MCAT Physics Question 75: Answer and Explanation

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Question: 75

15. A dipole is placed in an electric field and is allowed to come to equilibrium. How would the dipole react if the direction of the electric field is suddenly reversed?

  • A. It rotates to align with the new field.
  • B. It accelerates linearly along the field lines.
  • C. It experiences no rotational or linear movement.
  • D. It both rotates to align with the new field and accelerates linearly along the field lines.

Correct Answer: C

Explanation:

Torque is a function of both force applied and the angle at which it is applied. A dipole placed in an electric field will experience a torque until it comes to rest oriented within the field, at which point the angle between the plane of the dipole and the electric field is 0°. Once this point is reached, inverting the electric field has no impact on the dipole because it will now have an angle of 180°, the sine of which is still 0.

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