Department of Physics and Astronomy
Points of Emphasis
The purpose of this lab is to introduce the students to a number of electric and magnetic phenomena which they will be studying in depth throughout the term. The standard version consists of six lab stations.
Station 1: Electrostatics
This section demonstrates a number of ways that static charges can be created and separated. Activities include: (1) rubbing a rubber rod with cat fur and dipping the rod into balsa chips, (2) rubbing a rubber rod with cat fur and observing what happens to the leaves of an electroscope when the charged rod is brought close and when it is allowed to touch the electroscope, (3) using an electrophorus to induce charges on the electroscope and on to large metal spheres and (4) placing a string wig onto a van de Graff generator and observing what happens when the generator is turned on.
Station 2: Magnetic Eddy Currents
This section demonstrates magnetic forces and the process of magnetic induction. Activities include: (1) running an "aluminum saw" between the poles of an electromagnet both with and without current in the electromagnet and observing the difference in effort needed to move the saw and (2) observing the difference in behavior between a solid and a slotted ring of aluminum when they are allowed to drop between the poles of the electromagnet (with current flowing in the electromagnet).
Station 3: The Oscilloscope
Part I. Students look at Lissajous figures formed by feeding sine waves from two function generators into the X and Y inputs of an oscilloscope. Students can vary the frequency and relative amplitudes of the sine waves to determine the effect on the Lissajous figures.
Part II. Students connect a microphone to an oscilloscope and look at the voltage patterns formed by singing into the microphone, striking a tuning fork, ringing a bell, etc.
Station 4: Standing Waves on a Wire
This section gives the student some direct experience with electric and magnetic acting together. An AC current is produced in a piano wire strung between two post. The wire runs between the poles of a horseshoe magnet (magnetic field perpendicular to the motion of the electron). The oscillating electrons feel a magnetic force perpendicular to both their motion and the magnetic field. This force drives the wire up and down. Students can observe the fundamental and the first five harmonics of the standing waves in the wire. They can also vary the tension in the wire to observe its effect on the fundamental frequency.
Station 5: Electric Currents Produce Magnetic Fields
Part I. Students place a light flexible wire between the poles of a horseshoe magnet and connect the wire to a car battery via a momentary switch. Students are asked to observe what happens to the wire when current from the battery flows through the wire when the momentary switch is depressed.
Part II. Students use a compass needle to examine the magnetic field around a wire in which a current is flowing.
Station 6: Electromagnetic Induction
Part I. Students move a bar magnet in and out of a coil of wire connected to a galvanometer. They are asked to observe how the direction and speed of the motion of the bar magnet effect the indications on the galvanometer.
Part II. Students turn the crank on a small generator and observe the difference in effort required between when the generator is connected to a light bulb and when the generator is disconnected from the light bulb.
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