TO THE STUDENT

Welcome to this science exercise. We hope that you will find it interesting and worthwhile. Carefully read through these directions and the directions on the next page before you begin to work.

You may be part of a group for the first part of this exercise. Each group should carry out the experiment and collect the data together, but each student must record the data in his or her own booklet. Be sure to record the data exactly as you see it. After the data has been collected, each student should answer the questions independently.

After you have finished your experiment and have recorded all of the data, you will be asked to answer some questions about the experiment and the data you recorded. Your answers must be written in this test booklet in the space provided. Make sure that you understand each question before you begin to write. At any time while you are writing your answers, you may look back to the directions for the experiment and the data you collected. Be sure that your answers are written as clearly and neatly as possible.

Before you turn the page, read the list of materials given below and check to make sure that your group has everything listed.

When voltage is applied across a conducting wire, we may think of the electrons as being jostled against each other. This motion causes the wire to heat up. This is how toasters, electric heaters, and hair dryers work. Some wires are better radiators of heat than others. This event is designed to investigate the relationship between different types of wires and their ability to radiate heat.

Assume that you have a space heater that operates on a 6 volt battery. You discover that a wire in the heater is broken. The following types of wires are available at the store.

• 32-gauge copper
• 36-gauge copper
• 32-gauge steel
• 32-gauge nichrome

You will now conduct an experiment to find out how well each wire radiates heat. You will hang a wire with a weight attached over a crayon and then run electrical current through it. The time it takes the wire to cut through the crayon will indicate how well that wire radiates heat.

• Construct the circuit shown in the diagram below.
  
  
• Remove the paper from the crayon.

• Hang the wire 1 cm from the end of the crayon. It is crucial that there be a complete pathway for the flow of electricity, as indicated in the diagram.

• Hang the weight from the clips. Use the string, not the wire.

• Do not allow the pull of the weight to draw the two clips together. Make sure that the insulating covers are over the clips.

• Do not close the knife switch or complete the circuit until you are ready to start timing.

• Close the knife switch to make the connection complete and start the stopwatch at the same time. After the current begins to flow through the wire, make sure that the wires do not touch, or your circuit will be shorted out. Also, do not pull down on or influence mass in any way.

• As soon as the wire cuts all the way through the crayon and the weight drops, STOP THE STOPWATCH, THEN OPEN THE KNIFE SWITCH SO ELECTRICITY STOPS FLOWIN THROUGH THE CIRCUIT. Record the time in Table 1. Repeat this procedure for the rest of the wires.

• Give each wire no longer than 5 minutes to cut through the crayon. If it has not cut completely through in 5 minutes, record how far the wire has cut through the crayon in that time.

• After you are finished clean up your work area.

Additional observations:

1. Explain your experimental results. Include in your answer a discussion of how the gauge of a wire and type of wire affect the amount of heat radiated.
   
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2. Which of the wires would you use to repair your space heater? Be sure to justify your answer using the data you collected.
   
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