Home › UP Board Class 12 › Magnetism & EMI › Eddy currents in the metallic rails ahead of a m…
Eddy currents in the metallic rails ahead of a moving train can be used for magnetic braking because:
AThey create a magnetic field that levitates the train
BThey convert kinetic energy into electrical energy fed back to the train
CThey exert a force on the train in the direction of motion
DThey oppose the change in flux and therefore the motion, dissipating energy as heat
Answer & Solution
Correct answer: D. They oppose the change in flux and therefore the motion, dissipating energy as heat
By Lenz's law the eddy currents induced in the rails by the train's electromagnet flow in a direction that opposes the change in flux. The associated $\vec{I}\times\vec{B}$ force opposes the motion of the train, while the eddy currents themselves dissipate energy as Joule heat in the rails. This is non-contact braking with no mechanical wear.
Related questions
A storage battery of emf 8.0 V and internal resistance 0.5 $\Omega$ is charged by a 120 V The number density of free electrons in a copper wire is $8.5 \times 10^{28}\ \text{m}^{-3A heating element has resistance 100 $\Omega$ at 27.0 °C. Its temperature coefficient of rA wire of length 15 m and uniform cross-section $6.0 \times 10^{-7}\ \text{m}^2$ has a meaThe statement "$V = IR$ is itself the statement of Ohm's law" is, according to the text, iCurrent through an area of cross-section is treated as a scalar quantity in this chapter eA Wheatstone bridge has arms AB = 100 $\Omega$, BC = 10 $\Omega$, CD = 5 $\Omega$, DA = 60In a Wheatstone bridge the unknown resistance is placed in the fourth arm. Known resistanc