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Gravitational Field
Force on mass
g = Field strength
g is in N/kg (9.81 N/kg on earth)
F = mg (g = F/m)
Electrical Field
Force on charge
E = Field strength
E is in N/C
F = qE (E = F/q)
Direction: Uh… down
Direction: F on + Charge
Force:
F = Gm1m2
r2
Field:
g = F = Gm
m
r2
Force:
G = 6.67x10-11 Nm2kg-2
k = 8.99x109 Nm2C-2
F = kq1q2
r2
Field:
E=F =
q
kq
r2
Example 1 - A +125 C charge experiences a force to the right of
.0175 N. What is the Electric field, and its direction?
Direction:
+q
Force This Way
E
Force This Way
140 N/C to the right
-q
Which way is the electric field? (wwpcd?)
+
+
+
+
+
-
Which way is the electric field?
-
+
+
+
+
+
Which way is the electric field?
+
Which way is the electric field?
+
-
Example 2 - An electron travels through a region where there is a
downward electric field of 325 N/C. What force in what direction
acts on the electron, and what is its acceleration?
5.21x10-17 N up
5.72x1013 m/s/s
Whiteboards:
Uniform field
1|2|3|4
Ishunta Dunnit notices that a charge of -125 C experiences a force
of .15 N to the right. What is the electric field and its direction?
E = F/q = (.15 N)/(-125x10-6 N) = -1200 N/C right or 1200 N/C left
1200 N/C left
Doan Botherme places a +12 mC charge into an upward 160 N/C
electric field. What force in what direction does it experience?
E = F/q, q = 12x10-3 C, E = 160 N/C up
F = 1.92 = 1.9 N up
1.9 N up
Alfred O. Dadark is on a planet where a mass of 0.12 kg
experiences a downward force of 7.80 N. What is the gravitational
field on the surface of this planet?
g = F/m, m = 1.12 kg, E = 7.80 N down
g = (7.80 N down)/(0.12 kg) = 65 N/kg down
65 N/kg down
Telly Vishun places an unknown charge into a known upward
electric field of 612 N/C, and the charge experiences a downward
force of .851 N. What is the charge?
E = F/q, E = 612 N/C up, F = .851 N down
q = -.0013905 C = -1.39 mC
-1.39 mC
Sal F. Hone levitates a .00125 kg ball with an upward electric field
of 590 N/C. What is the charge on the ball?
(Hint gravity = electrical force)
Eq = mg
E = F/q, F = Eq, F = mg, m = .00125 kg, g = 9.80 N/kg, E = 590 N/C
q = 2.07627E-05 = +20.8 C
+20.8 C