Free Electric Field MCQs with Answers
4 Electric Field MCQs from Physics, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
4 questions
1. Electric field lines
- A. can cross one another
- B. start on negative charges and end on positive charges
- C. never cross, because the field has only one direction at each point
- D. are always straight
Explanation: Two crossing lines would mean two different field directions at the same point, which is impossible for a single resultant vector. Lines run from positive to negative charge, and their spacing represents the strength of the field. They are straight only for simple arrangements such as an isolated point charge or a uniform field.
Correct answer: never cross, because the field has only one direction at each point2. Inside a hollow charged conductor in electrostatic equilibrium, the electric field is
- A. zero everywhere
- B. maximum at the centre
- C. equal to the field just outside
- D. directed towards the centre
Explanation: Charges on a conductor arrange themselves on the outer surface until the field inside cancels completely; any residual field would move the free electrons until it did. This is the basis of the Faraday cage, which is why a car is a relatively safe place in a lightning storm and why sensitive equipment is shielded in metal boxes. The field just outside the surface, by contrast, is not zero.
Correct answer: zero everywhere3. Charge on a charged conductor resides
- A. uniformly throughout its volume
- B. on its outer surface, concentrating most where the surface is sharply curved
- C. at its centre
- D. only where it was first placed
Explanation: Mutual repulsion drives the charges as far apart as possible, so they collect on the outside, and the surface charge density is highest at points and edges. This concentration produces the very strong field that ionises the surrounding air at a sharp point, which is the principle of the lightning conductor. Inside the metal the field remains zero.
Correct answer: on its outer surface, concentrating most where the surface is sharply curved4. An electric dipole placed in a uniform electric field experiences
- A. a net force but no torque
- B. a torque but no net force
- C. neither force nor torque
- D. both a large net force and a torque
Explanation: The equal and opposite charges feel equal and opposite forces in a uniform field, so the forces cancel, but because they act along different lines they form a couple that turns the dipole into alignment with the field. In a non uniform field the two forces differ in size and a net force does appear. This turning effect is how polar molecules align in a dielectric.
Correct answer: a torque but no net force