• Check answers – a few were found to be
wrong…possibly reword the definition/law
questions
Electrostatics JEOPARDY
Powell
Augustine
Head
Brown
Williams
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Balloons X , Y and Z are hanging as shown. Balloon X is positivelycharged
Balloon Y ____.
A must be positivelycharged
D could be either
negatively-charged or
neutral
B must be negativelycharged
E could be either
positively-charged or
neutral
C must be neutral
A
What is
D. could be either
negatively-charged
or neutral?
The charge an electrophorus
would gain if the base was made
out of glass.
A
What is
Negative?
The reason that scraps of paper
jump up and down and back
up when a charged plastic rod is
brought near.
A
What is
The pieces become polarized, are
attracted to the rod, and jump up.
When they touch, the charge is
transferred to the piece, giving it
the same charge. The attraction
stops. When it touches ground, it
looses its charge, allowing it to
become polarized again ?
Explanation of the basic process
of charging an electroscope.
A
What is
A charged object is touched to
the ball of the electroscope. The
charges are transferred and
travel across the bars
of the scope, causing
it to repel ?
Explanation of how one’s hair
raises when you touch the Van
de Graaff generator.
A
What is
Negative charges travel from the
Van de Graaff generator onto
one’s body as they try to get as
they try to spread out.
When on your hair,
they cause it to raise
up as they try to repel
as far as possible ?
The magnitude of the force of a
+25µC charge on a -50µC
charge 20 cm away.
+25µC
-50µC
22cm
A
k Q1Q2
F = r2
What is
2.81 x 102 N ?
2
Nm
9x109 C2 (50 x 10-6 C) (25 x 10-6 C)
= 2.81 x 102 N
(.20 m)2
The magnitude of the force 10
electrons would apply on 4
protons at a distance of 1µm.
Hint…qe=1.6x10-19 C
A
What is
9.22 x 10-15 N ?
2
Nm
9x109 2 [4(1.6 x 10-19 C)] [10(1.6 x 10-19 C)]
C
= 9.22 x 10-15 N
(1 x 10-6 m)2
k Q1Q2
F = r2
The force applied on the farthest
right charge by the other two
charges.
+8µC
-6µC
7mm
+5µC
3mm
A
k Q1Q2
F = r2
What is
2.64 x 104 N left ?
2
Nm
9x109 C2 (8 x 10-6 C) (5 x 10-6 C)
F13 =
-3 m)2
(10
x
10
2
Nm
9x109 C2 (6 x 10-6 C) (5 x 10-6 C)
F23 =
(3 x 10-3 m)2
F23 + F13 = 2.64 x 104 left
= 3.6 x 103 N
= 3 x 104 N
The number of electrons you
would need to put on
electrostatic flying boots to
make a 70kg person hover at a
height of 2 m above a charge of
-50 mC.
Ahhh..
I’m
flying!
A
What is
2.38 x 1012?
k Q1Q2
F = r2
F = 70kg (9.81 m/s2) =
2
Nm
9x109 2 (-50 x 10-3 C)[n(-1.6 x 10-19 C)]
C
(.20 m)2
n = 2.38 x 1012
The force on the orange charge.
+4.6 C
-5.4 C
2.5 m
+ 7.2 C
4m
2m
5m
-5.4 C
+4.6 C
A
k Q1Q2
F = r2
What is
0N?
Diagonal forces cancel each
other out, resulting in a net
force of 0N on the orange
charge.
No net electric charge can be
created or destroyed.
A
What is
The law of conservation of
electric charge ?
+1.6 x 10-19 C
A
What is
The Charge of a proton ?
The charging of an isolated
conducting object by grounding
it while a charged body is
nearby.
A
What is
Induction ?
The force F exerted on a tiny
positive test charge placed
divided by the magnitude of the
test charge.
A
What is
Electric Field, E ?
F
E=
q
Two equally charged charge that
have the opposite charge.
A
What is
A dipole ?
The charge of the orange charge
Followed by
The charge of the blue charge
A
What is
Positive (orange), negative (blue) ?
Charge on the blue charge
|Q|=4.7 x 10-4 C
A
What is
-3.5 x 10-4 C ?
4.7 x 10-4 C
?
|Q|=4.7 x 10-4 C
=
8 lines
6 lines
The number of lines that
should point outwards from
the orange plate.
?
?
BE
CAREFUL!!!!
A
What is
0?
Follow up question
How many lines
should point inwards?
8 lines
?
8 charges = 6 charges
Charges of point charges in order
(orange, blue, green, white)
A
What is
--++?
Orange
Blue
Green
White
Minimum of 2 errors in the
following drawing, with
explanations of error.
2C
2C
A
What are
Wrong direction of field lines
(should go from positive to
negative) and
Wrong number of field lines
(should be equal as charge is
equal) ?
E-Field at X below
12 C
15m
A
What is
6 x 108 N/C left ?
kQ
E= 2
r
2
Nm
9x109 C2 (12 C)
= 6 x 108 N/C
(15 m)2
12 C
15m
Approximate location of E=0 N/C
on line between orange and blue
charge
12 C
24 C
15m
A
What is
Somewhere between orange and
mid point (7.5m to the right of
orange) ?
E=
kQ
r2
12 C
24 C
15m
The E-Field at the X
12 C
24 C
15m
10 m
A
kQ
E= 2
r
What is
2.33 x 109 N/C right ?
E12C
E24C
Nm2
9x109 C2
2
Nm
9x109 C2 (24 C)
(10 m)2
(12 C)
= 1.7 x 108 N/C
(25 m)2
12 C
24 C
15m
10 m
= 2.16 x 109 N/C
The letter which denotes the
location with the greatest
magnitude of E-Field
B
C
D
4m
3m
2m
Q=18C
Q=7C
A
1m
Q=1.5C
Q=24C
A
kQ
E= 2
r
What is
C?
k (1.5C)
2
EA =
=1.5k
C/m
(1m)2
k (24C)
2
EB =
=1.5k
C/m
(4m)2
k (18C)
2
EC =
=2k
C/m
(3m)2
k (7C)
2
ED =
=1.75k
C/m
(2m)2
The E-Field at the orange point.
-4 C
-5 C
2.5 m
5m
2.5 m
5m
-5 C
+4 C
A
What is
kQ
E= 2
r
5.77 x 109 N 45 degrees N of W ?
3.53m=r
2.5m
2.5m
2
Nm
9x109 C2 (4 C)
(3.53 m)2
= 2.89 x 109 N
FINAL JEOPARDY
The complete process for charging an
electrophorus using proper terminology.
(5 minutes)
TIE BREAKER
WHAT IS THE SIGNIFICANCE OF THE
CATEGORY TITLES?
2004 Illini Basketball Starters
(when we should have won the
NCAA tourney)