Three bulbs A circuit is made of two 1.4 volt batteries and three light bulbs as
ID: 2261521 • Letter: T
Question
Three bulbs
A circuit is made of two 1.4 volt batteries and three light bulbs as shown in the figure. When the switch is closed and the bulbs are glowing, bulb 1 has a resistance of 5 ohms, bulb 2 has a resistance of 45 ohms, bulb 3 has a resistance of 26ohms, and the copper connecting wires have negligible resistance. You can also neglect the internal resistance of the batteries.
Explanation / Answer
A circuit is made of two 1.6 volt batteries and three light bulbs as shown in the figure. When the switch is closed and the bulbs are glowing, bulb 1 has a resistance of 10 ohms, bulb 2 has a resistance of 38 ohms, bulb 3 has a resistance of 33 ohms, and the copper connecting wires have negligible resistance. You can also neglect the internal resistance of the batteries.
a) With the switch open, indicate the approximate surface charge on the circuit diagram.(Do this on paper. Your instructor may ask you to turn in this work.) Refer to your diagram to decide which of the following statements about the circuit (with the switch open) are true:
The surface charge on the wire at location B is positive. is TRUE but the charge is bound, you cannot transfer it to electroscope
There is a large gradient of surface charge between locations M and L. FALSE
The electric field in the filament of bulb 3 is zero. TRUE 3.6/(distance in m between B and C) V/m
There is no excess charge on the surface of the wire at location C TRUE (negative charge), but the charge is bound, you cannot transfer it to electroscope
The electric field in the air between locations B and C is zero. FALSE
(b) With the switch open, find these potential differences:
VB - VC = 3.6 V
VD - VK = 0 V
(c) After the switch is closed and the steady state is established, the currents through bulbs 1, 2, and 3 are I1, I2, and I3 respectively. Which of the following equations are correct loop or node equations for this steady state circuit?
I2 = I3 FALSE as r2 and r3 are not equal
-I1*(10 )-I2*(38 ) + I3*(33 ) = 0 FALSE
+3.2V + -I1*(10 ) + I3*(10 ) = 0 FALSE
I1 = I2 + I3 TRUE
+3.2V + -I1*(10 ) + -I2*(38 ) = 0 FALSE
-I2*(38 ) + I3*(33 ) = 0 TRUE
(d) In the steady state (switch closed), which of these are correct?
VC - VF = +I2*(38 ) TRUE
VC - VF = 0 FALSE
VL - VA = -3.2V + I1*(10 ) TRUE
VC - VF = +I1*(10 ) FALSE
VC - VF = +I3*(33 ) TRUE
(f) Now find the unknown currents, to the nearest milliampere.
I1 = 115 mA
I2 = 53 mA
I3 = 62 mA
(g) How many electrons leave the battery at location N every second?
723014256619144603 electrons/s
(i) What is the numerical value of the power delivered by the batteries?
P = 0.3702 W
(j) The tungsten filament in the 38 ohm bulb is 9 mm long and has a cross-sectional area of 2 10-10 m2. What is the magnitude of the electric field inside this metal filament?
|| = 227 V/m
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