Circuit lab

Current and Resistance - a lab!

In this lab, you will determine the relationship (if there is one) between electrical current and resistance.

At this point, you should have a hypothesis - including the graph you expect will represent the relationship between current and resistance (I vs. R).

1.  Set up the circuit depicted in the pictures below:

Two batteries in series with the "resistance box" and a meter set to measure current (in A - use the 20A setting and socket for the red wire).  Connections are made with alligator wires - wires with "alligator" clips on each end.

Have a separate meter set up to measure voltage.  To do this, the meter needs to be "in parallel" with the resistance box.  See the picture below.

2.  Change the resistance in small increments, starting at around 4 ohms.  Write down the following data:  resistance (in ohms), current (in A), and voltage (in V).  Take at least 20 trials.  If you get to a point where the current is staying the same (or reading zero), try switching the dial to the mA setting (and move the red wire to the mA socket as well).

3.  For homework, plot a graph of current (I) vs. resistance (R).

4.  A few questions will be forthcoming.

  

In the last picture, the yellow meter is measuring current - it is IN SERIES with the batteries and resistance box.  The red meter is measuring voltage - it is IN PARALLEL with the resistance.  You will notice that a student is holding the leads from the meter - you may need to do the same.