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Home > NCERT Solutions > Punjab School Education Board > Class 12 > Physics > Physics Part I > Chapter 1 Electric Charges And Fields

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TextBook Solutions for Punjab School Education Board Class 12 Physics Physics Part I Chapter 1 Electric Charges And Fields

Question 1

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What is the force between two small charged spheres having charges of 2 x 10^–7 C and 3 x 10^–7C placed 30 cm apart in air?

Solution

Given,
$C harge, q_{1} = 2 \times 10^{- 7} C, C harge, q_{2} = 3 \times 10^{- 7} C r = 30 cm = 0.3 m$

where, r is the distance between two charges.

Using the formula,

$∴$ $F = \frac{1}{4 {πε}_{0}} \frac{q_{1} q_{2}}{r^{2}}$

$= \frac{9 \times 10^{9} \times 2 \times 10^{- 7} \times 3 \times 10^{- 7}}{(0.3)^{2}} = 6 \times 10^{- 3} N (Repulsive)$

Repulsive in nature since both charges are positive.

Question 2

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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 0.2 N.
(a) What is the distance between the two spheres?
(b) What is the force on the second sphere due to the first?

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Question 3

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Check that the ratio $\frac{{ke}^{2}}{{Gm}_{e} m_{p}}$ is dimensionless. Look up a table of physical constants and determine the value of this ratio. What does the ratio signify?

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Question 4

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a) Explain the meaning of the statement 'electric charge of a body is quantised'.
b) why can one ignore quantisation of electric charge when dealing with macroscopic i.e., large scale charges?

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Question 5

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When a glass rod is rubbed with a silk cloth, charges appear on both. A similar phenomenon is observed with many other pairs of bodies. Explain how this observation is consistent with the law of conservation of charge.

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Question 6

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Four point charges q_A = 2 μC, q_B = – 5 μC, q_c = 2 μC, and q_D = –5 μC are located at the corners of a square ABCD of side 10 cm. What is the force on a charge of 1 μC placed at the centre of the square?

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Question 7

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a) An electrostatic field line is a continuous curve. That is, a field line cannot have sudden breaks. Why not?
b) Explain why two field lines never cross each other at any point?

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Question 8

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Two point charges q_A = 3 μC and q_B = –3 μC are located 20 cm apart in vacuum.
(a) What is the electric field at the midpoint O of the line AB joining the two charges?
(b) If a negative test charge of magnitude 1.5 x 10^–9 C is placed at this point, what is the force experienced by the test charge?

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Question 9

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A system has two charges q_A = 2.5 x 10^–7 C and q_B = –2.5 x 10^–7 C located at points A: (0, 0, –15 cm) and B: (0, 0, + 15 cm), respectively. What are the total charge and electric dipole moment of the system?

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Question 10

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An electric dipole with dipole moment 4 x 10^–9 C m is aligned at 30° with the direction of a uniform electric field of magnitude 5 x 10⁴ NC–¹. Calculate the magnitude of the torque acting on the dipole.

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TextBook Solutions for Punjab School Education Board Class 12 Physics Physics Part I Chapter 1 Electric Charges And Fields

What is the force between two small charged spheres having charges of 2 x 10^–7 C and 3 x 10^–7C placed 30 cm apart in air?

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 0.2 N.
(a) What is the distance between the two spheres?
(b) What is the force on the second sphere due to the first?

Check that the ratio $\frac{{ke}^{2}}{{Gm}_{e} m_{p}}$ is dimensionless. Look up a table of physical constants and determine the value of this ratio. What does the ratio signify?

a) Explain the meaning of the statement 'electric charge of a body is quantised'.
b) why can one ignore quantisation of electric charge when dealing with macroscopic i.e., large scale charges?

When a glass rod is rubbed with a silk cloth, charges appear on both. A similar phenomenon is observed with many other pairs of bodies. Explain how this observation is consistent with the law of conservation of charge.

Four point charges q_A = 2 μC, q_B = – 5 μC, q_c = 2 μC, and q_D = –5 μC are located at the corners of a square ABCD of side 10 cm. What is the force on a charge of 1 μC placed at the centre of the square?

a) An electrostatic field line is a continuous curve. That is, a field line cannot have sudden breaks. Why not?
b) Explain why two field lines never cross each other at any point?

A system has two charges q_A = 2.5 x 10^–7 C and q_B = –2.5 x 10^–7 C located at points A: (0, 0, –15 cm) and B: (0, 0, + 15 cm), respectively. What are the total charge and electric dipole moment of the system?

An electric dipole with dipole moment 4 x 10^–9 C m is aligned at 30° with the direction of a uniform electric field of magnitude 5 x 10⁴ NC–¹. Calculate the magnitude of the torque acting on the dipole.

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation

For Daily Free Study Material Join wiredfaculty

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TextBook Solutions for Punjab School Education Board Class 12 Physics Physics Part I Chapter 1 Electric Charges And Fields

What is the force between two small charged spheres having charges of 2 x 10–7 C and 3 x 10–7C placed 30 cm apart in air?

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 0.2 N.(a) What is the distance between the two spheres?(b) What is the force on the second sphere due to the first?

Check that the ratio ke2Gmempis dimensionless. Look up a table of physical constants and determine the value of this ratio. What does the ratio signify?

a) Explain the meaning of the statement 'electric charge of a body is quantised'.b) why can one ignore quantisation of electric charge when dealing with macroscopic i.e., large scale charges?

When a glass rod is rubbed with a silk cloth, charges appear on both. A similar phenomenon is observed with many other pairs of bodies. Explain how this observation is consistent with the law of conservation of charge.

Four point charges qA = 2 μC, qB = – 5 μC, qc = 2 μC, and qD = –5 μC are located at the corners of a square ABCD of side 10 cm. What is the force on a charge of 1 μC placed at the centre of the square?

a) An electrostatic field line is a continuous curve. That is, a field line cannot have sudden breaks. Why not?b) Explain why two field lines never cross each other at any point?

A system has two charges qA = 2.5 x 10–7 C and qB = –2.5 x 10–7 C located at points A: (0, 0, –15 cm) and B: (0, 0, + 15 cm), respectively. What are the total charge and electric dipole moment of the system?

An electric dipole with dipole moment 4 x 10–9 C m is aligned at 30° with the direction of a uniform electric field of magnitude 5 x 104 NC–1. Calculate the magnitude of the torque acting on the dipole.

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation

What is the force between two small charged spheres having charges of 2 x 10^–7 C and 3 x 10^–7C placed 30 cm apart in air?

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 0.2 N.
(a) What is the distance between the two spheres?
(b) What is the force on the second sphere due to the first?

Check that the ratio $\frac{{ke}^{2}}{{Gm}_{e} m_{p}}$ is dimensionless. Look up a table of physical constants and determine the value of this ratio. What does the ratio signify?

a) Explain the meaning of the statement 'electric charge of a body is quantised'.
b) why can one ignore quantisation of electric charge when dealing with macroscopic i.e., large scale charges?

Four point charges q_A = 2 μC, q_B = – 5 μC, q_c = 2 μC, and q_D = –5 μC are located at the corners of a square ABCD of side 10 cm. What is the force on a charge of 1 μC placed at the centre of the square?

a) An electrostatic field line is a continuous curve. That is, a field line cannot have sudden breaks. Why not?
b) Explain why two field lines never cross each other at any point?

A system has two charges q_A = 2.5 x 10^–7 C and q_B = –2.5 x 10^–7 C located at points A: (0, 0, –15 cm) and B: (0, 0, + 15 cm), respectively. What are the total charge and electric dipole moment of the system?

An electric dipole with dipole moment 4 x 10^–9 C m is aligned at 30° with the direction of a uniform electric field of magnitude 5 x 10⁴ NC–¹. Calculate the magnitude of the torque acting on the dipole.