Physics for the Inquiring Mind (PHYS 105)               Fall 2005 Exercises for Thursday, October 13. [1] On Friday, you used your multimeter to measure current.  In this configuration, it is called an Ammeter (because current is measured in Amps).  Today you will be using it to measure resistance.  When we do this, we call it an Ohmmeter (because resistance is measured in Ohms). When using the multimeter to measure resistance, you need to have one lead in the COM hole and the other in the VÙmA hole.  For today, you will want to set the dial to 200 in the Ù section (the six-o-clock position).  The symbol Ù is the abbreviation for the word “Ohms”. [2] Grab a box of equipment for your group.  In your box there is an envelope containing nine resistors.  Three of them are 10 Ohm resistors, three are 27 Ohm, and three are 47 Ohm.  Use your multimeter on the resistance scale to determine which resistors are which.  As you do this, record the actual resistance of each resistor (they should be close to 10, 27, and 47, but they may vary a bit).  You will probably notice that the colored bands on a resistor indicate its resistance.  Each color corresponds to a certain digit - make a note of the colors so that you can determine which color goes with which digit. [3] Connect two of your 10 Ohm resistors in series and measure the total resistance of the combination.  Now connect three of the 10 Ohms in series and measure their total resistance. [4] Using what you have learned from step [3], predict what the total resistance will be when (a) you hook a 10 Ohm resistor in series with a 27 Ohm resistor, and (b) when you hook two 27 Ohm resistors in series with a 47 Ohm resistor. [5] Check your predictions from part [4] above. [6] State a rule for determining the total resistance of a set of resistors connected in series. [7] Connect two of your 27 Ohm resistors in parallel and measure their total resistance.  Predict the total resistance that two 47 Ohm resistors connected in parallel will have.  Check your prediction. [8] Connect three of your 10 Ohm resistors in parallel and measure their total resistance.  Predict the total resistance that three 27 Ohm resistors connected in parallel will have.  Check your prediction. [9] Measure the total resistance when a 10 Ohm resistor is connected in parallel with a 27 Ohm resistor.  Predict the total resistance when a 27 Ohm resistor is connected in parallel with a 47 Ohm resistor.  Check your prediction. [10] State a rule for determining the total resistance of a set of resistors connected in parallel. [11] See if you can create an arrangement of resistors that has a total resistance of 15 Ohms. [12] As homework for Friday, October 14, read pages 418-419, 422, the bottom of 423, and 424.  Do Exercise 5.6 on p. 425.