Circuits: Resistors

Below, Professor Mason is holding up a circuit board that he created. There are three light bulbs and two sources of voltage. There is also one switch. He asked us what would happen if he were to close the switch.

This is our prediction. We predicted this because we thought if the switch was closed, the three bulbs would then have to share the voltage sources.

Professor Mason then presented us with another circuit board. There are two light bulbs and three batteries except one is separated by a switch. He asked us then what would happen if he closed the circuit.

This was our prediction with explanation.

This was the actual result. Because the batteries were placed in series, there was no potential change.

We were then introduced to these little resistors. This is the inside of a resistor because Professor Mason had cut one in half.

On a resistor, there are four colored bands a person would look at to determine the strength of a resistor. Though the first one is not of our concern at the moment. Each color represents a value from 1 through 10. The general equation used to calculate the strength is AB*10^C. A is the second color, B is the third and C is the last.

These are some resistors that were in the lab. Each one has a different set of colors.

We were then asked to calculate the strength of three different resistors and to calculate the percent difference.

Using a multimeter, we were able to calculate the actual of each resistor. The value on the mutlimeter was off even with the given number because of the first color on each resistor. That color represented the percent error in each one.

This is a resistor set up in series. With this set up, the strength of it went up.

This is a pair of resistors set up in parallel.

And it turns out that the parallel set up makes the strength weaker.

These relationships is defined in two equations. When resistors are in series, we merely add the resistors together: R = R_1 + R_2 + ... R_n. If the resistors are parallel, the total is the addition of the resistors inverted: R = 1 / (( 1 / R_1) + ( 1 / R_2) + ... ( 1 / R_n)).

This is the value of three resistors in parallel.

Another set of three resistors in parallel.

The method of calculating the resistors on a circuit is by evaluating the ones in series first, then parallel. So below, we calculated the series resistors first to be 200 ohms, then the parallel relationship to be 66.67 ohms and the total of the resistor circuitry to be 166.67 ohms.

However, due to the uncertainities in each one being added as well, we were not precise. The actual relationship was 149 ohms.

Another example of an actual reading of the same set up.

As an introduction to Kirchhoff's Law, we calculated the currents and voltage of a given set up of a circuit board that included resistors. Kirchhoff's Law has us calculate the different variables by determining which ones are in which loops.