# NEET

Explore popular questions from Electrostatics for NEET. This collection covers Electrostatics previous year NEET questions hand picked by experienced teachers.

## Biology

Electrostatics

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Q 1. An electric dipole is placed in a uniform electric field. The dipole will experience

A

a force that will displace it in the direction of the field

B

a force that will displace it in a direction opposite to the field.

a torque which will rotate it without displacement

D

a torque which will rotate it and a force that will displace it

##### Explanation

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Q 2. If {tex} E _ { a } {/tex} be the electric field strength of a short dipole at a point on its axial line and {tex} E _ { \mathrm { c } } {/tex} that on the equatorial line at the same distance, then

A

{tex} E _ { e } = 2 E _ { q } {/tex}

{tex} E _ { a } = 2 E _ { e } {/tex}

C

{tex} E _ { a } = E _ { e } {/tex}

D

None of the above

##### Explanation

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Q 3. Three positive charges of equal value q are placed at vertices of an equilateral triangle. The resulting lines of force should be sketched as in

A

B

D

##### Explanation

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Q 4. Two charge {tex} q {/tex} and {tex} - 3 q {/tex} are placed fixed on {tex} x {/tex} -axis separated by distance {tex} d . {/tex} Where should a third charge 2{tex} q {/tex} be placed such that it will not experience any force?

A

{tex} \frac { d - \sqrt { 3 } d } { 2 } {/tex}

{tex} \frac { d + \sqrt { 3 } d } { 2 } {/tex}

C

{tex} \frac { d + 3 d } { 2 } {/tex}

D

{tex} \frac { d - 3 d } { 2 } {/tex}

##### Explanation

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Q 5. If n drops, each charged to a potential {tex} \mathrm {V} {/tex}, coalesce to form a single drop. The potential of the big drop will be

A

{tex} \frac { \mathrm V } { \mathrm n ^ { 2 / 3 } } {/tex}

B

{tex} \frac { \mathrm { V } } { \mathrm { n } ^ { 1 / 3 } } {/tex}

C

{tex} \mathrm { Vn } ^ { 1 / 3 } {/tex}

{tex} \mathrm { Vn } ^ { 2 / 3 } {/tex}

##### Explanation

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Q 6. The capacitance of a parallel plate capacitor is C{tex}_a{/tex} (Fig. a). A dielectric of dielectric constant K is inserted as shown in fig. (b) and (c). If C{tex}_b{/tex} and C{tex}_c{/tex} denote the capacitance in fig. (b) and (c), then

both {tex} \mathrm { C } _ { \mathrm { b } } , \mathrm { C } _ { \mathrm { c } } > \mathrm { C } _ { \mathrm { a } } {/tex}

B

{tex} \mathrm { C } _ { \mathrm { c } } > \mathrm { C } _ { \mathrm { a } } {/tex} while {tex} \mathrm { C } _ { \mathrm { b } } > \mathrm { C } _ { \mathrm { a } } {/tex}

C

{tex} \operatorname { both } \mathrm { C } _ { \mathrm { b } } , \mathrm { C } _ { \mathrm { c } } < \mathrm { C } _ { \mathrm { a } } {/tex}

D

{tex} C _ { a } = C _ { b } = C _ { c } {/tex}

##### Explanation

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Q 7. What is the effective capacitance between X and Y ?

A

{tex}24 \mu F {/tex}

B

{tex}18 \mu F {/tex}

C

{tex}12 \mu F {/tex}

{tex}6 \mu F {/tex}

##### Explanation

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Q 8. There exists a non-uniform electric field along {tex} \mathrm { x } {/tex} -axis as shown in the figure below. The field increases at a uniform rate along {tex} + \mathrm { ve } {/tex} x-axis. A dipole is placed inside the field as shown. Which one of the following is correct for the dipole?

A

Dipole moves along positive {tex} x {/tex} -axis and undergoes a clockwise rotation

B

Dipole moves along negative {tex} \mathrm { x } {/tex} -axis and undergoes a clockwise rotation

C

Dipole moves along positive {tex} \mathrm { x } {/tex} -axis and undergoes a anticlockwise rotation

Dipole moves along negative {tex} x {/tex} -axis and undergoes a anticlockwise rotation

##### Explanation

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Q 9. Four metallic plates each with a surface area of one side A, are placed at a distance d from each other. The two outer plates are connected to one point A and the two other inner plates to another point B as shown in the figure. Then the capacitance of the system is

A

{tex} \frac { \varepsilon _ { 0 } \mathrm { A } } { \mathrm { d } } {/tex}

{tex} \frac { 2 \varepsilon _ { 0 } \mathrm { A } } { \mathrm { d } } {/tex}

C

{tex} \frac { 3 \varepsilon _ { 0 } \mathrm { A } } { \mathrm { d } } {/tex}

D

{tex} \frac { 4 \varepsilon _ { 0 } \mathrm { A } } { \mathrm { d } } {/tex}

##### Explanation

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Q 10. If a slab of insulating material {tex} 4 \times 10 ^ { - 5 } \mathrm { m } {/tex} thick is introduced between the plates of a parallel plate capacitor, the distance between the plates has to be increased by {tex} 3.5 \times 10 ^ { - 5 } \mathrm { m } {/tex} to restore the capacity to original value. Then the dielectric constant of the material of slab is

8

B

6

C

12

D

10

##### Explanation

If K is the dielectric constant, t is thickness and the distance increased is x then, {tex} x = t {/tex} {tex} ( 1 - \frac {1}{K} ) {/tex} 3.5 x 10-5 = {tex} t( 1 - \frac {1}{K} ) {/tex} {tex} ( 1 - \frac {1}{K} ) {/tex} = {tex}( \frac { \mathrm {3.5 x 10 ^ {-5}}}{\mathrm {4 x 10 ^ {-5}}}) {/tex} {tex} ( 1 - \frac {1}{K} ) {/tex} = 0.875 {tex} \frac {1}{K} {/tex} = 1 - 0.875 = 0.125 K = 8

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Q 11. A unit charge moves on an equipotential surface from a point {tex} \mathrm { A } {/tex} to point {tex} \mathrm { B } {/tex} , then

A

{tex} \mathrm { V } _ { \mathrm { A } } - \mathrm { V } _ { \mathrm { B } } = + \mathrm { ve } {/tex}

{tex} V _ { A } - V _ { B } = 0 {/tex}

C

{tex} \mathrm { V } _ { \mathrm { A } } - \mathrm { V } _ { \mathrm { B } } = - \mathrm { ve } {/tex}

D

it is stationary

##### Explanation

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Q 12. If the electric flux entering and leaving a closed surface are {tex} 6 \times 10 ^ { 6 } {/tex} and {tex} 9 \times 10 ^ { 6 } {/tex} S.I. units respectively, then the charge inside the surface of permittivity of free space {tex} \varepsilon _ { 0 } {/tex} is

A

{tex} \varepsilon _ { 0 } \times 10 ^ { 6 } {/tex}

B

{tex} - \varepsilon _ { 0 } \times 10 ^ { 6 } {/tex}

C

{tex} - 2 \varepsilon _ { 0 } \times 10 ^ { 6 } {/tex}

{tex} 3 \varepsilon _ { 0 } \times 10 ^ { 6 } {/tex}

##### Explanation

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Q 13. Identify the false statement.

A

Inside a charged or neutral conductor, electrostatic field is zero

The electrostatic field at the surface of the charged conductor must be tangential to the surface at any point

C

There is no net charge at any point inside the conductor

D

Electrostatic potential is constant through out the volume of the conductor

##### Explanation

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Q 14. An uniform electric field {tex} \mathrm { E } {/tex} exists along positive {tex} \mathrm { x } {/tex} -axis. The work done in moving a charge 0.5{tex} \mathrm { C } {/tex} through a distance 2{tex} \mathrm { m } {/tex} along a direction making an angle {tex} 60 ^ { \circ } {/tex} with {tex} \mathrm { x } {/tex} -axis is 10{tex} \mathrm { J } {/tex} . Then the magnitude of electric field is

A

5{tex} \mathrm { Vm } ^ { - 1 } {/tex}

B

2{tex} \mathrm { Vm } ^ { - 1 } {/tex}

C

{tex} \sqrt { 5 } \mathrm { Vm } ^ { - 1 } {/tex}

{tex}20 \mathrm { Vm } ^ { - 1 } {/tex}

##### Explanation

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Q 15. A hollow cylinder has a charge {tex} q {/tex} coulomb within it. If {tex} \phi {/tex} is the electric flux in units of voltmeter associated with the curved surface {tex} B {/tex} , the flux linked with the plane surface {tex} A {/tex} in units of voltmeter will be

A

{tex} \frac { q } { 2 \varepsilon _ { 0 } } {/tex}

B

{tex} \frac { \phi } { 3 } {/tex}

C

{tex} \frac { q } { \varepsilon _ { 0 } } - \phi {/tex}

{tex} \frac { 1 } { 2 } \left( \frac { q } { \varepsilon _ { 0 } } - \phi \right) {/tex}

##### Explanation

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Q 16. Three point charges {tex} Q _ { 1 } , Q _ { 2 } , Q _ { 3 } {/tex} in the order are placed equally spaced along a straight line. {tex} Q _ { 2 } {/tex} and {tex} Q _ { 3 } {/tex} are equal in magnitude but opposite in sign. If the net force on {tex} Q _ { 3 } {/tex} is zero. The value of {tex} Q _ { 1 } {/tex} is

{tex} Q _ { 1 } = 4 \left( Q _ { 3 } \right) {/tex}

B

{tex} Q = 2 \left( Q _ { 3 } \right) {/tex}

C

{tex} \mathrm { Q } _ { 1 } = \sqrt { 2 } \left( \mathrm { Q } _ { 3 } \right) {/tex}

D

{tex} Q _ { 1 } = \left| Q _ { 3 } \right| {/tex}

##### Explanation

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Q 17. Electric charge is uniformly distributed along a long straight wire of radius 1{tex} \mathrm { mm } {/tex} . The charge per {tex} \mathrm { cm } {/tex} length of the wire is Q coulomb. Another cylindrical surface of radius 50{tex} \mathrm { cm } {/tex} and {tex} \mathrm { d } {/tex} length 1{tex} \mathrm { m } {/tex} symmetrically encloses the wire. The total electric flux passing through the cylindrical surface is

A

{tex} \frac { Q } { \varepsilon _ { 0 } } {/tex}

{tex} \frac { 100Q } { \varepsilon _ { 0 } } {/tex}

C

{tex} \frac { 10 Q } { \pi \varepsilon _ { 0 } } {/tex}

D

{tex} \frac { 100Q } { \pi \varepsilon _ { 0 } } {/tex}

##### Explanation

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Q 18. A small sphere carrying a charge 'q' is hanging in between two parallel plates by a string of length L. Time period of the pendulum is T o. When parallel plates are charged, the time period changes to T. The ratio T/T0 is equal to

A

{tex} \left( \frac { g + \frac { q E } { m } } { g } \right) ^ { 1 / 2 } {/tex}

B

{tex} \left( \frac { g } { g + \frac { q E } { m } } \right) ^ { 3 / 2 } {/tex}

{tex} \left( \frac { g } { g + \frac { q E } { m } } \right) ^ { 1 / 2 } {/tex}

D

{tex} \left( \frac { g } { g + \frac { q E } { m } } \right) ^ { 5 / 2 } {/tex}

##### Explanation

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Q 19. An electric dipole, consisting of two opposite charges of {tex} 2 \times 10 ^ { - 6 } \mathrm { C } {/tex} each separated by a distance 3{tex} \mathrm { cm } {/tex} is placed in an electric field of {tex} 2 \times 10 ^ { 5 } \mathrm { N } / \mathrm { C } {/tex} . Torque acting on the dipole is

A

{tex} 12 \times 10 ^ { - 1 } N m {/tex}

B

{tex} 12 \times 10 ^ { - 2 } N m {/tex}

{tex} 12 \times 10 ^ { - 3 } N m {/tex}

D

{tex} 12 \times 10 ^ { - 4 } N m {/tex}

##### Explanation

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Q 20. The electric field in a certain region is acting radially outward and is given by {tex} \mathrm { E } = \mathrm { Ar } {/tex} . A charge contained in a sphere of radius 'a' centred at the origin of the field, will be given by

A

{tex} A \varepsilon _ { 0 } a ^ { 2 } {/tex}

4{tex} \pi \varepsilon _ { 0 } \mathrm { Aa } ^ { 3 } {/tex}

C

{tex} \varepsilon _ { 0 } \mathrm { Aa } ^ { 3 } {/tex}

D

4{tex} \pi \varepsilon _ { 0 } \mathrm { Aa } ^ { 2 } {/tex}

##### Explanation

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Q 21. The spatial distribution of electric field due to charges {tex} ( \mathrm { A } , \mathrm { B } ) {/tex} is shown in figure. Which one of the following statements is correct?

{tex} A {/tex} is {tex} + v e {/tex} and {tex} B - v e , | A | > | B |{/tex}

B

{tex} A {/tex} is {tex} - v e {/tex} and {tex} B + v e , | A | = | B | {/tex}

C

Both are + ve but {tex} A > B {/tex}

D

Both are - ve but {tex} \mathrm { A } > \mathrm { B } {/tex}

##### Explanation

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Q 22. For distance far away from centre of dipole the change in magnitude of electric field with change in distance from the centre of dipole is

A

zero

B

same in equatorial plane as well as axis of dipole.

C

more in case of equatorial plane of dipole as compared to axis of dipole.

more in case of axis of dipole as compared to equatorial plane of dipole.

##### Explanation

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Q 23. A charge {tex} Q {/tex} is placed at each of the opposite corners of a square. A charge {tex} q {/tex} is placed at each of the other two corners. If the net electrical force on {tex} Q {/tex} is zero, then {tex} Q / q {/tex} equals:

A

{tex} - 1 {/tex}

B

{tex} 1 {/tex}

C

{tex} - \frac { 1 } { \sqrt { 2 } } {/tex}

{tex} - 2 \sqrt { 2 } {/tex}

##### Explanation

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Q 24. Which of the following statements is incorrect?

A

The charge {tex} q {/tex} on a body is always given by {tex} q = \mathrm { n } e {/tex} where {tex} n {/tex} is any integer, positive or negative.

B

By convention, the charge on an electron is taken to be negative.

C

The fact that electric charge is always an integral multiple of {tex} \mathrm { e } {/tex} is termed as quantisation of charge.

The quatisation of charge was experimentally demonstrated by Newton in 1912 .

##### Explanation

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Q 25. Two positive ions, each carrying a charge {tex} q , {/tex} are separated by a distance {tex} d . {/tex} If {tex} F {/tex} is the force of repulsion between the ions, the number of electrons missing from each ion will be (e being the charge of an electron)

A

{tex} \frac { 4 \pi \varepsilon _ { 0 } F d ^ { 2 } } { e ^ { 2 } } {/tex}

B

{tex} \sqrt { \frac { 4 \pi \varepsilon _ { 0 } F e ^ { 2 } } { d ^ { 2 } } } {/tex}

{tex} \sqrt { \frac { 4 \pi \varepsilon _ { 0 } F d ^ { 2 } } { e ^ { 2 } } } {/tex}

D

{tex} \frac { 4 \pi \varepsilon _ { 0 } F d ^ { 2 } } { q ^ { 2 } } {/tex}