Electric Charges and Fields

These MCQs are based on the Electric Charges and Fields(The electric field is an alteration of space caused by the presence of an electric charge. It mediates the electric force between a source charge and a test charge).

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

10^-23 C 10^-37 C 10^-47 C 10^-20 C

Four charges equal to -Q are placed at the four corners of a square and a charge q is at its centre. If the system is in equilibrium the value of q is

-Q (1 + 2√2)/4 Q (1 + 2√2)/4 -Q (1 + 2√2)/2 Q (1 + 2√2)/2

Five charges q1, q2, q3, q4 and q are fixed at their positions as shown in figure S is a Gaussian surface. The Gauss’s law is given by ∮ E. ds= q/∈0 Which of the following statements is, correct?

E on the LHS of the above equation will have a contribution from q1, q5 and q3 while q on the RHS will have a contribution from q2 and q4 only. E on the LHS of the above equation will have a contribution from all charges while q on the RHS will have a contribution from q2 and q4 only. E on the LHS of the above equation will have a contribution from all charges while q on the RHS will have a contribution from q1, q3 and q5 only. Both E on the LHS and q on the RHS will have contributions from q2 and q4 only.

The electrostatic potential on the surface of a charged conducting sphere is 100 V. Two statements are made in this regard: S1: At any point inside the sphere, electric intensity is zero. S2: At any point inside the sphere, the electrostatic potential is 100 V. Which of the following is a correct statement?

S1 is true but S2 is false. Both S1 and S2 are false. S1 is true, S2 is also true and S1 is the cause of S2. S1 is true, S2 is also true but the statements are independent.

Which one of the following is the unit of electric field?

Coulomb Newton Volt N/C

If two conducting sphere are connected after charging separately then:

Electrostatic energy sphere energy will remain conserved Electrostatic energy charges remains conserved Electrostatic energy energy and charge remains conserved None

Three charges + 3q + q and Q are placed on a st. line with equal separation. In order to maket the net force on q to be zero, the value of Q will be :

+3q +2q -3q -4q

The number of electron-taken out from a body to produce 1 coulomb of charge will be :

6.25 × 10^18 625 × 10^18 6.023 × 10^23 None

The work done in rotating an electric dipole in an electric field:

W = ME (1 – cos θ) W = ME tan θ W = ME sec θ None

If an object is positively charged, theoretically the mass of the object ______

Increases slightly by a factor of 9.11*10-31 kg Decreases slightly by a factor of 9.11*10-31 kg Remains the same May increase or decrease

Why is gold used in the Gold-leaf electroscope?

Gold is easily available in nature Gold is malleable Gold is conducting in nature Gold is cheap

What happens to the plates of the apparatus if we measure alternating charge using a Gold-leaf oscilloscope?

It doesn’t diverge at all It diverges momentarily The plates give a proper divergence The degree of divergence increases and decreases repeatedly

Dr. Gilbert tried to hold a brass rod by hand and induce static electricity in it by friction. Why did he fail?

Static electricity is induced only on insulators while brass is conducting The induced static charge flew through his hand and body to the ground The static charge was not produced at all It is not possible to induce static electricity by friction

Gold-leaf electroscope can be used _______

Only to detect the presence of charge To detect the presence of charge as well as its nature (positive or negative) To measure the surface charge density To measure current

Consider a uniform electric field in the z direction. The potential is not a constant

In all space.

For any x for a given z.

For any y for a given z.

On the x-y plane for a given z.

When placed in a uniform field, a dipole experiences:

A net force

A torque

Both a net force and torque

Neither a net force nor a torque

If sphere of bad conductor is given charge then it is distributed on:

Surface