PX157 - D1c - lenz's law

the effect of an induced emf is such that it opposes the changing flux which produced it

can be derived from faraday's law, from the sign convention that determined the direction of the induced emf

eg: for a moving crossbar

• the motion of the crossbar increases ${\varphi }_B$
• the induced emf is clockwise
• induced current is clockwise
• ampere's law gives that the induced magnetic field is opposite to the original magnetic field
• $|{\overrightarrow{B}}_{ind.}|<|{\overrightarrow{B}}_{ext.}|$ due to finite resistance