7/28/2019 Classroom Assignment 5 With Answers
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Spring 2013
Physics 2 (PHYN002)
Classroom Assignment 5
2. (I) A service station charges a battery using a current of
6.7-A for 5.0 h. How much charge passesthrough the battery?
(Ans. 1.2x10 5 C)
3. (I) What is the current in amperes if 1200 Na + ions flow
across a cell membrane in 3.5 s? Thecharge on the sodium is the
same as on an electron, but positive. (Ans. 5.5x10 -11 A)
5. (II) An electric clothes dryer has a heating element with a
resistance of 8.6 . (a) What is the currentin the element when it
is connected to 240 V? (b) How much charge passes through the
element in 50min? (Assume direct current.) (Ans. 28 A, 8.4x10 4
C)
7. (II) A 4.5-V battery is connected to a bulb whose resistance
is 1.6 . How many electrons leave the battery per minute?(Ans.
1.1x10 21 electrons/minute)
8. (II) A bird stands on a dc electric transmission line
carrying 3100 A. Theline has 2.5 X 10 -5 resistance per meter, and
the bird's feet are 4.0 cm apart.What is the potential difference
between the bird's feet?(Ans. 3.1x10 -3 V)
9. (II) A 12- V battery causes a current of 0.60 A through a
resistor. (a) What is its resistance, and (b)how many joules of
energy does the battery lose in a minute? (Ans. 20 , 430 J)
10. (II) An electric device draws 6.50 A at 240 V. (a) If the
voltage drops by 15%, what will be thecurrent, assuming nothing
else changes? (b) If the resistance of the device were reduced by
15%, whatcurrent would be drawn at 240 V? (Ans. 5.5 A, 7.6 A)
11. (I) What is the diameter of a 1.00-m length of tungsten wire
whose resistance is 0.32 ?
(Ans. 4.7x10 -4 m)
12. (I) What is the resistance of a 4.5-m length of copper wire
1.5mm in diameter?(Ans. 4.3x10 -2 )
22. (II) A rectangular solid made of carbon has sides of lengths
1.0cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z
axes,respectively. Determine the resistance for current through the
solidin (a) the x direction, (b) the y direction, and (c) the z
direction.Assume the resistivity is = 3.0 X 10 -5 .m.
(Ans. a) 3.8x10 -4 , b) 1.5x10 -3 , c) 6x10 -3 )
7/28/2019 Classroom Assignment 5 With Answers
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23. (II) A length of aluminum wire is connected to a precision
10.00-V power supply, and a current of 0.4212 A is precisely
measured at 20.0C. The wire is placed in a new environment of
unknowntemperature where the measured current is 0.3818 A. What is
the unknown temperature?
(Ans. 44.1 oC)
27. (III) Determine a formula for the total resistance of a
spherical shell made of material whose
conductivity is and whose inner and outer radii are r 1 and r 2.
Assume the current is radially outward.
(Ans.
)
30. (III) A hollow cylindrical resistor with inner radius r1 and
outer radius r2, and length , is made of a
material whose resistivity is . (a) Show that the resistance is
given by
( ) for currentthat is radially outward. [Hint: Divide the
resistor into concentric cylindrical shells and integrate.]
(b)Evaluate the resistance R for such a resistor made of carbon
whose
inner and outer radii are 1.0 mm and 1.8 mm and whose length is
2.4cm. (Choose = 15 X 10 -5 m.) (c) What is the resistance in part
(b)for current flowing parallel to the axis?
(Ans. 5.8x10 -4 , 0.51 )
31. (I) What is the maximum power consumption of a 3.0-V
portable CD player that draws a maximumof 270 mA of current? (Ans.
0.81 W)
32. (I) The heating element of an electric oven is designed to
produce 3.3 kW of heat when connected
to a 240-V source. What must be the resistance of the
element?(Ans. 17 )
57. (II) A 0.65-mm-diameter copper wire carries a tiny current
of 2.3 A. Estimate (a) the electron driftvelocity, (b) the current
density, and (c) the electric field in the wire. (Ans. 5.1x10 -10
m/s, 6.9 A/m 2,1.2x10 -7 V/m)
58. (II) A 5.80-m length of 2.0-mm-diameter wire carries a
750-mA current when 22.0 m V is appliedto its ends. If the drift
velocity is 1.7 X 10 -5 m/s, determine (a) the resistance R of the
wire, (b) theresistivity , (c) the current density j, (d) the
electric field inside the wire, and (e) the number n of
freeelectrons per unit volume.
(Ans. 0.029 , 1.6x10 -8 .m, 2.4x10 5 A/m 2, 3.8x10 -3 V/m
,8.8x10 28 electrons/m 3)
