Download WS 10.3 Solutions 10.3 Series and Parallel Circuits

WS 10.3: A Series of Parallels between Circuits and Chapstick Name: _____________________ 1. Consider the series circuit shown to the right. a. How does the current through the 35 Ω resistor compare to the current through the 15 Ω resistor? b. Use Ohm’s law to determine the voltage dropped across each resistor. Then add up the total voltage dropped across the three resistors, and box this value as ‘Vtotal’ below. c. What is the equivalent resistance of this circuit? Check your answer: Req = 75.0 Ω. d. Recall that the circuit can be thought of as a simple one‐battery‐one‐resistor circuit, with the one resistor being equal to the ‘Equivalent Resistor’. Draw this circuit, and determine the total voltage dropped across the equivalent resistor. What do you notice about this result? 25.0 
2. Consider the parallel circuit shown to the right. a. How does the voltage drop across the 15 Ω resistor compare to the 15.0 
voltage drop across the 45 Ω resistor? 12.0 V
45.0 
35.0 
b. Use Ohm’s Law to determine the current in each leg of the parallel portion of the circuit. Then add up the total amount of current coming through the 4 legs, and box this value a as ‘Itotal’ below. c. What is the equivalent resistance of this set of resistors? Check your answer: Req = 7.76 Ω, NOT 0.129 Ω! d. Recall that the circuit can be thought of as a simple one‐battery‐one‐resistor circuit, with the one resistor being equal to the ‘Equivalent Resistor’. Draw this circuit, and determine the total current in the circuit. What do you notice about this result? 3. Recall the key elements of the Chapstick Analogy from today’s class; fill in the blanks with these circuit words: voltage current resistors electrons a. Imagine running to the bathroom just before class begins, during the passing period. You leave from class, travel to the bathroom, then return to class in a big loop. Now imagine doing this over and over again: this is similar to the motion of ____________ through a circuit. This is sometimes referred to as ‘charge’. b. It’s not just you that is making this bathroom run – everyone in our class is going. If one person leaves the classroom every couple of seconds, then an observer in the hall could count how many physics students pass by every second. The faster you’re all able to move, the more students pass by per second. This amount of students moving by per second is like the ____________ in a circuit, the charge moving by per second. c. Unfortunately, when trying to get through the halls, you are frequently slowed down by clusters of freshmen. They don’t get PDA – they stand in bunches, smooching their little significant others with their tired out and chapped lips, oblivious to the flow of traffic. You must push through. These freshmen herds that slow you down are just like ____________ in a circuit. d. You’re an upper classman and it’s your duty to take care of these young Mustangs. Therefore, every time you leave class, Mr. G you a handful of Chapsticks. As you push through these herds of smooching freshmen, you throw Chapsticks at them. The more smooching freshmen are in a group, the more Chapsticks you throw at them. You must throw ALL of your Chapsticks by the time you get back to class, and every group will get some Chapsticks. When you get back to class, you will get more Chapsticks to throw on your next trip. The number of Chapsticks supplied by Mr. G are like the amount of ____________ supplied by a battery. Using the Chapstick analogy, explain how the three Series Rules apply to the circuit drawn below: 1. In series, Req = R1 + R2 + R3 2. In series, Itotal = I1 = I2 = I3 3. In series, Vtotal = ΔV1 + ΔV2 + ΔV3 Using the Chapstick analogy, explain how the three Parallel Rules apply to the circuit drawn below: 1. Modified version: In parallel, the total resistance is LESS than the sum of all the resistors 2. In parallel, Vtotal = ΔV1 = ΔV2 = V3 3. In parallel, Itotal = I1 + I2 + I3