Question Pool ELECTRIC CHARGES AND FIELD

# ELECTRIC CHARGES AND FIELD - SAMAGRA Question Pool & Answers | Class 12

Kerala Syllabus SAMAGRA SCERT SAMAGRA Question Pool for Class 12 Physics ELECTRIC CHARGES AND FIELD Qn 1.

Explain Quantization of charge

Quantization of charge means the total charge in a body is always an integral multiple of a fundamental charge 'e' , which is equal to the charge of an

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Qn 2.

What does an electric dipole experience when kept with an angle in a uniform electric field and non−uniform electric field?

Electric dipole experience torque in a uniform electric field and net force and torque in non−uniform electric

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Qn 3.

A hollow metal ball carrying an electric charge produces no electric

field at points

(a) outside the sphere

(b) on its surface

(c) inside the sphere

(d) at a distance more than twice

(c) inside the sphere

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Qn 4.

In a region of uniform electric field E, a hemispherical body is placed in such a way that the field is parallel to its base(as shown in the figure).What is the total flux linked with the curved surface? zero.

The flux linked with the body is zero as it does not enclose any

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Qn 5.

An electric dipole is placed in a uniform electric field of intensity E. Let θ be the angle between dipole moment and electric field.

(a)Derive an expression for the torque acting on the electric dipole in vector form. (2)

(b)What orientation of the dipole corresponds to stable and unstable equilibrium? (1)

(c)Write the equation of potential energy corresponds to stable equilibrium (1)

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Qn 6.

(a)Name the theorem used to find the electric flux through a surface enclosing charge.

(b) Using the theorem,derive an expression for the electric field due to an infinite plane sheet with surface charge density σ

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Qn 7.

An oil drop of charge of 2 electrons fall freely with a terminal speed. Determine the mass of oil drop so, it can move upward with same terminal speed, if electric field of 2x103 V/m.

Hint: Since the drop falls freely with terminal (uniform)

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Qn 8.

Calculate the work done in carrying a charge q once round over a closed circular path of radius 'r' and a charge Q is at the centre.

Hint: The electrostatic force is conservative in nature. In a conservative force field, the total work done in a round trip is always zero.

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Qn 9.

An electric dipole made of positive and negative charges, each of 1μC and placed at a distance 2 cm apart. If the dipole is placed in an electric field of 105 N/C, what is the maximum torque the field can exert on the dipole, if it is turned from a position θ=0˚ to θ=180˚?

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Qn 10.

What is the electric field intensity at point at a distance 20 cm on a line making an angle 45˚ with the axis of the electric dipole of dipole moment 10 Cm?

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Qn 11.

An electric dipole with dipole moment 4x10-9 C m is aligned at 30° with the direction of a uniform electric field of magnitude 5x104N/C. Find the value of torque acting on the dipole.

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Qn 12.

A polythene piece rubbed with wool is found to have a negative charge of -3x10-7 C.

a. Estimate the number of electrons transferred (from which to which?)

b. Is there a transfer of mass from wool to polythene?

Answer: When polythene is rubbed with wool, number of electrons get transferred from wool to polythene. Hence wool becomes negatively

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Qn 13.

A pendulum bob of mass m and charge q is suspended by a thread of length l. The pendulum is placed in a region of a uniform electric field E directed vertically upward. If the electrostatic force acting on the sphere is less than that of gravitational force, what is the time period T with which the pendulum oscillates in the field?

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Qn 14.

An electron is projected with velocity 107 m/s at an angle θ(=30˚) with the horizontal in a region of uniform electric field of 5000 N/C vertically upwards. Find the maximum distance covered by the electron in vertical direction above its initial level.

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Qn 15.

a. “ Electric charge of a body is quantised”. Explain the statement.

b. Why can one ignore quantisation of electric charge when dealing with macroscopic or large scale charges?

Answer: Charge of an object is always quantised. It means that only integral number of electrons can be transferred from one body to the

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Qn 16.

The electrostatic force on a small sphere of charge 0.4 μC due to another small sphere of charge 0.8 μC in air is 0.2N. (a)What is the distance between the spheres (b)What is the force on the second sphere due to the first?

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Qn 17.

The idea of electric field lines is useful in pictorially mapping the electric field around charges.

a. Give any two properties of electric lines of force.

b. State Gauss's theorem in electrostatics.

c. Using the theorem, derive an expression for the electric field due to a uniformly charged spherical shell.

i. At a point outside the shell.

ii. At a point inside the shell.

d. A point charge of +10μC is at a distance of 5 cm directly above the centre of a square of side 10 cm as shown in the figure. What is the electric flux through the square? Get Free Study Materials + 1 Week Free Trial of BrainsPrep Class 12 Tuition

Qn 18.

March 2012:

Name the physical quantity which has its unit Joule/Coulomb. Is it a vector or a scalar?

b. Two plane sheets of charge densities +σ and -σ are kept in air as shown in figure. What are the electric field intensities at points A and B? Get Free Study Materials + 1 Week Free Trial of BrainsPrep Class 12 Tuition

Qn 19.

Write the expression for the electric field due to a uniformly charged plane sheet. How this electric field differ from field due to a point charge ?

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Qn 20.

Gauss's law can be used to determine the electric field due to a charge distribution.

a. Below are some statements about Gauss's law. State true or false.

i. Gauss's law is valid only for symmetrical charge distributions.

ii. The electric field calculated by Gauss's law is the field due to charges inside the Gaussian surface.

b. Apply Gauss's law to find the electric field due to an infinitely long plane sheet of charge.

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Qn 21.

The region around a charge where its effect can be felt is called the electric field.

a. The electric field lines corresponding to an electric field is shown below. The figure suggests that

i. EA>EB>EC                                                     ii. EA <EB<EC                                     iii. EA =EB = EC

iv. EA =Ec >EB                                                    v. EA =Ec <EB HInt: The relative density of

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Qn 22.

a. Gauss's law is true for any closed surface, no matter what its shape or size. Say the following statements are true or false.

i. Gauss's law implies that the total electric flux through a closed surface is zero if no charge is enclosed by the surface.

ii. This law is useful for the calculation of electrostatic field when the system don't possess any symmetry.

b. In a uniform electric field, we know that the dipole experiences no net force , but experiences a torque having a relation with p and E given by ....................... where the parameters p and E are having their usual meaning.

a.

i. True

ii. False

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Qn 23.

a. All free charges are integral multiples of basic unit of charge e. The quantisation rule of electric charge implies

(a) Q=e                             (b)Q=1/e

(c)Q= ne                            (d)Q=e2

b. Match the following quantities in column A with their units in column B

 A B i. Force a. Coulomb (C) ii. Charge b. N/C or V/m iii. Electric field d. Coulomb meter (Cm) iv. Dipole moment e. Newton (N)

c. Electric field is an important way of characterising the electrical environment of a system of charges.

Two point charges q1 and q2 of magnitude +10-8 C and – 10-8 C respectively are placed 0.1 m apart. Calculate the fields at points A, B and C as shown in figure Get Free Study Materials + 1 Week Free Trial of BrainsPrep Class 12 Tuition

Qn 24.

(a) The ratio of electric field on the equatorial point and at the axial point at equal distances from the centre of a short electric dipole is

(b) A closed surface encloses an electric dipole. What is the electric flux through the surface?

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Qn 25.

The value of electric field inside a charged conductor is ....................

Zero

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Qn 26.

What should be the flux linked with one face of a cube, if a point charge q is placed at one corner of a cube?

(a)q/ε0                              (b)q/2ε0                                  (c)q/3ε0                              (d)q/8ε0

Hint: The flux linked with each face will be one-eighth

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Qn 27.

A point charge Q is placed at the centre of a hemisphere. The ratio of electric flux passing through curved surface and plane surface of the hemisphere is :

(a)1:1                                            (b)1:2

(c)2π:1                                         (d)4π:1

Hint: Net electric flux =Q/ε0= half flux through curved

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Qn 28.

A surface S=10 is kept in an electric field . How much electric flux will come out through the surface?

(a)40 unit

(b)50 unit

(c)30 unit

(d)20 unit

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Qn 29.

Flux coming out from a unit positive charge placed in air is

(a)ε0

(b)ε0-1

(c)(4πε0)-1

(d)4πε0)

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Qn 30.

Two point charges +4e and +e are kept at a distance x apart. At what distance charge q must be placed from a charge +e so that q is in equilibrium?

(a)x/2                                        (b)2x/3

(c)x/3                                        (d)x/3

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Qn 31.

Force acting upon a charged particle, kept between the charged pair of plates is F. If one of the plates is removed, force acting on the same particle will become :

(a)3F

(b)F/2

(c)F

(d)2F

(b) F/2

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Qn 32.

The intensity of electric field due to a proton at a distance of 0.2 nm is

(a)3.6x108 N/C

(b)3.6x1010 N/C

(c)3.6x1012N/C

(d)3.6x1013N/C

(b)3.6x1010 N/C

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Qn 33.

A positively charged ball hangs from a silk thread. We put a positive test charge qo at a point and measure , then it can be predicted that the electric field strength E becomes:

(a)Greater than (b) Equal to (c) Less than (d)Cannot be estimated

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Qn 34.

A body can be negatively charged by

(a)giving excess of electrons to it.

(b)removing from electrons from it.

(c)giving some protons to it.

(d)removing some neutrons from it

(a)giving excess of electrons to it

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Qn 35.

There are two charges +1μC and +5μC. The ratio of the forces acting on them will be

(a)1:5 (b)1:1 (c)5:1 (d)1:25

(b)1:1

Hint: Electrostatic force of attraction or repulsion obeys Newton's 3rd law. Hence force experienced on both the charges is the

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Qn 36.

An isolated solid metallic sphere is given +Q charge. The charge will be distributed on the sphere:

(a)Uniformly, but only on the surface

(b)Only on surface but non uniformly

(c) uniformly inside the volume.

(d) Non-uniformly inside the volume

(a)Uniformly, but only on the surface

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Qn 37.

(4). Electric charge in uniform motion produces

(a) An electric field only

(b) A magnetic field only

(c) Both (a) and (b)

(d) Neither electric nor magnetic field

(c) Both (a) and (b)

Accelerated electric charges produces electromagnetic

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Qn 38.

If a glass rod is rubbed with silk, it acquires a positive charge because:

(a) Protons are added to it

(b)Protons are removed from it

(c) Electrons are added to it

(d)Electrons are removed from it

(d): Electrons are removed from it.

A body aquires positive charge when it loses

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Qn 39.

A billion electrons are added to a body, its charge becomes:

(a) 1.6x10-19C (b) 1.6x10-28C

(c)-1.6x10-10C (d)-1.6x10-28C

(c) -1.6x10-10C

charge: -1.6x10-19

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Qn 40.

In comparison with the electrostatic between two electrons, the electrostatic force between two protons is

(a)Greater (b)Same

(c) Smaller (d) Zero

Hint: Electrostatic force is independent of the mass of objects. Electron and proton are having different masses but their charges have