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Transcript
Objective: To calculate the total resistance in series and parallel circuits in order to apply Ohm’s Law. Energy Note: How do circuits differ from each other?? Drill: 1. Get a new lab from the SET. 2. Form groups. 3. Each group needs a materials tote and BOTH circuit boards. 4. Compare your homework diagrams. 5. Wait quietly for directions. GTE-8B on e Objective: To calculate the total resistance in series and parallel circuits in order to apply Ohm’s Law. Energy Note: How is the total resistance in a circuit calculated? Drill: 1. Open your Log Book. 2. Come up with an analogy for current, voltage, and resistance. Thin about roads, pipes, rivers, etc… GTE-8B on e Activity 1: Setting the Stage If the resistance in a circuit is 12 ohms, and the voltage is 120 volts, what is the current? Show all work using proper form. Current = Voltage ÷ Resistance Current = 120V ÷ 12Ω Current = 10A Are all circuits this simple? Explain your thoughts. GTE-8B on e Resistance in a Series Circuit The resistance in a series circuit is equal to the sum of the individual resistors in the circuit. Why? Every electron must pass through each resistor. GTE-8B on e Example: If there are two 3 ohm resistors and one 4 ohm resistor in a series circuit, the total resistance equals _____ ohms. 10 Ohms Practice Problem: If a series circuit is powered by a 20 volt battery and there are two bulbs on the circuit, each with a resistance of 4 ohms, what is the current? (Calculate the total resistance first and then apply Ohm’s Law.) GTE-8B on e Resistance = 4Ω + 4Ω = 8Ω Current = Voltage ÷ Resistance Current = 20 V ÷ 8Ω Current = 2.5A GTE-8B on e Activity 3: Resistance in a Parallel Circuit In a parallel circuit, what happens to the resistance when branches are added? The total resistance decreases. GTE-8B on e Resistance in a Parallel Circuit The reciprocal of the total resistance in a parallel circuit is equal to the sum of the reciprocals individual resistors in the circuit. This is because all of the current does not have to go through each resistor. GTE-8B on e Practice Problem: If a parallel circuit is powered by a 20 volt battery and there are two bulbs on the circuit, each with a resistance of 4 ohms, what is the current? (Calculate the total resistance first and then apply Ohm’s Law.) GTE-8B on e 1 1 1 Resistance = 4Ω + 4Ω = 2 4Ω Resistance = 2Ω (reciprocal of 2/4) Current = Voltage ÷ Resistance Current = 20 V ÷ 2Ω Current = 10A GTE-8B on e Look at the answers to the two practice problems. What concept(s) is/are illustrated by the solutions? 1. When the same resistors are wired in series the total resistance is greater than that of the same resistors wired in parallel. 2. Therefore, the current in the parallel circuit is greater. GTE-8B on e Class Practice HOMEWORK: Self Practice GTE-8B on e