Consider the circuit below, consisting of a 1.5 V battery, a switch and four ide
ID: 1624085 • Letter: C
Question
Consider the circuit below, consisting of a 1.5 V battery, a switch and four identical bulbs, labelled A - D. The switch is initially closed. Rank the brightness of all four bulbs in the circuit. If any of the bulbs have equal brightness, state that explicitly. Explain your reasoning. (Remember to use the finger tracing method.) Now the switch is open (as shown). Does the brightness of bulb B increase, decrease, or remain the same? Explain. Does the brightness of bulb A increase, decrease, or remain the same? Explain. A voltmeter is now placed across bulb C. What will the voltmeter read? Explain.Explanation / Answer
a.) If we name arms with A,B and that with C and D as arms 1,2 and 3 respectively , then all 3 arms have equal voltages and equal current. As brightness depends upon power i.e V×I , bulbs A and B will have equal brightness as they are getting same current and voltage. But in arm 3 voltage gets divided between bulbs C and D, their brightness wil be lesser than that of A and B. But C and D will have equal brightness.
b.) On opening the switch brightness of B will decrease and becomes zero as current in that arm will be zero.
c.) Brightness of A will increase because earlier current was divided between 3 arms. Now on opening the switch it is divided between 2 arms, hence it increases :.V×I also increases.
d.) As the bulbs are identical, they will have equal resistance. Now voltage across arm3 is 1.5 V, it will get divided equally between C and D, hence voltmeter across C will read 0.75volt.