Direct Current Circuits And Resistance

Purpose:  We introduce direct current circuits. We also introduce the idea of resistance, how to orient them and how to measure this orientation.

Circuit 1

Professor Mason begins by demonstrating two kinds of circuits with light bulbs attached. The first is a circuit with a switch at the center wire and the center wire also has a light bulb. The other two light bulbs are are a part of a circuit of one loop when the switch is open and these light bulbs are hooked in series as well as the batteries. The light bulbs in series are on due to the power supplied from the battery. The question is, if we close the switch, will the light at the center turn on. We find that it does not because the potential along the center wire is zero and with no potential, no power to light the bulb.

Circuit 2

In the second circuit, we have the two light bulbs connected in series when the switch is open. The question is, what happens when the switch is closed, introducing a new battery? We find out that the batteries do not change their brightness. This is because the potential drop remains the same, therefore, the power supplied to the bulbs do not change.

Summary Of the Circuits

Our board summarizes what occurred with the light bulbs when we closed the switch, which is no change.

The Introduction Of Resistors

On the top left corner of the board, we make a list of the ways we can configure the light bulbs and the batteries to make the lights dim or bright. We conclude that the brightness is dependent on the voltage and the current. We, then, introduce resistors in series connected to two power supplies in series. We do this to see how the resistance adds up in series. When we measure the resistance using the multimeter, we find the total resistance of the resistors in series is just the sum of the resistors.

Resistance In Parallel

Next, we connect the two resistors in parallel and measure the total resistance. The inverse of the total resistance turns out to be the inverse sum of the resistors.

In the lab manual, we document all of the voltages and current across the two orientations of resistance done previously. We find that the current splits into two smaller current after the first junction and the sum of the two smaller currents is equal to the initial current. If there are no junctions, the current is that same throughout and this current is dependent on the amount of resistance in the circuit.

Reading The Resistance Of Resistors

On the left hand side of the board, there are a bunch of resistors. These resistor have color markings on them so that a person can determine the resistance. The way to do this is to find the initial color and final color. The final color will determine the tolerance of the resistance while the color next to it is called the multiplier. This multiplier just multiplies the number received by the initial colors. The initial colors indicate single digits that determine the magnitude of the resistance and this is multiplied by the multiplier if it is larger by 10n times the digits found.

Finding The Equivalent Resistance

To get the hang of finding the equivalent resistance, we start off by finding equivalent resistance of a simple orientation of resistors.

In this image, the resistors are oriented more randomly. The key here is to find equivalent resistance of parts of the circuit, until it looks like a simple parallel or series orientation. For example, we start by looking at the top left parallel wires. We know how to add parallel resistors but we can only do it if the is one representation of resistance on each wire. We get this single representation by first finding the single representation of the two resistors in series, then, we find the equivalent resistance of the parallel wires. We keep doing this, little by little, until we had a single resistance that represents all of the resistors.

Conclusion:  We found that the key to a light bulbs brightness depends on the potential difference as well as the current, which is the power. This is proved by the first two circuits, especially the first. Our group believed the the middle bulb would turn on because flipping on the switch would introduce current. But the potential difference turned out to be zero and this causes no power to be supplied. We found out how to read the resistance of a typical resistor. These values are determined using colored strips. We, also, found a way for getting the equivalent resistance of any orientation. This is important because it allows us to get the desired resistance using a multitude of fix values of resistors.