Jim Guinn’s PHYS2212 Assignment #2 Solutions
1.
A charge of 3.00
μ
C is at the point (2.00m, 3.00m), what is the electric field vector,
E
, at
the point (5.00m, 4.00m)?
The distance from the charge to the point is given by
r
2
= (7.00m)
2
+ (1.00m)
2
= 50.0m
2
, so
r = 7.07m .
The magnitude of the electric field is given by
E = k Q/r
2
= (8.99x10
9
N m
2
/C
2
) (3.00x10
6
C) / (7.07m)
2
= 539 N/C .
The electric field points toward the charge at an angle of
tan
θ
= (1.00m/7.00m) = 0.143, so
θ
= 8.13
o
below the –x  axis, so
E
= 539 N/C at an angle of 8.13
o
below the –x  axis.
2.
A charge of 3.00
μ
C is at the point (4.00m, 2.00m), what is the electric field vector,
E
, at
the point (5.00m, 4.00m)?
The distance from the charge to the point is given by
r
2
= (1.00m)
2
+ (6.00m)
2
= 37.0m
2
, so
r = 6.08m .
The magnitude of the electric field is given by
E = k Q/r
2
= (8.99x10
9
N m
2
/C
2
) (3.00x10
6
C) / (6.08m)
2
= 729 N/C .
The electric field points away from the charge at an angle of
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tan
θ
= (6.00m/1.00m) = 6.00, so
θ
= 80.5
o
above the x  axis, so
E
= 729 N/C at an angle of 80.5
o
above the x  axis.
3.
A charge of 3.00
μ
C is at the point (2.00m, 3.00m) and a of charge of 3.00
μ
C is at the
point (4.00m, 2.00m), what is the electric field vector,
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 Fall '11
 JimGuinn
 Electric charge, Fundamental physics concepts, tanθ

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