Motional EMF and Magnetic Braking
Move a conducting rod through a magnetic field and connect its signed induced current to braking force and resistive heating.
Free theory articleMove a conducting rod through a magnetic field and connect its signed induced current to braking force and resistive heating.
Concept & interpretation
When a conducting rod oriented along +y translates with velocity vx along +x through a uniform magnetic field Bz along +z, the magnetic Lorentz force on mobile charge carriers generates a motional electromotive force (EMF) given by Vtop − Vbottom = −BzLvx. Closing the loop through an external stationary circuit of total resistance R drives an upward rod current I = EMF / R and produces a magnetic braking force Fx = ILBz = −Bz2L2vx / R that opposes motion while converting mechanical work into Joule heating.
Experiment
Explore the relationship between motion, magnetic field polarity, and induced braking forces in the Motional EMF and Magnetic Braking module:
- Set Field Bz to 1, Rod length L to 1, Velocity vx to 2, and Resistance R to 2. Verify the −2 V EMF and the −1 N magnetic braking force opposing motion.
- Change Field Bz to −2, Rod length L to 1/2, and Resistance R to 1. Notice the EMF reverses sign to 2 V and upward current becomes 2 A, while the magnetic force Fx = −2 N still opposes the positive velocity.
- Reverse the motion by setting Velocity vx to −2 (with Bz = 2, L = 1, R = 4). The EMF becomes 4 V and the magnetic force becomes +2 N, opposing motion in the −x direction.