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Two charges will exert a force on each other  (either a force of attraction or a force of  repulsion, depending on the charges):
Coulomb's Law
The force F between two charges is proportional to the product of the  charges and inversely proportional to the square of the distance between  them, r. The constant of proportionality, k, is called Coulomb's constant, and has  the value of 8.99 x 10 
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In groups of 2 or 3 complete the Venn Diagram
Newton's Law  Gravitation
Coulomb's Law Electrostatics
In 15 minutes you are allowed to walk around and look at other groups, you can make changes to yours and then you  get a chance to speak to your diagram, and you will havd it in
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Example #1
The two spheres in the above example are momentarily brought  together and then returned to their original separation distance.  Determine the electrostatic force now exerted by one charge on the  other.
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Example #2
The electrostatic force between  two charged  spheres is 3N   what would be the effect on the  force if:
a) the distance between the charges is doubled?
b)  The charge on one object is tripled  while the  other charge is halved?
c)   Both a) and b) occur at the same time?
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Hi nt In partners!
This is the end of Day one Check and Reflect  Page 538 #1­7
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Cool graphing skill
Graph this data X­Axis Y­Axis
make a new table with
appropriate for r!
This relationship is referred to as in inverse relationship
Inverse Relationships are defined as y =  1
x
The power on 'x' does not need to be 1 in  order to be called an inverse  relationship. In fact it can be 2,3,4,5...
If we consider coulomb's formula, with your partner suggest a power on x that would be appropriate?
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ight  lin e
Which means we can calculate the slope of this line.
The slope was useful in calculating 'k'.
Here is how Coulomb did it!
Obeying the formula will create graphs of straight lines
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Attachments
PRACTICE EXERCISE
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Note : Problems on gravitational forces are included for comparison.
1. Two students are sitting 1.50 m apart. One student has a mass of 70.0 kg and the other has a mass of 52.0 kg. What is the gravitational force between them?
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2. What gravitational force does the moon produce on Earth if the centres of Earth and moon are
3.88 x 108 m apart and the moon has a mass of 7.34 x 1022 kg?
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3. Calculate the electric force between two point charges of 4.00 µC and 3.00 gC when they are
2.00 cm apart . ( µC = microCoulomb , 1 µC =1 x 10 --6 C)
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Lesson 1-Electric Forces
4. Two points of equal charge produce an electric force on each other of 3.40x 10-2 N when placed
1 .00 x l 0-1 m apart. What is the charge on each point?
5. How far apart are two point charges of 2.0 x 10-6 C and 4 .0 x 106 C if they produce an electric
force on each other of 5.6 x 10-1 N?
6. Two point charged objects produce an electric force on each other of 6.20 x 10-2 N. What is the electric force if the distance between increases three times?
7. Two point charged objects produce an electric force on each other of 4.5 x 10-3 N. What is the electric force if the charge on both objects triple and the distance between them doubles?
ted I Not for Reproduction 73 Physics 30 SNAP
ELECTRIC FORCES AND FIELDS
8. Three point charged objects are placed in a line , as shown 0 .40 m 0.40 m
in the diagram . Calculate the magnitude of the net electric O O O force on the centre charge due to the other two charges . 2.0 x 10-6 C 2.0 x 10-" C 3.0 x 10--C
9. The electric force between two charged objects is 5.2 x 10-4 N when the objects are 3.11 x 10"1 m apart. What is the electric force between the same objects if the distance is changed to
4.04x101 m?
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10. Three point charged objects are placed at the corners of a right triangle, as shown in the diagram. Calculate the magnitude of the net electric force on the charge marked with the X due to the other two charges.
3.0x 1O-C 4.0x 10'C0 0 0.60 m
0.60 m
Lesson 1-Electric Forces
11. Two small spheres have the same mass and volume. One of the spheres has a charge of 4.00 gC and
the other sphere has a charge of -1.00 tC . If these two spheres are brought into brief contact with
each other and then separated to a distance of 2.00 x 10_I in, what is the electric force between them
at this distance?
12. Two small spheres, each with a mass of 2.00 x 10-5 kg, are placed 3.50 x 10-' in apart.
One sphere has a charge of -2.00 µC and is fixed in position. The other sphere has a charge of
-3.00 tC and is free to move without friction. What is the initial acceleration due to the electric
force on the sphere that is free to move?
13. Spheres A, B, and C are equally charged spheres lying along o o O
one line , as shown in the diagram . If the distance between spheres A and B is 1.5 cm, and the distance between spheres B and C is 4.5 cm, how does the force that sphere C exerts on sphere B compare with the force that sphere A exerts on sphere B?
Not for Reproduction 75 Physics 30 SNAP
ANSWERS AND SOLUTIONS
PRACTICE EXERCISE Answers and Solutions
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2.
(1.50Jm)2
=1.08x10-'N
. 2
(3.88x106 m
=1.94x102° N
(2.00x10-2 m)2
=2.70x102 N
2 Fer2
q k
8.99x109 C
ANSWERS AND SOLUTIONS
F 1 F2
to be the positive direction, then
F,,, =-3.37x10-' N+2.25x10-' N
=-1.1x10-' N, or 1. 1x10-' N to the left
9. l19z rz
To = 4.04x10' m =1.30
From 3.11 x 10' m Distance increases by a factor of 1.30.
Fe « (1.302
(0.60 m)z
=3.00x10-' N
= J(3.00x10-' N)z+(4.00x10-' N)2
2.00x10"' m)2
=5.06x10-' N
}
(3.50x10-' m)
=4.40x10-' N
(4.5)
1. E_kq r
[8.99X109 N . C^
z (8.00x10- C)
= 3.61 N/kg =3.61 kg*m = 3.61 m/s2 kg•s 2
6. F^
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SMART Notebook
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• Written Response -15%7
Show that the results verify Coulomb ' s Law by manipulating the data and providing a new table of values that , when plotted , will produce a straight-line graph.
• Plot the new data with the responding variable on the vertical axis.
• Calculate the slope of your graph.
• Using the slope value, or another suitable averaging techniques, determine the charge on sphere B if the charge on sphere A is 3.08 x 10-7 C.
• Determine the magnitude of the force between spheres A and B when they are at a distance of 2.00 in apart. Use the hypothetical value of 3.00 x 1e C for the charge on sphere B if you were unable to determine the actual value.
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Page 15: 1d slide #1
Page 16: 1d slide #2
Page 17: 1d slide #3
Page 18: 2-d electrostatics
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