Driven RLC Circuit

rlc circuit

What It Shows

The amplitudes and relative phases of the voltages across the individual elements of a series RLC circuit varies with the frequency of the driving voltage. The voltages of the three elements plus the driver are plotted simultaneously on an...

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Electromagnetic Spear

What it shows:

Static 3-D stylized model of an electromagnetic wave, with two sets of sinusoidal fins at 90° representing the E and B fields.

How it works:

The wave packet model consists of a wooden spine with E and B fins of 1cm wooden dowels. A plastic arrowhead gives the spine a direction.

Figure 1. The Spear


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The Barkhausen Effect

What it shows:

The magnetization of a ferromagnetic substance occurs in little jumps as the magnetic moments of small bunches of atoms, called domains, align themselves with the external field. We can actually "hear" the switching of these domains by amplifying the currents induced in a coil that surround the ferromagnetic material.

How it works:

We use two 10mH coils mounted back-to-back to cut out AC noise. The samples, listed in Fig.1 are in wire form, about 3-5cm in length and pushed through corks so they can sit...

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Paramagnetism of Oxygen

What It Shows

A large magnet with a small cylindrical gap allows a stream of liquid nitrogen to pass over and through. Poured liquid oxygen hangs between the poles in the strong field until it boils away.

How It Works

Pour the liquid nitrogen first, slowly over the pole pieces. The result is nothing but vapor condensation and crackling plexiglas; the liquid does not interact with the large magnetic field.

Next pour the liquid oxygen slowly over the pole pieces, and it collects in the gap between the poles. It might take two or three short pours to get the...

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Skin Depth

What it shows:

The depth to which electromagnetic radiation can penetrate a conducting surface decreases as the conductivity and the oscillation frequency increase. This demo compares the skin depth of AM and FM radio frequencies, and shows just how small these distances are.

How it works:

An electromagnetic wave entering a conducting surface is damped and reduces in amplitude by a factor 1/e in a distance ∂ given by 1


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Eddy Current Damping

What it shows:

A sheet of aluminum falls slowly between the poles of a magnet because induced currents in the sheet set up magnetic fields which oppose the motion.

How it works:

As the aluminum sheet falls between the poles of the magnet, eddy currents are induced in the metal. These currents set up their own magnetic fields, which through Lenz's law oppose the change that caused them. As the cause is gravity pulling the sheet to Earth, the sheet decelerates as it passes between the poles of the magnet, only to accelerate again...

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Ring Flinger Lenz's Law

What it shows:

A changing magnetic flux induces a current in a metal ring; the magnetic field due to this current opposes the primary field, repelling the ring and flinging it into the air. That's the simple "hand waving" explanation for the beginner student—a more accurate explanation follows.

How it really works:

The jumping ring is a vivid and popular demonstration of electromagnetic induction and is used to illustrate Faraday's and Lenz's laws. A conducting ring, placed over the ferromagnetic core of a solenoid, may levitate or...

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Motional emf

What it shows

An emf is induced between the ends of a wire moving back and forth in the presence of a magnetic field.

How it works

The ends of a monochord wire are connected to an oscilloscope as illustrated:

Motional emf

Plucking the wire...

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Hand Cranked AC Generator

Observe the induced current in a gimbaled coil as it rotates in Earth's magnetic field.

What it Shows

A changing magnetic flux through a circular coil of wire induces a current in the wire. By spinning a circular coil of wire at constant frequency and measuring the induced voltage across its ends we can find the local direction and magnitude of the Earth's magnetic field as it passes through the coil. The commutators of the coil are configured to produce an alternating current.


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Back EMF

What it shows:

A sudden change in current in an inductor - resistor circuit produces a very large back EMF. If that resistance is a bulb, it will shine much brighter during the change than during DC flow.

E = -LdI/dt

How it works:

The circuit consists of a 6V bulb connected in parallel with a 10.5mH inductor coil as in figure 1. With the battery connected, the bulb burns at its rated 6V. Disconnecting the battery sends the applied voltage and hence the current to zero. The rapidly collapsing...

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