Physics Lab
CUP OF SPEAKER

Purpose: To understand how a speaker generates sound waves.

Materials (per group):

1 personal stereo 1 paper cup (4 oz. to 10 oz)

1 small bar magnet masking tape

2 ice cream sticks 1 3 x 5 index card

scissors sand paper

6 meters of thin enameled wire 1 monaural transistor radio ear plug

Procedures:

1. Turn the cup upside down. Neatly tape the magnet so that it sticks up from the center of the cup's bottom.

2. Tape the ice cream sticks firmly on the outside of the cup as shown.

3. Cut a 5-centimeter strip from the index card. Roll and tape the strip into a tube with about a 2-centimeter diameter. The tube will have a thickness of about three card "layers." Make sure the tube fits easily around the magnet and can move freely up and down over it. 

4. Cut a tiny slit in one end of the tube. Run the wire through the slit and wrap it around the tube about fifty times. Leave a long end of wire sticking through the slit for your final connection. Don't overlap the wire as you loop it. When you have a nice neat coil, place a small piece of tape over the loose end but again leave a long end of wire for your final connection.

5. Sand your loose ends well to remove any oxide or coating that may be on them.

6. Slide your tube-coil down over the magnets on your cup and tape it loosely to the ice cream sticks. It should not touch the bottom of the cup nor the sides of the magnets. It should not be too high above the cup bottom either. The coil has to be able to vibrate.

7. Plug your monaural transistor into you walkman and then connect the free ends to the free ends of your coil of wire. Do not let the wire cross and touch. Turn on your radio and place the open end of the cup to your ear. You should be able to hear your favorite radio station. If not...try adjusting the tube and checking your connections. The teacher must actually hear your speaker work and check off your paper.

Questions

1. Current in a wire makes a magnetic field. What does the information have to do with your speaker? (Hint: what vibrates to
make the sounds from your radio)

2. What would happen if you didn't have the magnets taped to the cup?

3. Why do you need the cup?

4. How could you make your speaker louder?

Standard lab report is required.