Practice Problems
Electric fields
Directions:
On this worksheet you will investigate properties of electric fields.
omit
Question 1
Which set of equations correctly describes the electric fields in this diagram? The central +4 point charge has no dimension.
r < r
_{1}
r
_{1}
< r < r
_{2}
r > r
_{2}
A
E = 0
E = k(12q)/r
^{2}
E = k(8q)/r
^{2}
B
E = k(4q)/r
^{2}
E = 0
E = k(12q)/r
^{2}
C
E = k(4q)/r
^{2}
E = k(8q)/r
^{2}
E = 0
D
E = k(4q)/r
^{2}
E = 0
E = k(8q)/r
^{2}
A
C
B
D
omit
Question 2
If a charge of +20 µC is placed in an uniform electric field having a strength of 7000 N/C, it will experience a force of
1.4 x 10
^{-1}
N, up
3.5 x 10
^{8}
N, up
1.4 x 10
^{-1}
N, down
2.86 x 10
^{-9}
N, down
3.5 x 10
^{8}
N, down
2.86 x 10
^{-9}
N, up
omit
Question 3
If the central charge is +5 µC, and point B is 20 cm away, what is the magnitude of the electric field strength at point B?
2.25 x 10
^{5}
N/C
1.13 x 10
^{6}
N/C
1.13 x 10
^{2}
N/C
2.25 x 10
^{3}
N/C
omit
Question 4
According to the diagram shown below, what is the ratio of the magnitude of the left charge compared to the magnitude of the right charge?
1.6
0.375
0.6
0.625
omit
Question 5
What magnitude electric field is required in a cathode ray tube to accelerate electrons from 0 to 2.1 x 10
^{7}
m/sec in a distance of 2.5 cm?
8.82 x 10
^{15}
N/C
5.02 x 10
^{2}
N/C
5.02 x 10
^{4}
N/C
1.55 x 10
^{27}
N/C
omit
Question 6
In
Question 5
, through how large a potential difference does the electron travel while accelerating?
2.01 x 10
^{2}
volts
1.26 x 10
^{3}
volts
2.21 x 10
^{14}
volts
1.48 x 10
^{7}
volts
omit
Question 7
In Millikan’s oil drop experiment, if the electric field between the plates was adjusted to the right magnitude, it would exactly balance the weight of the drop. Suppose a tiny spherical oil droplet of radius 2.1 x 10
^{-6}
meters carries a charge equivalent to two electrons. What electric field is required to balance the weight? (The density of oil is 850 kg/m
^{3}
.)
1.77 x 10
^{17}
N/C
1.19 x 10
^{3}
N/C
2.02 x 10
^{6}
N/C
1.01 x 10
^{6}
N/C
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