A new optical illusion has been added to our geometric optics repertoire: A combination of four converging lenses creates a 3D cloaking effect.

... Read more about Paraxial Ray Optics Cloaking

What it shows:

Light is refracted as it passes between two transparent materials of different refractive indices. If the materials are different, but the refractive indices are not, then the light rays are undeviated and the materials are optically indistinguishable.

How it works:

"And if you put a sheet of common white glass in water, still more if you put it in some denser liquid than water, it will vanish almost all together, because the light passing from water to glass is only slightly refracted or reflected or indeed...

A lens immersed in a fish tank of water seems to lose its refractive powers to focus light.

What it shows:

A lens seems to lose its ability to focus when immersed in water. This models the inability of us...

What it shows:

The simplest method of controlling light to form an image is to use an opaque mask with a pinhole in it. Rectilinear propagation of light explains all (nearly). A video camera is substituted for the old prototypal shoe box so that an entire audience can see the pinhole image "live."

How it works:

An extremely light-sensitive video camera ¹ sans lens substitutes for the pinhole camera box and film. The front of the Newvicon is the image plane and, as this sits right behind the faceplate of the camera...

What it shows:

All of the concepts summarized by the above keywords can be clearly and quantitatively demonstrated with this piece of apparatus.

How it works:

A light source ¹ rotates around the circumference of a large white disk ² with degree graduations around the entire perimeter. The collimated beam of light grazes the surface of the disk, creating a highly visible pencil of light, so that ray tracing is easily accomplished. A horizontal mirror, positioned at the center of the disk, is used for the law of...

What it shows:

With an assortment of plane and curved mirrors, convex and concave lenses, parallel-sided block and prisms, the Klinger ¹ Blackboard Optics Kit© allows one to demonstrate all the classic examples in geometric optics by actual ray tracing in two dimensions.

How it works:

All components in the kit are magnetically attached to the blackboard. The light source produces a grazing pencil of light on the surface of the board which may be refracted through, or reflected from, the various optical components. Single...

What it shows:

White light is shown, á la Newton's demonstration of dispersion by a prism, to be composed of a continuous spectrum of colors.

How it works:

A large brilliant spectrum is produced by using a 1 kW carbon arc light source ¹ with adjustable slit, a "fast" f/0.9 imaging lens, ² and a highly dispersive in-line prism. ³ The spectrum easily fills a two meter wide screen with vibrant colors. An alternative (more compact) setup consists of a Beseler slide projector ⁴ which...

Simple RL and RC circuits serve as high-pass and low-pass audio frequency filters.

... Read more about Audio Filters

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...

The visible part of the electromagnetic spectrum is represented by less than an octave of the keys; UV, IR, and microwaves are also indicated.

What it shows:

The keys of a piano are used to represent the electromagnetic spectrum, illustrating the narrow range of frequencies that constitute the portion visible to human sight.

How it works:

An old piano ¹ with its center octave of keys (C₄=261.6Hz to C₅=523.3Hz) colored for the visible spectrum (the seven colors spread to...

Light, passing through heavy glass, has its direction of polarization rotated slightly if a magnetic field is applied to the glass.

What it shows:

When a magnetic field is applied perpendicular to a conductor carrying current, a potential difference is observed between points on opposite sides of the conductor. This happens because the magnetic field deflects the moving electrons (Lorentz force) to the edge of the conductor and the altered charge distribution generates a transverse electric field.

How it works:

The conductor is a small bar (11mm × 2mm × 2mm) of germanium (p-type?). Current (18 mA) is made to flow down the length of the bar by a 3 volt potential...

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...

What it shows:

Stable levitation of one magnet by another is usually prohibited by Earnshaw's Theorem, but the introduction of diamagnetic material at special locations can stabilize such levitation. The demonstration is a replica of an experiment described by M.D. Simon and A.K. Geim¹ and is pictured in the photograph. The illustration is from their paper.

...

What it shows: 

The behavior of a substance in a non-uniform magnetic field will depend upon whether it is ferromagnetic, paramagnetic or diamagnetic. Here we test different substances to see how they are influenced by a magnetic field.

How it works: 

We have a collection of samples (listed in table 1) that exhibit well the three magnetic properties. Diamagnetic substances have a negative relative permeability (susceptibility); paramagnetic substances have positive.

Ferromagnetic substances have...