Can someone please help me with number 3 and 4. Please explain. Thanks Bulbs A,
ID: 2278144 • Letter: C
Question
Can someone please help me with number 3 and 4. Please explain. Thanks
Bulbs A, B and C in the circuit diagram to the right are identical. Rank in order, from most to least, the brightness of the three bulbs. Explain your reasoning. Suppose an ideal wire (with negligible resistance) is connected between points 1 and 2. What happens to each bulb? Does it get brighter, dimmer, or go out completely? Explain your reasoning for each bulb. Use Kirchhoff's rules to find the current in each of the three resistors in the circuit shown at right. Also, calculate the voltage drop across all three resistors.Explanation / Answer
3)
a) The brightest is bulb A, and the other two have the same brightness as each other. The reason is that each light bulb is acting like a resistor. The total current going through A is the same as the total going through B and C combined. Since the power is proportional to the square of the current, and since B and C split the current equally between them, then they have 1/4 the power of A, and so A must be brighter than the other two.
b) Bulb A gets brighter, the other two bulbs become extremely dim. The reason is that the wire acts as another resistor in parallel with B and C. Because the wire has a much smaller resistance, almost all of the current that used to go through B and C will now go through the wire instead. As before, since the power is proportional to the square of the current, this much lower current means much dimmer bulbs. This also means that the overall resistance in the circuit is lower, while the voltage is the same, so the current increases. Which is why A gets brighter.