| Physics for the Inquiring Mind [Phys 105] |
| Spring 2005 |
[1] Pull out the (possibly quite vintage!) Decade Resistance Box in your kit. This box is handy because it has a variable resistance. That is, you may set its resistance to be whatever you desire.
There are three different scales on the box that, in combination, determine the resistance of the box in Ohms. That's right, resistance is measured in Ohms. Set the resistance of your box to 50 Ohms. If you have any questions about how to do this, please ask!
[2] Set up the circuit below involving your battery pack, one ammeter, and the decade resistance box. Remember, your resistance box should be set to 50 Ohms before you hook this circuit up.
After you have gotten a non-zero reading on your ammeter, you are free to change the dials of the resistance box. But….
While the box is hooked up in your circuit, make sure that it never gets set below 1 Ohm.
[3] How does the current flowing through the ammeter change as you change the resistance of the decade box? Do high resistances give you large currents or small currents?
[4] Now hook up the circuit depicted below. The zig-zag symbol represents one of the resistors in your kit that is marked with a Blue Gray Black Gold color code.
[5] If the resistance box happened to have the same resistance as your Blue Gray Black Gold resistor, how would the readings on the ammeters in Part [4] compare?
Use this idea to determine the resistance of your Blue Gray Black Gold resistor. When you think you have it, show John.
[6] Now replace the resistor in your circuit from Part [4] above with a light bulb. Use this new circuit to determine the resistance of your light bulb.
[7] Finally, replace the light bulb by two Blue Gray Black Gold resistors in series, so that your total circuit looks like:
Use this circuit to determine the total resistance of your two resistors in series.
[8] As Homework for Thursday, February 24 {don't come to class on the 22nd!}, do Exercise 4.9 on p. 413, Exercise 4.10 on p. 414, and Exercise 4.11 on p. 415.