Download Electric charges and voltage

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Physics 100
Lecture 8
Electric Charges and
Potential
February 15, 2017
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Written Quiz – Chapter 4b
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Timer applet
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About the exam
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Bring a calculator and a No.2 pencil. No cell phone
calculators are allowed!

I will provide the equations (no need to memorize
them) and any constants (like acceleration of gravity,
R-value, etc.) you may need
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About four numerical problems worth 35 points.
Write symbolic formula, show steps leading to
answer, present answer with units for full credit
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Ten true/false questions worth 20 points
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Fifteen multiple-choice questions worth 45 points. A
few of these may require a simple calculation or ratio
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Electric charges
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Two kinds of electric charge
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Charges exert
forces on each
other according to
Coulomb’s Law
• Positive (protons)
• Negative (electrons)
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Coulomb’s Law
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Force is proportional to the product of
the charges and inversely proportional to
the square of the distance.
Like charges repel, unlike charges
attract
Interactive applet
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Voltage
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It takes work to move charges around
against the repulsive or attractive forces
That work is stored as electric potential
energy
The work per charge is called the electric
potential, and it’s measured in volts.
1 Joule
1.0 Volt 
1 Coulomb
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Electric potential
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The electric
potential can be
pictured in terms of
an energy surface,
where electric
potential is similar
to gravitational
potential energy.
Interactive applet