solved problems- electrostatics
TRANSCRIPT
كلية الهندسة Faculty of
Engineering
Physics II
(MP108)
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Solved Examples
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Question
?
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A charged comb often attracts small
bits of dry paper that then fly away
when they touch the comb. Explain.
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When the comb is
nearby, molecules in
the paper are
polarized and the
paper is attracted.
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During contact, charge from the comb is transferred to the paper by conduction.
Then the paper has the same charge as the comb, and is repelled.
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Question
?
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Where is the location
of +Q to be in equilibrium?
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Where is the location
of +Q to be in equilibrium?
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Where is the location
of +Q to be in equilibrium?
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Where is the location
of +Q to be in equilibrium?
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Where is the location
of +Q to be in equilibrium?
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Coulomb’s Law
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Problem No. 1
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Two identical
conducting small
spheres are placed
with their centers
0.3 m apart. One is
given a charge of
12 nC and the other
a charge of –18 nC.
a) Find the F exerted by
one sphere on the other.
b) The spheres are
connected by a
conducting wire.
Find the F each exerts
on the other after they
have come to
equilibrium
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F is Attraction Force
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b) The spheres are
connected by a
conducting wire.
Redistribution of
charges will be
occurred.
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After spheres have
come to equilibrium.
Each sphere has a
charge of
Repulsion Force
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Question
?
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A light, uncharged metallic sphere suspended from
a thread is attracted to a charged rubber rod.
After it touches the rod, the sphere is repelled by
the rod. Explain.
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First case
Final Case
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By induction
There are +ve charges on
near and –ve charges far sides of the sphere
Attraction force between sphere & rod is greater than Repulsion force between sphere & rod
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There is touch between
sphere and rod
Finally Repulsion force between sphere & rod
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Problem No. 2
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Four identical point charges particles (q = + 10 μC ) are located on the corners of a rectangle. The dimensions of the rectangle are L= 60 cm and W = 15 cm. Calculate the magnitude and direction of the total F exerted on the charge at the lower left corner by the other three charges.
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Problem No. 3
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Three point charges
are located at the
corners of an equilateral
triangle as shown in the
figure.
Calculate the total F
on the 2μ C charge.
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Problem No. 4
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Two known charges,
–12 μ C and 45 μ C,
and an unknown charge
are located on the x
axis. The -ve charge is
at the origin, and the
+ve charge is at
x = 15 cm.
The unknown charge
q is to be placed so
that each charge is in
equilibrium under the
action of the electric
forces exerted by the
other two charges.
Find the required
location, magnitude,
and sign of the q.
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With all my best wishes for
You
Dr.Mayssa Amin
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