An electric dipole is placed in uniform external electric field E → . Show that the torque on the dipole is given by τ → = p → × E → where p → is the dipole moment of the dipole. What is the net force experienced by the dipole? Identify two pairs of perpendicular vectors in the expression.

Consider an electric dipole consisting of charges + q and - q and of length 2 a placed in a uniform electric field E → making an angle θ with it. Magnitude of dipole moment, p = q × 2 a Force exerted on charge + q by field is F 1 → = q E → , along E → Force exerted on charged on charge - q by field F 2 → = − q E → opposite to E → F → Total = − q E → − q E → = 0 Hence the net translating force on a dipole in a uniform electric field is zero. But the two equal and opposite forces act at different points of the dipole. They form a couple which exerts a torque. τ → = 2 a → × F 1 → = 2 q ( a → × E → ) τ → = p → × E →

Obtain the expression for the torque τ → experienced by an electric dipole of dipole moment p in a uniform electric field E → .

Consider an electric dipole consisting of charges + q and - q and of length 2 a placed in a uniform electric field E → making an angle θ with it. Magnitude of dipole moment, p = q × 2 a Force exerted on charge + q by field is F 1 → = q E → , along E → Force exerted on charged on charge - q by field F 2 → = − q E → opposite to E → F → Total = − q E → − q E → = 0 Hence the net translating force on a dipole in a uniform electric field is zero. But the two equal and opposite forces act at different points of the dipole. They form a couple which exerts a torque. τ → = 2 a → × F 1 → = 2 q ( a → × E → ) τ → = p → × E →

In the expression for the torque τ → experienced by an electric dipole of dipole moment p in a uniform electric field E → . What would happen if the external field E → is increasing parallel to p → and anti-parallel to p → ?

In a non-uniform electric field, the + q and - q charges of dipole experience difference forces. As the field is increasing along the dipole, force on positive charge is slightly greater than that on the negative charge. Heave it tend to move along the electric field. Torque on the dipole depends on the direction of field at the locations of the dipole charges. When the electric field is increasing antiparallel to the dipole, force acting on the negative charge will be greater than that acting on the positive charge. Hence it tends move opposite to the electric field.

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What do you understand by an electric dipole? Derive an expression for the torque acting on an electric dipole, when held in a uniform electric field. Hence, define the dipole moment.

Important Questions on Electric Charges and Field

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12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 1 - Electric Charges and Field>Text Based Exercises>Q 22

An electric dipole is placed in uniform external electric field

\vec{E}

. Show that the torque on the dipole is given by

\vec{τ} = \vec{p} \times \vec{E}

where

\vec{p}

is the dipole moment of the dipole. What is the net force experienced by the dipole? Identify two pairs of perpendicular vectors in the expression.

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 1 - Electric Charges and Field>Text Based Exercises>Q 23

Obtain the expression for the torque

\vec{τ}

experienced by an electric dipole of dipole moment

p

in a uniform electric field

\vec{E}

MEDIUM

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 1 - Electric Charges and Field>Text Based Exercises>Q 23

In the expression for the torque $\vec{τ}$ experienced by an electric dipole of dipole moment $p$ in a uniform electric field $\vec{E}$ . What will happen if the field were not uniform?

EASY

12th CBSE

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New Simplified Physics (Vol 1) For Class 12>Chapter 1 - Electric Charges and Field>Text Based Exercises>Q 23

In the expression for the torque $\vec{τ}$ experienced by an electric dipole of dipole moment $p$ in a uniform electric field $\vec{E}$ . What would happen if the external field $\vec{E}$ is increasing parallel to $\vec{p}$ and anti-parallel to $\vec{p}$ ?

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 1 - Electric Charges and Field>Text Based Exercises>Q 24

An electric dipole is held in a uniform electric field. Using a suitable diagram, show that it does not undergo any translatory motion.

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 1 - Electric Charges and Field>Text Based Exercises>Q 24

An electric dipole is held in a uniform electric field. Derive an expression for the torque acting on it and specify its direction. When is this torque maximum?

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 1 - Electric Charges and Field>Text Based Exercises>Q 25

Define an electric field line. Draw the pattern of the field lines around a system of two equal positive charges separated by a small distance.

EASY

12th CBSE

IMPORTANT

New Simplified Physics (Vol 1) For Class 12>Chapter 1 - Electric Charges and Field>Text Based Exercises>Q 26

What do you understand by electric line of force and give its two important properties.

What do you understand by an electric dipole? Derive an expression for the torque acting on an electric dipole, when held in a uniform electric field. Hence, define the dipole moment.

Important Questions on Electric Charges and Field

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