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An electric dipole is situated in an electric field of uniform intensity E whose dipole moment is p and moment of inertia is I. If the dipole is displaced slightly from the equilibrium position, then the angular frequency of its oscillations is 

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Explanation

When dipole is given a small angular displacement θ about it's equilibrium position, the restoring torque will be

τ=pEsinθ=pEθ   (as sinθ = θ)

or Id2θdt2=pEθ (as τ=Iα=Id2θdt2)

or d2θdt2=ω2θ with ω2=pEIω=pEI

An infinite number of electric charges each equal to 5 nano-coulomb (magnitude) are placed along x-axis at x = 1 cm, x = 2 cm, x = 4 cm, x = 8 cm ………. and so on. In the setup if the consecutive charges have opposite sign, then the electric field in Newton/Coulomb at x = 0 is 14πε0=9×109Nm2/c2

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Explanation

E=14πε0.5×109(1×102)25×109(2×102)2+5×109(4×102)2(5×109)(8×102)2+.....

 

E=9×109×5×10910411(2)2+1(4)21(8)2+...

 

E=45×1041+1(4)2+1(16)2+...45×1041(2)2+1(8)2+1(32)2+...

 

E=45×1041111645×104(2)21+142+1(16)2+...

 

E = 48 × 104 – 12 × 104 = 36 × 104 N/C  

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

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Suppose the charge of a proton and an electron differ slightly. One of them is -e and the other is e+e. If the net of electrostatic force and gravitaional force between two hydrogen atoms placed at a distance d (much greater than atomic size) apart is zero,then e is of the order [Given mass of hydrogen, mh=1.67×10-27 kg]

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Explanation

(c) Net charge on one H-atom 

=-e+e+e

Net electrostatic repulsive force between two H-atoms

Fe = Ke2d2

FG=Gm12d2

It is given that 

Fe-FG=0

    Ke2d2-Gm12d2=0

    e2=6.67×10-111.67×10-2729×109

       e=1.437×10-37C

 

An electric dipole is place at an angle of 30 with an electric field intensity 2×105 N/C. It experiences a torque equal to 4 Nm. The charge on the dipole, if the dipole length is 2 cm, is

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Explanation

 

(b) Torque on an electric dipole in an electric field,

             τ=p×Eτ=pE sin θ

where θ is the angle between E and p

 4=ρ×2×105×12p=4×10-5cmp=q2l q2l =4×10-5

Where 2l=2cm=2×10-2 m

q=4×10-52×10-2

2×10-3C=2mC

What is the flux through a cube of side a if a point charge of q is a one of its corner?

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Explanation

Charge enclosed=q/8

Therefore,flux ϕ=qenclosedε0

                    ϕ=q8ε0

Two parallel metal plates having charges +Q and -Q faces each other at a certain distance between them. If the plates are now dipped in kerosene oil tank, the electric field between the plates will

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Explanation

When the parallel metal plates are dipped in kerosene oil, the electric field between the plates decreases. This is because the kerosene oil has a higher permittivity than vacuum or air, which reduces the effective electric field according to the relation E = E₀/κ, where κ is the relative permittivity.

The mean free path of electrons in a metal is 4×10-8m.The electric field which can give on an average 2 eV energy to an electron in the metal will be in a unit of Vm-1 :

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Explanation

    Energy=2eV

     eV0=2 eV

 V0=2

Now, electric field E=24×10-8

                          =0.5×108

                         =5×107 Vm-1

Four particles each having charge q are placed at the vertices of a square of side a. The value of the electric potential at the midpoint of one of the side will be

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If W be the amount of heat produced in the process of charging an uncharged capacitor then the amount of energy stored in it is

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Explanation

Energy stored in capacitor = Heat produced in process of charging

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