#  Induction and Faraday's Law 

 



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### Faraday's Law

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A bar magnet or other source of magnetic field induces a current in a coil of wire when the magnetic flux through the coil changes.  
\[[In-Depth Description](/presentations/faradays-law)\]

### Induced EMF

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A small light bulb, in series with a coil, lights up when brought close to an AC energized solenoid.

### Back EMF

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A light bulb, wired in parallel across an inductor, momentarily glows intensely when the DC current is switched off.   
\[[In-Depth Description](/presentations/back-emf)\]

### Hand Cranked AC Generator

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Observe the induced current in a gimbaled coil as it rotates in Earth's magnetic field.  
\[[In-depth description](/presentations/hand-cranked-ac-generator)\]

### Welding Transformer

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Step-down transformer with enough current to heat and fuse iron nails.   
\[[In-Depth Description](/presentations/welding-transformer)\]

### Motional emf

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Show the emf induced in a wire vibrating in a magnetic field and electrify the acoustic tonometer.  
\[[In-Depth Description](/presentations/motional-emf)\]

### Jump Rope Induction

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The earth's field induces an EMF in a long wire swung around in jump rope fashion.

### Ring Flinger Lenz's Law

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A ring conductor, surrounding the iron core of a solenoid, is repelled and flung into the air when the coil is energized.  
\[[In-Depth Description](/presentations/ring-flinger-lenzs-law)\]

### Can Crusher - Magnetic Implosion

\[L | t+ | ★★★★\]   
An empty aluminum soft drink can, placed inside a coil of wire, is made to implode when a capacitor is discharged through the coil.  
\[[In-Depth Description](/presentations/can-crusher-magnetic-implosion)\]

### Attractive and Repulsive Phases

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A 60 Hz AC magnetic flux induces an emf in a coil of wire. With appropriate capacitance added, the coil will be attracted to, repelled from, or not affected by the magnetic flux.  
\[[In-Depth Description](/presentations/attractive-and-repulsive-phases)\]

### Cylinder Drop Lenz's Law

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Two seemingly identical cylinders are dropped down a vertical aluminum tube; the magnetic one falls very slowly.

### Eddy Current Damping

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Sheets of aluminum, dropped between the poles of a large magnetron magnet, fall "slowly" to the ground.  
\[[In-Depth Description](/presentations/eddy-current-damping)\]

### Eddy Current Pendulum

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Large copper paddles, one solid and one slotted, swinging between poles of electromagnet.   
\[[In-Depth Description](/presentations/eddy-current-pendulum)\]

### Resistance to Eddy Currents

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Drop magnetic rings over copper, brass, aluminum, and stainless steel rods to show how electrical resistance affects eddy current damping.

### Eddy Current Levitation

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A large rare-earth magnet is attracted to, and quasi-statically levitated, by another rare-earth magnet held above it.  
\[[In-Depth Description](/presentations/eddy-current-levitation)\]

### Magnetic Levitation

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A large rare-earth magnet, tethered over an aluminum disk, is made to levitate when the disk spins.  
\[[In-Depth Description](/presentations/magnetic-levitation)\]

### Eddy Currents at LN2 Temperature

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A magnet, dropped onto a block of copper cooled to LN2 temperature, bounces like a ball.  
\[[In-Depth Description](/presentations/eddy-currents-ln2-temperature)\]

### Contact Us

**Mailing Address**: Lecture Demonstration Services, Science Center, Rm B-08A, 1 Oxford Street, Cambridge, MA 02138  
**Campus Location**: Science Center B-08A | **Tel**: (617) 495-5824 | **Email**: scidemos-at-fas.harvard.edu