Physics notes for Class 12 | CBSE NCERT Solutions | Electric Dipole
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Electric Dipole: A system containing two equal and opposite charges separated by a finite distance is called an electric dipole.
Electric Dipole moment: Electric dipole moment is defined as the product of magnitude of one of the charges and length of the dipole say ‘2a’ i.e.
- The electric dipole moment is a vector quantity.
- It is directed from – q to + q i.e.from negative charge to the positive charge.
- SI unit of electric dipole moment isCoulomb- meter (Cm).
- The net charge on an electric dipole is zero.
Electric force and Torque on an Electric dipole in a uniform electric field:
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Consider an electric dipole placed in a uniform electric field of strength E.The net electric force is zero but a torque is experienced by the dipole. So, the dipole will rotate till it becomes parallel to the electric field.
Now torque = Force × perpendicular distance
= qE× BC
= qE × 2a SinƟ
= (q × 2a)E SinƟ
Torque in vector form is
- The total force on an electric dipole placed in a uniform electric field is zero.
- Maximum value of torque acting on the dipole is when Ɵ = 900
Torque = pE × Sin 900
= pE × 1
Question: What happens when an electric dipole is placed in a non-uniform electric field?
Ans: When an electric dipole is placed in a non-uniform electric field, the dipole will have both rotational and translational motion. When the dipole becomes parallel to the electric field, the rotational motion will stop.
Question: An electric dipole consists of a positive and negative charge of 4µC each placed at a distance of 5mm.Calculate dipole moment.
q = ±4µC = ±4 × 10-6C
p = q x 2a
2a = 5mm = 5 × 10-3 m
= 4 × 10-6 × 5 × 10-3
= 2 × 10-8 C- m