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22 Cards in this Set
- Front
- Back
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System's potential energy
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increases by the amount of work done. To bring an object to a higher potential energy (like raising a book with your hand) requires work. This is the work provided by your muscles and transferred to t he system. This energy is released when the book is dropped.
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Source charges
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charges that are fixed in place and don't move
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Electric potential energy (Uelec)
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In a similar way to gravitational potential energy, "pushing" (if you can imagine holding an electron in your hand in the same way you hold a book) a point charge towards a charge of the same sign requires work
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Electric potential (text book definition)
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Energy stored in a system of charged particles due to their electrical interactions.
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What is meant by a "system of charges"
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a system of several charges, only one of which moves. As this charge moves, it is the the electric potential energy of the system of charges- moving and fixed- that actually changes.
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Zero of Electric Potential Energy
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Like with gravitational potential energy, we are only concerned with changes in potential energy itself. Therefore where U=0 is totally arbitrary.
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electric fields...
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exist whether or not there is a charge q present to experience the force
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electric potential energy and distance
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in general, a particle's electric potential energy (and therefore its work) is proportional (directly, linearly, in y=x fashion) to its charge. Double the charge and the U (or W) will also double the work to bring those charges together. Therefore, you will double the electric potential energy since U is proportional to W.
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Electric Potential
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Tells you how to find the potential energy for any charge that happens to be placed at some point. (Recall that every point in space has a potential energy associated with if a particle of that charge was placed in that location). The potential for creating potential energy. At any point ini an electric field, the electric potential energy at that point depends on the electric potential and the magnitude of the point charge that moves. the electric potential is defined as V.
V = W(joules)/q(Coulomb's) where V is in J/C or volts 1 volt= 1 V = 1 J/C |
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Distinguishing electric potential from electric potential energy
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Whereas electric potential is a measure of source charges and measured in J/C or Volts, electric potential energy is the interaction energy of a charged particle and a source charge and is measured in Joules.
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Crucial detail to electric potential
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The electric potential does not depend on any charge q (a stationary charge in an electric system). Instead it depends on the source charge (The charge you "move" in your hand). Like an electric field, the electric potential exists throughout space whether or not charge q happens to be present
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Electric Potential Energy
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Uelec = qV
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change in Uelect
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Uchange = Ufinal - Uinitail
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What does the sign of U mean
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The higher the U, the more potential energy. Negative U means lower potential energy. Going from higher to lower potential energy means the charged particle lost potential energy (and gave it off to the environment?)
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Sign of electric potential, V
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If you take a positive test charge from your pocket, and "probe" the potential, you'll find that the electric potential gets more positive as a positive (source, fixed) charge is approached. Similarly, the electric potential gets more negative as you approach a negative charge.
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"Mapping" electric potential. Contour lines And equipotential lines
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Similar to mapping mountains. Like contour lines on a map which are drawn through points with the same elevation, contour lines on a potential map are drawn through point with the same electron potential, these contours are called equipotential lines
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Energy and velocity: The speed of a charge is dependent on the direction of increasing V, electron potential
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Because energy is conserved, a charge slows down when it moves through a region of lower potential to an area of higher potential. And vice versa. A particle speeds up moving from a high to a low potential for the same reason.
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Potential Difference
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Moving from a high to a low potential is a positive potential difference where as from low to high potential is a negative potential difference. Potential difference is Delta V = Vf - Vi
and is often called voltage |
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Electric Potential Energy and Potential difference
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Delta U = qDeltaV
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Conservation of Energy
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ΔE_mech= 0 = ΔK + ΔU = ΔK + qΔV= 0
___OR___ K_f + qV_f = K_i + qV_i Where K_f and K_i are the total kinetic energies of all moving particles |
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Solving conservation of Energy Problems
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1. Draw a before and after picture
2. Use K_f + qV_f = K_i + qV_i (conservation of energy) 3. Addition conservation laws, such as the conservation of charge and conservation of momentum may need to be used. |
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Electron Volt
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1 electron volt = 1eV = 1.60 * 10^-19 J
The kinetic energy gained by an electron(or proton) if it accelerates through a potential difference of one volt. Not to be confused with volts. Volts are a measure of potential in J/C, electron volts are a measure of energy, J. |
