# Simplifying Lenz's Law

## Main Question or Discussion Point

I am having great difficulty grasping the concept of Lenz's law. As far as I am unware it is derived as:

"any current driven by an induced e.m.f opposes the change causing it"

I do not really understand what this means - help would be greatly appreciated :)

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The law of Lenz can be described as follows:

Induced quantities, such as current (mmf), voltage (emf), flux, & torque, are always oriented in a direction opposite to the original quantities.

A motor is started. It's current draw is large when at a standstill. Once the rotor spins, mmf/emf are induced into the stator. This induced current opposes the original current. Hence the net current draw decreases.

If I pedal a bicycle type generator under no load, and I control the speed to 300 rpm, for example. I then load the generator with 50 watts. The added load current has a magnetic field which produces a an additional torque. This torque counters my pedaling torque.

Otherwise, a motor or generator would create its own supply of energy. Induced quantities, electrical as well as mechanical, always act in the *opposite direction* to the corresponding original quantities.