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Concept Questions with Answers 8.02 W10D2. W10D2 DC Circuits. Today ’ s Reading Assignment W10D2 DC Circuits & Kirchhoff ’ s Loop Rules Course Notes: Sections 7.1-7.5. 2. Concept Q: Resistors In Parallel. Suppose that . Then the equivalent resistance 2.
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W10D2DC Circuits Today’s Reading Assignment W10D2 DC Circuits & Kirchhoff’s Loop Rules Course Notes: Sections 7.1-7.5 2
Concept Q: Resistors In Parallel • Suppose that . Then the equivalent resistance • 2. • 3. • 4.
Concept Q: Resistors In Parallel Answer. When Then the equivalent resistance is the smaller resistance. This is an important circuit design principle.
Concept Question: Bulbs & Batteries An ideal battery is hooked to a light bulb with wires. A second identical light bulb is connected in parallel to the first light bulb. After the second light bulb is connected, the current from the battery compared to when only one bulb was connected. • Is Higher • Is Lower • Is The Same • Don’t know
Concept Question Answer: Bulbs & Batteries Answer: 1. More current flows from the battery There are several ways to see this: (A) The equivalent resistance of the two light bulbs in parallel is half that of one of the bulbs, and since the resistance is lower the current is higher, for a given voltage. (B) The battery must keep two resistances at the same potential I doubles.
Concept Question: Bulbs & Batteries An ideal battery is hooked to a light bulb with wires. A second identical light bulb is connected in series with the first light bulb. After the second light bulb is connected, the current from the battery compared to when only one bulb was connected. • Is Higher • Is Lower • Is The Same
Concept Question Answer: Bulbs & Batteries Answer: 2. Less current flows from the battery The equivalent resistance of the two light bulbs in series is twice that of one of the bulbs, and since the resistance is higher the current is lower, for the given voltage.
Concept Question: Power An ideal battery is hooked to a light bulb with wires. A second identical light bulb is connected in parallel to the first light bulb. After the second light bulb is connected, the power output from the battery (compared to when only one bulb was connected) • Is four times higher • Is twice as high • Is the same • Is half as much • Is ¼ as much
Concept Question Answer: Power The current from the battery must double (it must raise two light bulbs to the same voltage difference) and Answer: 2. Is twice as high
Concept Question: Power An ideal battery is hooked to a light bulb with wires. A second identical light bulb is connected in series with the first light bulb. After the second light bulb is connected, the light (power) from the first bulb (compared to when only one bulb was connected) • Is four times higher • Is twice as high • Is the same • Is half as much • Is ¼ as much
Concept Question Answer: Power R doubles current is cut in half. So power delivered by the battery is half what it was. But that power is further divided between two bulbs now. Answer: 5. Is 1/4 as bright
Concept Question: Measuring Current If R1 > R2, compare the currents measured by the three ammeters: • A1 > A2 > A3 • A2 > A1 > A3 • A3 > A1 > A2 • A3 > A2 > A1 • A3 > A1 = A2 • None of the above • Not enough information is given.
Concept Question Answer: Measuring Current Answer: 4. A3 > A2 > A1 The total current must add to the two individual currents, so A3 must be largest. Most current prefers to go through the smaller resistor so A2 > A1 .