Electric Potential Difference
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Transcript of Electric Potential Difference
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Electric Potential Difference
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Electric Potential Energy (PE)
Potential energy associated with a charged object due to its position relative to a source of electric force. Changing the position of the charge in the electric field changes
its PE. A larger test charge has a greater PE
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Electric Potential Difference (∆V)
The work done moving a charged particle divided by the charge of the particle.As the value of a charge in a field increases,
the value of PE also increases. Electric potential difference is independent of charge at a given point.
∆V = Won q / q Units = J/C = Volts (V)
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Electric Potential Difference (∆V)
The sign of the charge and the direction of the field determines if ∆V is positive or negative. ∆V is negative if the charge is moved in the same
direction as the net force (negative work done). ∆V is positive if the charge is moved opposite the
direction of the net force (positive work done). ∆V is zero if the charge is moved perpendicular to
field lines (no work done). These points are called equipotentials.
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Some Points to Remember:
Electric potential difference is also called potential difference or voltage.
The potential difference between two points can be measured using a voltmeter.
The zero point for potential can be arbitrarily assigned. Points that are grounded are usually assigned a
potential of zero.
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Electric Potential Difference in a Uniform Field
V = (Vb – Va) = Won q / q = (Fd) / q F=Eq = (Eq)d /q
V = Ed d = displacement parallel to
the field lines
+qA B
d
E
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Electric Potential Difference in a Uniform Field
Charges that move parallel to the field lines experience changes in potential.
Charges that move perpendicular to the field lines do not experience changes in potential. NOTE: A potential
difference exists between points in a field even if there is no charge at those points.
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A charge moves 2.0 m parallel to the direction of a uniform electric field with a field strength of 1.0 x 103 N/C. What potential difference does the charge move through?Given: E = 1.0 x 103 N/Cd = 2.0 mFind: ΔV = ?
V = Ed= (1.0 x 103 N/C)(2.0 m)= 2.0 x 103 V
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Robert A. Millikan’s Oil Drop Experiment (1909)
Millikan found that charge always occurred in multiples of 1.60 x 10-19 C (the elementary charge)
He concluded that charge is quantized
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Capacitor
A device that stores electric energy and electric charge. Made of 2 conducting plates separated by some distance,
each with equal but opposite charge. Insulating material is often placed between the plates.
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Capacitance (C) The ability of a capacitor to store energy.
It is the ratio of the amount of charge stored on each plate to the potential difference between the plates.
C = q / ∆V Units = farads (F) 1 F = 1 C / V Since farads are large, microfarads (F) or
picofarads (pF) are used. (1 pF = 10-12 F)
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Some Uses for Capacitors
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In a defibrillator, a 10. F capacitor is connected to a potential difference of 6000. V. What is the charge stored in the capacitor?
Given: C = 10. F = 10. x 10 -6 F ∆V = 6000. V Find: q =?
C = q /∆VC(∆V) = q = (10. x 10 -6 F )(6000. V)= 0.060 C