1. Concept Questions with Answers 8.02 W10D2

2. Week 04, Day 2
W10D2 DC Circuits
Today’s Reading Assignment W10D2 DC Circuits & Kirchhoff’s Loop Rules Course Notes: Sections 2
Class 09 2

3. Concept Q: Resistors In Parallel
Suppose that Then the equivalent resistance 2. 3. 4.
Class 12

4. Concept Q: Resistors In Parallel
Answer. When
Then the equivalent resistance is the smaller resistance. This is an important circuit design principle.
Class 12

5. 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
Class 12

6. 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.
Class 12

7. 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
Class 12

8. 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.
Class 12

9. 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
Class 14

10. Concept Question Answer: Power
Answer: 2. Is twice as high
The current from the battery must double (it must raise two light bulbs to the same voltage difference) and
Class 14

11. 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
Class 14

12. Concept Question Answer: Power
Answer: 5. Is 1/4 as bright
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.
Class 14

13. 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.
Class 14

14. 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 .
Class 14