Induced Dipole

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Induced Dipole
In the presence of an electric field, a neutral
atom becomes polarized (i.e. an induced dipole).
Its dipole moment depends on how strongly the
nucleus attracts the electron cloud of the atom.
This quality is called polarizability, ?.
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Force on a neutral atom by a charged particle
1. The charged particle creates an electric field
at the location of the neutral atom.
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2. The electric field at the location of the
neutral atom polarizes the atom.
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3. The induced dipole creates an electric field
at the location of the charged particle.
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4. The force of the electric field (due to the
induced dipole) on the charged particle is
attractive
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Effect of an electric field on an insulator
Atoms in the insulator polarize.
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Effect of an electric field on an ionic solution
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Effect of an electric field on a metal
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in EQUILIBRIUM
Use the Superposition Principle.
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A negatively charged iron block is placed in a
region where there is an electric field downward
(in the y direction) due to charges not shown.
Which diagram best describes the charge
distribution in and/or on the iron block?
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A neutral copper block is polarized as shown, due
to an electric field made by external charges
(not shown). What is the direction of the net
electric field at location B, which is inside the
copper block?
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A neutral copper block is located near two balls
which have equal negative charges, as shown in
the diagram. What is the direction of the net
electric field at location A? Think carefully.
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Charging by induction
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A B are identical metal blocks. What is the
final charge of block B?

• 6 nC
• 3 nC
• 0
• -3 nC
• -6 nC

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1 2 are identical metal blocks. What happens?

• protons move from A to B
• electrons move from B to A
• both protons and electrons move
• no charges move

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Two aluminum blocks, A and B, are initially
neutral. They have insulating handles, which are
not shown. At a time after t4, what is the net
charge of A?

• positive
• negative
• neutral

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Practice Using the Superposition Principle
At point A, what is the net electric field? What
is the electric field due to the insulator? What
is the electric field due to surface charge on
the conductor?
A
insulator, uniform positive charge
neutral conductor
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Practice Using the Superposition Principle
At point B, what is the electric field due to the
insulator? What is the electric field due to
surface charge on the conductor? What is the net
electric field?
B
insulator, uniform positive charge
neutral conductor