Introduction to series circuits Welcome Back! We hope you had a restful spring break. Seed Question: What is a circuit? What are the 5 basic parts of a circuit?

Series circuits only have one possible pathway for electrons. Ask students to draw this circuit as a schematic diagram, press to animate and bring in the schematic….Series circuits can have multip0le resistors and multiple batteries. These resistors (light bulbs) are connected in series because the electrons in the circuit can still only go in one path.

Ammeter and Voltmeter. Ammeters measure current and are connected in SERIES. This means that they are a part of the loop itself. Voltmeters are not connected in the main loop, they are on a separate branch. Voltage can only be measure across the battery or across a resistor but current can be measured anywhere. Draw some pictures on the board to demonstrate what this means. In addition to the 5 basic parts that we have already discussed, there are two very important measurement devices used for circuit labs.

Series circuits obey some specific rules regarding resistance, voltage, and current. Today in the virtual lab you will try to figure out what these rules are. Each group will do a different configuration of the Phet and present their findings on a white board to the rest of the class. As the finding are shared we can develop the rules in the remainder of the power point. This is meant to be discovery.

As you add resistors in series, the equivalent (total) resistance increases. 𝑅 𝑇 = 𝑅 1 + 𝑅 2 + 𝑅 3 …………… The more resistors you add, the more resistance there is. Click through the examples and ask students to calculate equivalent resistance. Use the first picture as an example to explain that the total resistance in a series circuit is simply added up. Circuit #1 18Ω Circuit #2 232 Ω Circuit #3 34Ω

You can also look at total equivalency (aka equivalent resistance) as simplifying the circuit to the simplest form.

Current is the same at all locations in the circuit. 𝐼 𝑇 = 𝐼 1 = 𝐼 2 = 𝐼 3 = 𝐼 4 The total amount of current in the system never changes. If you measured using an ammeter at positions 1, 2, 3, &4 they would all give the same measurement.

As you add resistors in series the total amount of current decreases. 𝐼= 𝑉 𝑅 As you add resistors in series the total amount of current decreases. 1. 3. 2. Which will have the smallest current? What will the currents be EXACTLY (using Ohm’s Law)? Circuit #1 = 9/18 = 0.5 A Circuit #2 = 12/34 = 0.35 A Circuit #3 = 25/232 = 0.11 A

The voltage gained across the battery is equal to the sum of the voltage drops across the resistors. 𝑉 𝑇 = 𝑉 1 + 𝑉 2 + 𝑉 3 ……… If all the resistors have the same amount of resistance then the voltage drop across each is the same. So if this battery supplies 3 volts, there is 1 volt dropped across each resistor so that there is NO voltage left. If the battery provides 12 V then then 4 volts would drop across each. If the resistors do NOT have the same resistance, the voltage drop across each is not identical, the larger the resistor the more voltage is dropped across it. There are four total examples on this slide.

Try to figure out voltage drop on your own. Two 5Ω resistors are connected in series to a 12V battery. Calculate the voltage drop across each resistor. A 5Ω and 10Ω resistor are connected in series to a 15V power supply. Calculate the voltage drop across each resistor. This slide is to kind of get them to see that they need an organized method of solving for circuits. This will segue to discussing how to solve problems.

Solving series circuits requires organization. Resistor R I V 1   2 Total 5 Ω 0.5 A 2.5 V 1 Ω 0.5 A 0.5 V 6 Ω 0.5 A 3 V Given enough information there are a lot of things you can find out about a circuit, but it is easiest to process the information when you use a chart to record the things you know. Lets fill in what we know from just looking at the diagram. What do we know about the resistors? (click to animate). What does the battery tell us? (click to animate) Now lets figure out the total resistance. (click to animate) Using the total resistance and total voltage we can find the total current. (click to animate) What do we know about current in a series circuit? (it’s the same everywhere)(click to animate) Lastly calculate the voltage drop across each resistor using the information across each row. To check your work the voltage dropped across the resistors should add up to the total voltage. Discuss what each of the meters would read.

Try to solve a series circuit on your own. Resistor R I V 1   2 Total 3 Ω 2 Ω 2 A 4 V 3 Ω 2 A 6 V 10 V 2 Ω 5 Ω 2 A 10 V What do we do first? (List what we know from the image.) Next? (Sum the resistors.) Next? (Calculate the current and remember it is the same everywhere so that column should have all the same #) Next? (Figure out voltage drop across each resistor) What would each meter read?

Just ONE more! Resistor R I V 1 2 Total 150 Ω 0.013 A 2 V 300 Ω   2 Total 150 Ω 0.013 A 2 V 300 Ω 0.013 A 4 V 450 Ω 0.013 A 6 V