1 at a point y=3 m on y-axis is,

Take 14πϵ0=9×109 N m2C-2