3 V=I·R VOLTS= AMPERES X RESISTANCE What do the words meanVolts- the amount of energy that the charged particles have.Amperes (Amps)- the amount of charged particles that pass a given point in a given time.Resistance- the amount of difficulty the charged particles encounter in their movement. Many things can cause resistance in a circuit, including lengthing the wire, decreasing the diameter or the wire, or adding appliances to the circuit.
4 Calculating V= I X R in Parallel Circuits Each parallel on the circuit can be figured using V=IR. To find the total amps, volts, or resistance in the circuit, figure each parallel individually and add them together.Amps will be highest where resistance is lowest as shown in the see saw below.VoltsAmpsResistanceUse this information to predict the results of the following situations:1. I have a parallel circuit with two small bulbs and a large appliance. Which parallel is receiving the least amps and why?2. My battery is producing 10 volts. I am about to put a light bulb of 10 ohms resistance on the circuit but I need to know how many amps it will draw. Can you help? (V=IR, R=V/I, I=V/R)
5 Calculating V= I X R in Series Circuits 1. Finding Amps- Add up total resistance on the line and use V=IR to find the amount of amps on the line.2. Finding Volt for each resistance- Once you have the amount of amps, use V=IR to find the voltage drop for each individual resistance.Calculate the number of amps in this circuit. The battery is producing 10 volts and each bulb is 10 ohms of resistanceCalculate the voltage drop for each bulb (it will be the same for all three.).3333 ampsvolts
6 The following picture shows a bulb that is a 10 ohm resistor and a battery that is 10 volts. Can you figure out how many amps it is drawing from the battery? Click for an answerV= IR, so with 10 volts, unknown amps, and 10 ohms of resistance, we can figure-V/R= I V/10ohms =1 ampere (the voltage drop isn’t exactly 10 but close enough)Predict the # of amps for one more light in parallel. Click for help.O.K. Here’s a hint. Use V= IR to figure out the amps for each parallel circuit. Now think of the different circuits as different hallways for students (amps) to exit a building (the battery). If you know how many students are in each hallway, and how many hallways there are, you can calculate the total # of students.Did your math work out? Do you understand?Look at the last picture- Do you understand why there are 3 amps being drawn from the battery?Then predict for another resistor added of 200 ohms…
7 Compared toAdding another 200 ohm resistor barely changed the number of amps. Calculate the number of amps added if the resistance added is a wire with resistance of ohms. Click for the answer.
8 Amps vs. Resistance Analogy The reason why the number of amps increases so much is because the wire offered very little resistance. If the volt is constant, the amount of resistance and amps will contrast each other. If the resistance is high, the amps will be low, but if the resistance is low, the amps will be high.Use the analogy of students walking in hallways to remember. The square on the left represents a gym where the entire school has just gathered for an assembly. Students are now exiting to their rooms. Notice that because the hallways aren’t very wide, it is very crowded and students are restricted in their movement. Click once. Now describe on your student sheet what you think will happen, especially in the high resistance hallways. Relate to electricity.High resistance hallwaysIce-cream shop-Just Opened!Free ice creamfor the next5 minutes!Low resistance hallwayNew extra-wide hallway just built!
9 Compare each of the three pictures with the picture before it and below it. The circled A on the wire shows where the amount of amps was measured. Discuss patterns.Now recall the addition of a low resistance wire. What would this wire be called? What might happen to the wire with that much current? What device do we have in our house to protect against this? Would we place the device at point A, B, C, or D. Why?ABCD