Physics 202 Homework, Day 11: Chapter 17: #1,10,11,14
ü 1. If a current of 80.0 ma exists in a metal wire, how many electrons flow past a given cross-section of the
wire in 10.0 min?
In what direction do the electrons flow with respect to the current?
In[10]:=
current = 80 * 10-3 ; time = 10 * 60.;
charge = current * time ;H* coulombs *L
electrons = charge ë I1.6 * 10-19 M; Print@electrons, " electrons"D
3. µ 1020 electrons
ü 10. An electric heater carries a current of 13.5 A when operating at a voltage of 1.2 x 102 V. What is the
resistance of the heater?
In[8]:=
current = 13.5; voltage = 120.;
resistance = voltage ê current; Print@resistance, " Ohm"D
8.88889 Ohm
ü 11. A person notices a mild shock if the current along a path the thumb and index finger exceeds 80 µA.
Compare the maximum possible voltage without shock across the thumb and index finger with a dry-skin
resistance of 4.0 x 105 W and a wet skin resistance of 2000W.
In[19]:=
current = 80 * 10-6 ; resistance1 = 4. * 105 ;
voltage1 = current * resistance1; Print@voltage1, " Volts"D
resistance2 = 2. * 103 ; voltage2 = current * resistance2; Print@voltage2, " Volts"D
32. Volts
0.16 Volts
ü 14. Eighteen guage wire has a diameter of 1.024 mm. Calculate the resistance of 15 m of 18 guage copper
wire at 20 °C. (r = 1.7 x 10-8 W-m )
In[23]:=
2
crossSection = p I1.024 * 10-3 M ; length = 15.`; resistivity = 1.7 * 10-8 ;
resistance = resistivity *
0.0774088 Ohm
length
crossSection
; Print@resistance, " Ohm"D