natural sciences
lecture demonstrations
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Electricity and Magnetism

  1. Electrostatics
    • Triboelectric Effects Ebonite rod/fur, or glass rod/silk, to generate static charges. (m) (T) ***
    • Induced Electric Dipole Neutral Styrofoam puffs are attracted and picked up by charged rod. (m) (T) **
    • Electroscope Gold leaf projection or large arm balance versions of qualitative electrometers. (s/m) (T) ****
    • Conservation of Charge A neutral system of charges is rearranged...charge measured on one part is equal and opposite to the charge on another part. (m) (T+) ***
    • Coulomb's Law. Charged, helium-filled balloons repel and/or attract each other. (l) (T+) A small apparatus also shows the effect more quantitatively. (s) (T)
    • Hair-raising Wig or hippy volunteer, use a Van de Graaff generator to make your hair repulsive. (m) (T) ****
    • Electrostatic Bells. Electically charged bells are repeatedly struck by a small ball which is alternately attracted and repelled by them. (s) (T)
    • Electrostatic Motor. Ping-pong ball oscillates inside parallel plate capacitor. (m) (T+).
    • Wimshurst Machine. Antique electrostatic generator. (m) (T)
    • Kelvin Water Dropper. Unique electrostatic generator...Purcell's analog of Wimshurst. (m) (T+)
    • Van de Graaff Generator. Anti-antique electrostatic generator to be used with pie plates, etc. or just as a demonstration by itself (of static electricity generation). (l) (T+)
  2. Electric Fields Around Conductors
    • Electric Field Patterns. Visualization of various electrostatic fields on OHP. (s) (T)
    • Faraday Ice Pail and Cage. Used in conjunction with an electrometer, this ensemble provides quantitative measurements for a variety of electrostatic experiments. (l) (T+)
    • Coke Can Attraction. A neutral coke can rolls across the lecture table as it is attracted to a charged rod. (m) (T)
    • Surface Charge Densities. Charged, conductive solids can be probed to determine charge densities...used with Faraday ice pail and cage. (l) (T+)
    • Whirlygig. A lawn sprinkler style rotor with pointed ends becomes an electrostatic motor when brought to high potentials. (m) (T)
    • Force on an Electric Dipole. A freely suspended electric dipole aligns itself with the electric field (provided by two large, charged capacitor plates). (s) (T+)
    • Field Inside Conductor. Charged, hollow conductor is probed to demonstrate the absence of an electric field inside. (l) (T+)
    • Walk-In Faraday Cage Sit in it and get raised to high potentials. (l) (T+) ****
    • Electrostatic Shielding. Is it a two-way street? No. (s) (T++)
    • Capacitors. Selection of different capacitor types for quantitative measurements as well as show 'n tell. (s/m) (T)
    • Giant Capacitor Parallel plate capacitor (1m dia.) with variable plate separation. (l) (T+) ***
    • Force on a Conductor. A suspended conductor is pulled into a parallel plate capacitor when charged. (l)(T+)
    • Energy Stored in Capacitor Capacitor drives motor which raises a mass. (m) (T+) **
    • Explosive Capacitor Discharge. The energy stored in a capacitor is dramatized by discharging it through a wire shorted across the capacitor. (l) (T++)
    • One Farad. State-of-the-art capacitor makes impressive charge storage container; with suitable light bulb, RC is visibly long! (s/m) (T+)
  3. Electric Currents; DC Circuits
    • Conductivity of Water Add salt to water to make it conduct and light a bulb. (m) (T+) **
    • Conductivity of Copper. Light bulb gets brighter when copper leads are immersed in liquid N2 (positive temperature coeffient). (m) (T+) **
    • Conductivity of Glass. Insulating glass becomes a conductor of electricity when heated red-hot with a blowtorch. (m) (T++)
    • Conductivity of Carbon. Light bulb gets dimmer when carbon resistor (in series) is immersed in liquid N2 (negative temperature coefficient). (m) (T+)
    • Conductivity of a Flame. An electroscope is discharged when a burning candle is brought near it. (m) (T)
    • Conductivity of Air. Electric conduction of air is demonstrated by Jacob's ladder. (m) (T)
    • IV Curves. A Tektronix "curve tracer" shows I vs V for resistor, germanium diode, silicon diode, or tunnel diode. (s/m) (T+)
    • Hand Battery Copper and zinc plates connected by m-ammeter; your hand completes the circuit. (s) (T)
    • Lead Acid Battery Homemade chemistry-lab style battery in a beaker. (m) (T+)
    • Organic Battery Use a selection of fruit to produce a voltage. (m) (T++)
    • Thermo-electric Magnet. A large current-capacity thermocouple junction powers an electromagnet. (m) (T++)
    • Piezo-electric Sparker. Generate high voltages by squeezing a crystal. (m) (T)
    • Bird-on-a-Wire A model to help explain why birds don't get zapped on high-voltage transmission lines. (m) (T) **
    • Lossy (or lousy) Transmission Line. Several light bulbs are wired in parallel; the resistance of the wire leads to appreciable I2R losses. (m) (T)
    • High Voltage Transmission Line. Power to a 100 W light bulb is transmitted throughhairlike wires; 15 kV step-up and step-down transformers do the trick. (m/l) (T++)
    • OHP Circuit Board For construction of simple DC circuits. (s) (T) ***
    • DC Circuit Puzzlers to Ponder. Simple circuits with batteries, light bulbs, and switches challenge one's understanding. (m) (T)
    • Large Voltmeter/Ammeter Board. An application of series and parallel resistance circuits. (l) (T)
    • RC Time Constant Pre-assembled circuit board; displays RC time constant on CRO. (l) (T+) ***
    • RL Time Constant Pre-assembled circuit board; displays RL time constant on CRO. (l) (T+) ***
  4. Fields of Moving Charges
    • Maltese Cross CRT Maltese Cross obstacle and fluorescing glass show that electrons travel in straight lines and are affected by magnetic fields. (m) (T) ***
    • Cathode Ray Deflection Small Crookes tube with built-in fluorescent screen shows electron beam deflection by magnetic field. (m) (T) ***
    • TV Image Deflection Image on black and white television is deflected by a magnet, not unlike the Maltese Cross. (l) (T+) **
    • Flicker Bulb. A magnet placed near this commercially available light bulb causes the filament to vibrate at 60 Hz, producing a "flickering" effect. (m) (T)
    • e/m Apparatus. An electron beam is deflected into circular or spiral paths by a magnetic field. (l) (T+)
    • Force Between Parallel Conductors. Truck battery and cable loop. (l) (T+)
    • Jumping Wire Motor effect on conductor between poles of horseshoe magnet. (l) (T+) ***
    • Magnetically Accelerated Axle. Current carrying axle on rails experiences force from electromagnet. (l) (T+)
    • Current Carrying Electrolyte. Electrolyte circulates in magnetic field. (s) (T+)
    • Mercury Fountain. Inverse MHD (magneto-hydrodynamic generator). (l) (T++)
  5. Magnetic Fields
    • OHP Magnetic Lines of Force Bar magnet and/or various current-carrying wire configurations; sprinkled iron filings reveal the lines of force. (s) (T) **
    • Dipole in a Magnetic Field. A suspended current-loop dipole experiences torques in a magnetic field provided by Helmholtz coils. (m/l) (T)
    • Magnetic Field of a Solenoid. A large compass is used to map out the field of a giant solenoid. (l) (T+)
    • Magnetic Field of Current Loop A large compass is used to map out the field of a giant copper loop. (l) (T+)
    • Oersted's Experiment Five large compasses, placed around a vertical copper pipe, indicate the magnetic field when the current is turned on. (l) (T+) ***
  6. Induction and Faraday's Law
    • Faraday's Law. Demonstrated by changing the magnetic flux through a coil, using either a bar magnet or another current-carrying coil. (m) (T+)
    • Induced EMF. A small light bulb, in series with a coil, lights up when brought close to an AC energized solenoid. (m) (T)
    • Back EMF A light bulb, wired in parallel across an inductor, momentarily glows intensely when the DC current is switched off. (m) (T) **
    • Jump Rope Induction. The earth's field induces an EMF in a long wire swung around in jump rope fashion. (m) (T)
    • Ring Flinger Lenz's Law A ring conductor, surrounding the iron core of a solenoid, is repelled and flung into the air when the coil is energized. (m) (T) ****
    • Cylinder Drop Lenz's Law. Two seemingly identical cylinders are dropped down a vertical aluminum tube; the magnetic one falls very slowly. (m) (T)
    • Eddy Current Damping Sheets of aluminum, dropped between the poles of a large magnetron magnet, fall "slowly" to the ground. (m) (T) ***
    • Eddy Current Pendulum Large copper paddles, one solid and one slotted, swinging between poles of electromagnet. (l) (T+) ***
    • Magnetic Levitation A large rare-earth magnet, tethered over an aluminum disk, is made to levitate when the disk spins. (l) (T) ***
    • Eddy Current Pinch. Eddy currents induced in a Coke can cause it to violently collapse. (l) (T++)
  7. Electric Fields in Matter
    • Dielectrics in Capacitors Parallel plate capacitor and capacitance meter with insertable dielectrics. (m) (T+) ***
    • Temperature Dependance of Permittivity. Liquid dielectrics in parallel plate capacitor are heated to demonstrate temperature effects. (s/m) (T+)
    • Thermoelectric Effect. Thermocouple junction produces EMF with enough current compliance to energize an electromagnet. (s/m) (T+)
    • Skin Depth KISS (108 MHz) electromagnetic waves penetrate aluminum box while HDH (680 KHz) waves don't. (m) (T) **
    • Exploding Capacitor. Electrolytic capacitor connected with reversed polarity to a far too large voltage source. (m) (T+)
  8. Magnetic Fields in Matter
    • Para and Diamagnetism Testing a selection of compounds for magnetic susceptibility, by suspending them between the poles of an electromagnet. (l) (T+) ***
    • Paramagnetism of Oxygen. Liquid O2 is attracted to magnet. (s/m) (T++)
    • Hysteresis. Hysteresis loops of iron and ferrite are displayed on CRO. (m/l) (T+)
    • Barkhausen Effect Hear the sound of magnetic domains aligning as a bar magnet is brought towards iron sample. (m) (T+) ***
    • Magnetic Bubbles Wafer thin magnetic garnet under microscope reveals direction of magnetic domain alignment as light and dark pattern. (s) (T+) **
    • Bar Magnet Domains. Magnetic domains are modeled on the OHP. (s) (T)
    • Curie Point. Iron wire is not attracted to a magnet when its temperature is raised above 770°C. (m) (T+)
    • Hall Voltage. The Hall voltage of a semiconductor is measured as a function of applied magnetic field. (l) (T++)
  9. Electromagnetic Waves
    • Electromagnetic Spear Three dimensional model showing B-field and E-field of electromagnetic radiation. (m) (T) **
    • Group/Phase Velocity. The group velocity of two harmonic waves can be shown (on an oscilloscope) to be less than or greater than the individual phase velocities. (m) (T+)
    • Hertz Resonator Production and detection of electromagnetic waves using LC oscillator; transmission and detection inductors are 1m diameter copper rings. (l) (T+) ****
    • Microwave Generator. 10 cm microwaves are used for the demonstration of travelling and standing waves, reflection, refraction, diffraction, and polarization. (l) (T+)
    • Tesla Coil. Extremely high voltages are generated by the application of a resonant circuit and tuned antenna. (m) (T)
    • Dipole Radiation. The radiation pattern from a 1/2 wave dipole antenna can be explored with a transistor radio (100 MHz, FM). (l) (T+)
    • FM Standing Waves. Electromagnetic waves reflecting off the blackboard interfere with incoming waves to produce standing waves. (l) (T++)
    • Piano The visible part of the electromagnetic spectrum is represented by less than an octave of the keys; UV, IR, and microwaves are also indicated. (l) (T) ***
  10. Electromagnetic Devices
    • Barlow's Wheel. A copper disk, supported between two magnet poles, rotates when a DC current is passed radially through it. (m) (T+)
    • Miller-Cowan Motor/Generator. Working model of electric motor and/or generator with solid and split-ring commutator  (m) (T)
    • Motor/Generator Pair. Two, small, permanent magnet, hand-cranked electric motors are wired together and operate interchangeably as motor or generator. (s) (T)
    • Military Field Generator. Hand-cranked generator allows student to feel and appreciate power production when a small load (25 watt bulb) is connected. (m) (T)
    • Mercury MHD Generator. Mercury, pumped through a tube transverse to a magnetic field, produces an electric current; magnetohydrodynamic generator. (m) (T+)
    • Welding Transformer Step-down transformer with enough current to heat and fuse iron nails. (m) (T+) ***
    • Transmission Line Transformers. 15,000 volt step-up/step-down shows how high power can be transmitted along extremely small wire. (m) (T+)
    • Tesla Coil. Extremely high voltages are generated by the application of a resonant circuit and tuned antenna. (m) (T)
  11. AC Circuits
    • OHP RLC Circuit KiloHenries and microFarads allow one to see the current slosh back and forth in this circuit. (s) (T) ***
    • RLC Resonance Circuit. Amplitudes and phases of voltages across all circuit elements are displayed simultaneously on CRO; frequency is adjustable. (l) (T+)
    • Driven RLC Circuit. Response of RLC circuit as a function of sweapt frequency is observed on an oscilloscope. (m) (T+)
    • LC Piano. An "electric" piano; tunes are played by changing L. (l) (T)
    • RLC Tunable Circuit. Energized by 60 Hz line voltage, this circuit can be tuned with a movable iron core in the inductor; the R is a light bulb. (m) (T)
    • RLC Bridge Circuit. An LC bridge circuit with light bulbs providing the R's; the bridge is balanced visually as indicated by light bulb brightness. (m) (T+)
    • AC/DC Power. When a DC voltage is equal to the rms value of a sinusoidal voltage, the powers supplied to separate light bulbs are equal. (M) (T++)
    • Tesla Coil. Extremely high voltages are generated by the application of a resonant circuit and tuned antenna. (m) (T)
    • Dust Particle Paul Trap. An electrically charged dust particle is trapped in a time-varying (60 Hz) quadrupole electric field. (s) (T+)