Faraday–Lenz motion EMF: If a straight conductor is moved back and forth at a constant speed within a uniform magnetic field, the induced voltage in the conductor reverses polarity as the direction of motion reverses. True or false?

Introduction / Context:
Electromagnetic induction governs how motion in a magnetic field produces voltage. This principle is used in generators, pickups, and many sensors. Recognizing how polarity depends on motion direction is key to correct wiring and signal interpretation.

Given Data / Assumptions:

• A uniform magnetic flux density B is present.
• A straight conductor of length l moves back and forth at constant speed v.
• The motion is perpendicular to both B and the conductor's length for maximum EMF.

Concept / Approach:

The motional EMF magnitude is E = B * l * v when motion, field, and conductor orientation are mutually perpendicular. Polarity follows the right-hand rule (or Fleming's right-hand rule): reversing velocity v to −v reverses the cross product direction and thus the induced polarity at the conductor ends.

Step-by-Step Solution:

Verification / Alternative check:

Connect the moving conductor to a voltmeter via slip contacts. Sweep the bar forward then backward; observe the meter deflection switch direction, confirming polarity reversal consistent with Lenz's law.

Why Other Options Are Wrong:

• “False” would imply polarity is independent of motion direction, which contradicts the vector nature of v × B and the conservation principle embedded in Lenz's law.

Common Pitfalls:

Not maintaining orthogonal geometry (reduces EMF), confusing sign conventions, or neglecting that non-uniform B fields can change magnitude as well as polarity behavior.

Final Answer:

True