Download Fields and Potential Energy

Potential Energy
Physics 12
Potential Energy
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In grade 11 physics we looked at
Gravitational Potential Energy
Formula: Eg = mgh
W = Fgd
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Work and Energy are measured in Joules
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When an object falls, its Eg is converted
from gravitational potential energy to
kinetic energy or work.
Electric Potential Energy
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Electrical Potential Energy (EQ) is stored
by doing work against electrostatic force.
This can be done by separating
attractive/unlike charges (as in a battery)
or forcing together like charges (as in a
capacitor).
If you move a charge in an electric field,
you must apply a force. Applying a force
causing displacement means that work is
done. If you do work, then the object
gains energy. Moving a charge is an
example of electric potential energy.
Electric Potential Energy
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Note: Eq can be +
or – (depends on
the charge)
** Write on your
formula sheet!
W  EQ  Fe d
kq1q2
EQ 
r
Voltage (V)
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The work done per unit charge in
moving a charge between two points
in an electric field
Voltage is a measure of how
electrical potential energy is
delivered
Voltage is also called electrical
potential difference
Voltage
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V = W/q or V = Ee/q
Units of V = volts
1 Volt = 1 Joule/Coulomb
Example: Batteries
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Batteries achieve separation of
charge in an anode and cathode
separated over a distance.
Batteries are not rated by how much
potential energy they contain but by
how much energy they can deliver as
current flows (voltage)
Example 1
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A battery has a potential difference
of 18.0 V. How much work is done
when a 64.0 C charge moves from
the anode to the cathode?
1150J
Example 2
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A potential difference of 10V exists
between 2 points, A and B, within an
electric field. What is the magnitude
of charge that requires 2.0 x 10-2 J of
work to move it from A to B?
0.0020 C
Electron volts
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One electron-volt (eV) is the energy
needed to move one elementary
charge through a potential difference
of 1V.
1 eV = 1.6 x 10-19 J
Example 3
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A charge of 2.0 x 10-3C is moved
through a potential difference of 10
volts in an electric field. How much
work, in eV, was required to move
this charge?
W = 1.25 x 10
17
eV
Try these
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1) How much electrical energy is required to
move a 4.0 microCoulomb charge through a
potential difference of 36V?
2) In an electric field, 0.90 J of work is required
to bring 0.45 Coulombs of charge from point A to
point B. What is the electric potential difference
(voltage) between points A and B?
3) A single proton is moved through a potential
difference of 10 volts in an electric field. How
much work, in electronvolts, was required to
move this charge?
HINTS
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Remember that work is equal to
change in energy (look on your
formula sheet for formulas for kinetic
energy, gravitational, etc)
Voltaic Cell
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One of the silver, zinc and salt water
soaked discs became known as a
voltaic cell
A voltaic cell requires:
• Cathode (positive end)
• Anode (negative end)
• Electrolyte (to allow the movement of
charge)