Physics 112 HW15
Due Monday, 26 October 2015
/4
VIR01. The circuit at left consists of two batteries (the
4.00 V
grey shaded areas) broken up into ideal EMF sources
with internal resistances, along with two resistors.
c 9.00 Ω
b 0.50 Ω
a) What is the voltage difference between points a
and d?
6.00 Ω
b) What is the terminal voltage across the 4 V
0.50 Ω
a
8.00 Ω
battery? (What is the voltage one would measure
across it when it is put in this circuit, or the
8.00 V
voltage between points b and c?)
c) A battery with EMF 10.30 V and internal resistance 0.50 Ω is inserted at point d
in such a way that its negative terminal (the box) is connected to the negative
terminal of the 8.0V battery. What is the terminal voltage across the 4 V battery
now?
VIR02.
kΩ.
a)
b)
c)
d)
Consider the circuit at right. The (non-ideal) voltmeter has a resistance of 900
Calculate the voltage the voltmeter reads (the voltage across resistor R) if
R = 10 Ω,
150 kΩ
R = 10 kΩ, and
R = 10 MΩ.
20V
Repeat parts a – c if the voltmeter is ideal (it has essentially (ideal)
infinite resistance).
Does the finite resistance of
voltmeters matter?
VIR03. Consider the circuit at right. Both voltmeters and the ammeter are ideal; the “r”
represents the internal resistance of the battery. The
switch is initially open, and the voltmeter V1 reads 10
r
R1
volts.
Vo
V1
a) What does ammeter A read?
R2
b) What does voltmeter V2 read?
c) What is the voltage of the battery’s ideal
voltage source?
The switch is now closed. V1 now reads 9V, V2 now reads 3V, and the ammeter reads
0.5A.
d) Determine the values of r, R1, and R2.
Open the switch and replace the two voltmeters with crappy non-ideal voltmeters each
with an internal resistance of 100Ω. Also replace the ideal ammeter with a non-ideal
ammeter with internal resistance 1Ω. The resistors r, R1, and R2 have the values you
determined in part d above.
e) Determine what V1, V2, and A read now.
Close the switch.
f) Determine what V1, V2, and A read now.
d
R
V
A
V2
K02. (Wolfson, Ch. 25 Problems 75 and 76) The figure at right below shows a portion of
a circuit used to model the electrical behavior of long, cylindrical biological cells such
as muscle cells or the axons of neurons.
a) Find the current through the “battery” V3, given that all resistors
have the same value R = 1.5 MΩ and V1 = 75 mV, V2 = 45 mV, and
V3 = 20 mV. Be sure to specify the direction of the current.
V1
V2
b) An electrochemical impulse traveling along the cell changes the
value of V3 so that now it supplies an upward current of 40 nA.
Assuming the rest of the circuit remains as described in part a), what is the new
value of V3?
Gustav R. Kirchhoff
1824-1887
V3