E&M Final Review
Look at the E&M Unit reviews as well
U1 Charge
1.Compare the electrostatic force between an electron and proton separated by 5.30×10−11 m with
the gravitational force between them. This distance is their average separation in a hydrogen atom
Fe = 8.2×10–8 N , Fg = 3.6×10–47 N Fe is about 1040greater than Fg
2.Calculate the strength and direction of the electric field E due to a point charge of 2.00 nC (nanoCoulombs) at a distance of 5.00 mm from the charge.
E= 7.2×105 N/C.
3.What force does the electric field found in the previous example exert on a point charge
of –0.250 µC ?
F = 0.180 N.
4.If steps are not taken to ground a gasoline pump, static electricity can be placed on gasoline when
filling your car's tank. Suppose a tiny drop of gasoline has a mass of 4.00×10 –15 kg and is given a
positive charge of 3.20×10–19 C . (a) Find the weight of the drop. (b) Calculate the electric force on
the drop if there is an upward electric field of strength 3.00×10 5 N/C due to other static electricity
in the vicinity. (c) Calculate the drop's acceleration. A)= 3.92×10−14 N, b = 9.60×10−14 N,
c = 9.5 m/s2
5. A 5.00 g charged insulating ball hangs on a 30.0 cm long string in a uniform horizontal electric field
directed to the right. The ball swings to the right at an 8°angle.Given the charge on the ball is 1.00
µC , find the strength of the field.
E=6900N/C
U2 potential
6.Suppose you have a 12.0 V motorcycle battery that can move 5000 C of charge, and a 12.0 V car
battery that can move 60,000 C of charge. How much energy does each deliver?
cycle= 6.00×104 J. car = 7.20×105 J.
7.Calculate the final speed of a free electron accelerated from rest through a potential difference of
100 V. (Assume that this numerical value is accurate to three significant figures.) = 5.93×106 m/s.
8.An electron gun has parallel plates separated by 4.00 cm and gives electrons 25.0 keV of energy.
What is the electric field strength between the plates? (b) What force would this field exert on a
piece of plastic with a 0.500 μC charge that gets between the plates? A) E = 6.25×105 V/m
b) F = 0.313 N.
9. What is the voltage 5.00 cm away from the center of a 1-cm diameter metal sphere that has a
−3.00 nC static charge?
V = –540 V.
Circuits
10. During open-heart surgery, a defibrillator can be used to bring a patient out of cardiac arrest. The
resistance of the path is 500 Ω and a 10.0-mA current is needed. What voltage should be applied?
5.0V
11.Find the voltage drop in an extension cord having a 0.0600- Ω resistance and through which 5.00
A is flowing. A cheaper cord utilizes thinner wire and has a resistance of 0.300 Ω . What is the
voltage drop in it when 5.00 A
.3v, 1.5v
12. What power is supplied to the starter motor of a large truck that draws 250 A of current from a
24.0-V battery hookup?
P=6000w
13. Sketch a schematic for a series circuit with a 12.0 V battery and 3 resistors of 1.00 Ω , 6.00 Ω , and
13.0 Ω.
a) What is the total resistance of the circuit ? b) calculate the total current of the circuit.
c) Calculate the voltage drop in each resistor, and show these add to equal the voltage output of the
source. d) Calculate the power dissipated by the circuit and in each resistor.
a) = 20.0 Ω, b) = 0.600 A, c) V1=.6V, V6=3.6V, V13= 7.8V d) Pt = 7.20 W, P1 = 0.36 W, P6 = 2.2 W,
P13 = 4.7 W
14. Sketch a schematic for a parallel circuit with a 12.0 V battery and 3 branches. Each branch has
one resistor, the resistors are 1.00 Ω , 6.00 Ω , and 13.0 Ω. a) What is the total resistance of the
circuit? b) Calculate the total current in the circuit. c) Calculate the current in each resistor, and
show these add to equal the total current output of the source. d) Calculate the power dissipated
by the circuit and in each resistor. A)= 0.80 Ω , b) = 15 A, c) I1= 12 A, I6= 2 A, I13= 0.92 A
d) Pt = 180 W, P1 = 144 W, P6 = 24 W, P13 = 11.1 W