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Week 8 – Group Work, 3 questions to be assigned:
Choose one of:
1. Currents up to 30A can be carried by 10 gauge (area= 5.26 mm2 ) copper wire
a) What is the resistance of 100m of 10 gauge copper wire? (= 1.68x10-8 m)
b) What is the electric field in the wire when the current is 30A?
c) How long does it take for an electron to travel 100 m in the wire when the current is
30A?
For Cu, n= 8.47x1028 atoms/m3 (from density = 8.93 g/cm3, molar mass 63.5
and one free electron per atom)
2. (Chap 25 P52) A 5.0 m length of 2.0 mm diameter wire carries a current of 0.75 A when
22.0 mV is applied to its ends. If the drift velocity is 1.7x10-5 m/s, determine:
a) the resitance, R, of the wire
b) the resistivity 
c) the current density, j
d) the electric field within the wire
e) the number, n, of free electrons per unit volume.
Choose one of:
1. (Chapt 24 P5) The charge on a capacitor increases by 16C when the voltage across it
increases from 28 V to 48 V. What is the capacitance of the capacitor?
How many different ways can you combine four 100  capacitors. Determine the equivalent
capacitance for each case.
Choose one of:
1. For the following circuit, C1 = 1.0 F, C2 = 2.0 F, C3 = 3.0 F, C4 = 4.0 F. 12 V ideal
battery.
C1
C3
S1
C2
S2
C4
Find the charge on each capacitor when
a) only S1 is closed
b) when S2 is also closed
2. For the following circuit, C1 = 4.0 F, C2 = 5.0 F, C3 = 6.0 F, C4 = 7.0 F. 20 V ideal
battery.
C1
C3
C2
S2
C4
S1
Find the charge on each capacitor when
a) only S1 is closed
b) when S2 is also closedWeek 8 – Hand-in Questions – 3 problems to be assigned
Choose one of:
1. True or false, if the statement is true explain why it is true, if false give a counter
example. The capacitance of a parallel plate capacitor depends on the potential
difference between the plates?
2. True or false, if the statement is true explain why it is true, if false give a counter
example. The capacitance of a capacitor is defined as the total charge that it can hold?
3. (Chap 24 Q 10) How does the energy in a capacitor change if
a) the potential difference is doubled
2
3
b) the charge on each plate is doubled
c) the separation of the plates is doubled as the capacitor remains connected to the
battery
Choose one of:
1.
(Chap 24.P36) Two capacitors C1 = 3200 pF and C2 = 2200 pF are connected in series to a
12.0-V battery. The capacitors are later disconnected from the battery and then connected
directly to each other, positive plate to positive plate, negative plate to negative plate. What
then will be the charge on each capacitor?
2. (Chap 24 P34 Two capacitors connected in parallel produce the equivalent capacitance of
35 F but when connected in series the equivalent capacitance is only 4.0F. What is the
individual capacitance of each capacitor?
Choose one of:
1. (Chap 25 P68) A 1.0  wire is drawn out to 3.00 times its original length. What is its
resistance now?
2. (Chap 25 P 64) the wiring in a house must be thick enough so it doesn’t became so hot as to
start a fire. What diameter must a copper wire be if it is to carry a maximum current of 30 A
and produce no more than 1.6 W of heat per meter of length? (Cu= 1.68x10-8 m)