IV . Electric ______________ Potential Move some _______________ from point A to B in the E ( ________________ ) field of a charged object: charge q electric E field ________ lines A q charged object F B  It takes ____________ to move q closer because it requires a ____________ applied for a ______________ . work W force F distance d

Because of the work done, the energy of the ___________of charges is stored up as an electric _______ . system PE The electric _______________________ V is defined as the work done per charge: potential difference V = W / q scalar no direction V is a _____________ because it has ___________________ units of V: By definition, one _______________________ = 1 _________ or 1 _______ = 1 _____ [V] = [ ] / [ ] W q [V] = / J C joule/coulomb volt J/C V  Because of its units, the potential difference is often called the ________________ . voltage

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Ex 1: 18 J of work are required to move 2.0 C of charge between two points in an electric field. Find the electric potential difference between the two points. Given: 18 J = W V = W / q V = 18 J /2.0 C = 9.0 J/C = 9.0 V 2.0 C = q V = ? How much work would be required to move 4.0 C of charge between the same two points of the problem above? V = W / q = q = 4.0 C V = 9.0 V 9.0 V W/ 4.0 C W = ? 36 J W How much potential energy is stored up as a result? 36 J

DC volts in different sizes and shapes:

AC volts in different sizes and shapes:

NOTE: V = W/q can be used with 2 sets of units! When working with small amounts of charge and energy, you often use _______________ units. For W, instead of joules, use units: ______________________ For q, instead of coulombs, use units: the number of ______________________ Using these new units, the potential difference V in: V = W/q will have units: [ V ] = [ ] / [ ] which again be volts: = / You get V because _________________ . smaller electronvolts, eV elementary charges, e q W V eV e the e's cancel

Ex: 20 electronvolts of work are required to move 8 electrons between two points in an electric field. Find the electric potential difference between the two points V = W / q = 20 eV / 8 e = 2.5 eV/e = 2.5 V Given: 20 eV = W 8 e = q V = ? Ex: How much work (in eV) is done on a proton when it is accelerated through a potential difference of 68,000 volts? V = W / q = / 68,000 V W 1 e  W = 68,000 eV How much kinetic energy will the proton have as a result? DKE = W = 68,000 eV

Conversions between units. See PhysRT, page ____: 1 electronvolt (eV) = _____________________ J Notice that this number is the same as the one in the conversion: 1 elementary charge (e) = _____________________ C 1 Ex. Convert 9.6 x 10-19 J to eV. 9.6 x 10-19 J x ___________________ = ______________ eV Ex. Convert 4640 eV to J. 4640 eV x ___________________ = ___________________ J

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Conversions between units. See PhysRT, page ____: 1 electronvolt (eV) = _____________________ J Notice that this number is the same as the one in the conversion: 1 elementary charge (e) = _____________________ C 1 1.60 x 10-19 1.60 x 10-19 Ex. Convert 9.6 x 10-19 J to eV. 1 eV 1.60 x 10-19 J 6.0 9.6 x 10-19 J x ___________________ = ______________ eV Ex. Convert 4640 eV to J. 1.60 x 10-19 J 1 eV 7.42 x 10-16 4640 eV x ___________________ = ___________________ J

Summary of electric potential units: quantity big units small units W (or energy) q V J eV e C V V  eV's are NOT a unit of __________________________ . They are a unit for __________ or _____________. Also, you cannot mix: _____ with _______ or: _____ with _______ One of them must be converted first! potential difference energy work J e C eV

Ex. Find the work done in joules in moving 5 electrons through a potential difference of 6.0 V. Solution 1: Find answer in eV, then convert: V = W /q = = W ________ eV x _______________ = ____________ J Solution 2: Convert e to C first, then calculate. _______ e x __________________ = ____________ C 6.0 V W / 5 e 30 eV 1.60 x 10-19 J 1 eV 30 4.8 x 10-18 1.60 x 10-19 C 1 e 8.0 x 10-19 5 6.0 V 8.0 x 10-19 C W / 4.8 x 10-18 J

NOTES: Electric potential difference represents the ___________ per ____________ stored up in the system of charges. PE charge If the charges are allowed to move freely through a potential difference, they will gain the energy as _____ in the same way that a ___________ object gains it. KE falling gravity: electricity: PE = 100 J KE = 100 J PE = 100 J KE = 100 J