Electric Dipole and Dipole Moment - UNSOLVED PRACTICE SET
Chapter: Electric Charges and Fields | Topic: Electric Dipole and Dipole Moment
ELECTRIC DIPOLE AND DIPOLE MOMENT - UNSOLVED PRACTICE SET
Topic: Electric Dipole and Dipole Moment
Multiple Choice Questions
Q1. An electric dipole consists of:
- Two equal positive charges separated by a distance
- Two equal negative charges separated by a distance
- Two equal and opposite charges separated by a small distance
- Any two charges separated by any distance
Q2. The SI unit of electric dipole moment is:
- C m
- N m
- V m
- J/C
Q3. The direction of the electric dipole moment is:
- From negative charge to positive charge
- From positive charge to negative charge
- Perpendicular to the line joining the charges
- Along the bisector of the angle between the charges
Q4. When an electric dipole is placed in a uniform electric field, the net force on the dipole is:
- Maximum
- Zero
- Depends on the angle
- Equal to qE
Q5. The torque experienced by an electric dipole in a uniform electric field is maximum when the angle between the dipole moment and the field is:
- 0°
- 45°
- 90°
- 180°
Q6. The potential energy of an electric dipole placed parallel to a uniform electric field is:
- Maximum
- Zero
- Negative
- Positive
Short Answer Questions
Q7. Define electric dipole moment. Write its expression in terms of charge and separation distance.
Q8. Why is a water molecule considered an electric dipole? Explain with its structure.
Q9. An electric dipole is placed in a uniform electric field making an angle θ with the field. Write the expression for the torque experienced by the dipole.
Q10. In which orientation of an electric dipole in a uniform electric field is it in
(a) stable equilibrium, and
(b) unstable equilibrium?
Q11. Why does an electric dipole experience a torque but not a net force when placed in a uniform electric field?
Q12. The dipole moment of a system is 4 × 10⁻⁹ C m. If the separation between the charges is 2 cm, what is the magnitude of each charge?
Long Answer Questions
Q13. Derive an expression for the torque experienced by an electric dipole placed in a uniform electric field. Explain the conditions for maximum and minimum torque.
Q14. Derive an expression for the potential energy of an electric dipole in a uniform electric field. Show that the potential energy is minimum when the dipole is aligned with the field.
Q15. An electric dipole consists of charges ±5 μC separated by a distance of 2 cm. It is placed in a uniform electric field of 2 × 10⁴ N/C.
(a) Calculate the dipole moment.
(b) Find the maximum torque experienced by the dipole.
(c) Calculate the work done in rotating the dipole from θ = 0° to θ = 90°.
Numerical / Application-Based Problems
Q16. An electric dipole has charges +2 μC and −2 μC separated by a distance of 4 cm.
(a) Calculate the dipole moment.
(b) The dipole is placed in a uniform electric field E = 3 × 10⁴ N/C, making an angle of 30° with the field. Calculate the torque on the dipole.
(c) How much work must be done to rotate the dipole from 30° to 180°?
Q17. In a biology class, you learn that the human heart generates electrical signals that can be detected. Imagine modeling a small region of heart tissue as an electric dipole with dipole moment p = 2 × 10⁻¹¹ C m, placed in the body's natural electric field of E = 1 N/C.
(a) Calculate the maximum torque on this dipole.
(b) If the dipole rotates from alignment with the field (θ = 0°) to perpendicular (θ = 90°), how much work is done by the field?
(c) Explain why understanding dipoles is important in medical applications like ECG.
Q18. Two point charges +q and −q are placed at points A(0, 0) and B(4 cm, 0) respectively.
(a) Calculate the dipole moment of the system.
(b) Find the electric field at a point P on the perpendicular bisector of AB, at a distance of 3 cm from the midpoint.
(c) Compare the magnitude of this field with the field at a point on the axial line at the same distance from the center.
[Given: k = 9 × 10⁹ N m² C⁻², q = 2 μC]