Three identical light bulbs are connected in the circuit shown above. The switch

Question

Three identical light bulbs are connected in the circuit shown above. The switch S is initially in the open position and then is closed at time t. (a) Describe any changes that occur in the current through each bulb when the switch is closed. Justify your answers, (b) Describe any changes that occur in the brightness of each bulb when the switch is closed. Justify your answers. (c) When the switch is closed, does the power output of the battery increase, decrease, or remain the same? Justify your answer. (d) When the switch is closed, the current in Bulb 1 changes. Explain why this change in current does not violate the law of conservation of charge.

Explanation / Answer

a)

as the switch is closed , the overall resistance of the circuit decreases since abulb in parallel has been added. This decrease in the resistance increases the current from the battery

since Bulb 1 is in series with the battery , current in bulb1 increases.

as the bulb 2 becomes connected with the circuit , the current in bulb 2 also increases as compared to when no current was flowing .

The current in bulb 3 decreases since the current gets divided between bulb 2 and bulb 3

b)

Let the resistance of each bulb be "R"

Before the switch was closed , bulb 1 and bulb 3 were in series and their combination is gives the total resistance as

Rtotal = R13 = R + R = 2R

After the switch was closed , bulb 2 and bulb 3 becomes in parallel and total resistance of the circuit becomes

Rtotal = R + (R x R/R + R) = 1.5 R

hence the total resistance of the circuit decreases which in turn increases the total current coming from the battery

since the bulb1 is in series with the battery , the current in bulb1 increases and hence bulb 1 glows brighter

The bulb 2 starts glowing as the switch is closed.

the bulb 3 becomes dimmer as the current in it is smaller as compared to when the switch was not closed.

c)

as the switch is closed , the overall resistance of the circuit decreases since abulb in parallel has been added. This decrease in the resistance increases the current from the battery.

Power output is given as

P = current x Voltage

since the current increases as the switch is closed, hence the power output increases too.

d)

bulb 1 is in series with the battery . the current flowing in the bulb is same as the current coming from battery. the current that increased is coming from the battery , hence it does not voilate the conservation of charge rule

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.