# Induced EMF and Lenz’s law #### Everything You Need in One Place

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##### Intros
###### Lessons
1. Induced emf
2. The relative motion between the magnet and coil induces current (Lenz's law).
##### Examples
###### Lessons
1. A bar magnet is moving toward a solenoid. What is the direction of the current through the galvanometer and what is the the direction of the magnetic field produced by thus current at location P inside the solenoid? 1. A magnet is moving toward an aluminum ring. In which way will the current flow in the labelled portion of the ring as the magnet moves towards the ring?

1. Towards 1
2. Towards 2
3. Towards 3
4. Towards 4
1. A coil moves at a constant velocity across a region of magnetic field as shown. Which of the following best shows the emf vs. time graph for the emf induced in the coil as it moves from 1 to 2? 1. A conductor is moved to the right through four magnetic field as shown below. In which case will the largest emf be generated? 1. A bar magnet is moved away from a coil as shown. What is the direction of the current through the resistor and polarity of the left end of the coil? 1. In which of the following situation would the greatest emf be induced in the coil? All changes occur in the same time interval. ###### Topic Notes

In this lesson, we will learn:

• A changing magnetic field induces current
• Direction of the induced current depends on the direction of the motion of the magnet with respect to the coil.
• No current is induced if the magnet does not move relative to the coil.
• It is the relative motion between the magnet and coil that counts.
• Lenz’s law

Notes:

Induced EMF
• The purpose of this concept is to produce an electric current from a magnetic field.
• A coil of wire, $X$, is connected to a battery. A magnetic field is produced by the current that flows through the coiled wire $X$ and is intensified by the iron core.
• The current in the second coiled wire, $Y$, is the result of change in magnetic field. The current is detected by the galvanometer only when switch is closed or opened.
• Constant current in $X$ produced constant magnetic field, which produces NO current, but changing the magnetic filed can produce an electric current in coil $Y$.
• Such current is called the induced current. Changing magnetic field through coil $Y$, produces an electric current in the coil.

• a changing magnetic field NOT the magnetic field itself, induces an emf” The relative motion between magnet and coil induces the current

Lenz’s law;
A current produced by an induced emf moves in a direction so that its magnetic field opposes the original change in flux.

• Magnet is pushed into the coil

• • Magnet is pulled out of the coil

• • Stationary magnet

• 