Solenoid Switch. Purpose To demonstrate electromagnetism and to explore terminology associated with magnets and electromagnets.

Transcription

1 Experiment D Solenoid Switch Purpose To demonstrate electromagnetism and to explore terminology associated with magnets and electromagnets. To introduce Lenz s law and Faraday s law. To discover terms such as: magnetic flux, lines of force, magnetic fields, poles, ferromagnetic retentivity, hysteresis, induction, and saturation. To include both pictorial and schematic diagrams of the experiments. What s Going On? Everyone in all groups should read the Student Handout Electromagnetism and Introduction to Electronics and Alternating Current. Electromagnetic Experiments When current flows through a wire a small magnetic field is created. By coiling the wires around and around in layers, this electromagnetic effect is increased. When combined with an easily magnetized material like iron or steel, or placed near a natural magnet, work (energy) is produced. The solenoid, which is a magnetic switch; the galvanometer which is a magnetic compass detecting current flow; the motor, which turns around; or the electromagnet, which can pick up iron and steel are all examples of a battery and coils of wire combined to produce different effects. Iron and steel can also be magnetized by an electromagnet and stay magnetized for a long period of time. Materials A breadboard red and black alligator clip 0.9 m (3 ft) of 22-gauge magnet wire push-button momentary switch A x cm (6 x 6 in) piece of cardboard - cm (2 in) common nail 2-6 mm zinc washers Scissors 2 small paper clips 2 loose staples sandpaper A multimeter Group power supply 8

2 Experiment D Method. Cut a section from the piece of cardboard to 4 x 3 cm (. x in). 2. Roll the 3-cm (-in) side tightly around the nail. 3. Slide a washer over each end to points about 0.3 cm (0.2 in) from each end. 4. Cut a 0.9 m (3 ft) piece of 22-gauge magnet wire with scissors.. Place the sandpaper on the desk and sand the varnish off the two ends of magnet wire to about 3 cm ( in) up. Make sure to get the varnish off so that you can see the copper color of the bare wire under the varnish. 6. Leaving a cm (2 in) lead and starting at one end beside a washer, wrap the wire around the form, moving toward the other end with each turn. 7. Now go backward and wrap the wire on top of the windings you just completed until you return to the place you started. Approximately cm (2 in) of wire should be left so that you now have two 2-in leads. 8. The magnetic field produced around a wire and strengthened by coiling the wire around the coil form produces a force on the steel nail, which is a ferrous iron-based magnetic material. This force attracts the nail and moves it through the coil. 9. Place the paper clip contacts on the breadboard as shown. 0. Place the momentary switch as shown.. Push the two ends of coil wire into the correct places on the breadboard and bend them up so that they stand by themselves as shown. 2. Connect the group power supply to the positive and negative terminals of the breadboard with alligator clips. 3. Place the nail point-first into one end of the cardboard sleeve so that the point is about halfway in. 4. Push the momentary switch (a momentary switch is one that only makes a contact when you hold it down). The nail should quickly slide into the sleeve you have now made a solenoid switch.. This switch is used in cars to turn on the electric starter motor switch without having to run the heavy current-carrying wires all the way back to the car s ignition switch. The solenoid features a lighter current-carrying wire. 6. Using scissors, cut another piece of cardboard 8 x 3 cm (3 x in) and fold the ends down.3 cm (0. in). Coil form before winding 9

3 Experiment D 7. Push the nail all the way into the solenoid and place the cardboard cradle you have just made under the point. 8. Place two staples on the cardboard cradle under the point, about.3 cm (0. in) below it. 9. Now press the momentary switch. The staples should be attracted to the electromagnet you created. Experiment with the best height by bending the coil up or down until the staples are only attracted when the magnet is turned on.. Remove the nail and try to pick up a staple with just the nail. 2. You have just magnetized the nail by using the electromagnet, which aligned the tiny magnetic parts of the steel (called dipoles) and made the nail magnetic. This effect is called residual magnetism and is how magnetic recording tape works. VCR and cassette tapes store and erase information by being magnetized. 22. Practice using the multimeter to measure voltage or resistance across the coil. Because a coil is really just wire and is almost a short circuit, the current measurement should be avoided because it is beyond the range of the multimeter and could damage it. 23. The staples are attracted to the nail because of residual magnetism, the magnetism left in the nail after it has been subjected to a magnetic field. 60

4 Student Handout Layout Sheet D Solenoid Switch Paper clip with red alligator clip to group power supply 6 Paper clip with black alligator clip to group power supply Connections Connect: Switch a and strip Coil e - strip 6

5 Student Handout Layout Sheet D Solenoid Switch 6 3 0(-) Pictorial Drawing coil switch Group Power Supply 6 V DC Schematic Drawing 6 V DC 62