Voltage and Electric FieldContents:

• Voltage, work and charge• Voltage example• Whiteboards

• Voltage and electric field• Example• Whiteboards

• Electron Volts and accelerated ions

Voltage (AKA electric potential)

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Definition:V = Ep

qV = Change in Voltage (Volts)Ep = Change in potential energy (or work) (J)q = Charge (C)Example: Hans Full does .012 J of work on 630 C of charge. What is the change in voltage?

V = Ep/q = (.012 J)/(630x10-6C) = 19.05 J/C or 19 Volts or 19 V

Voltage is like pressureAir = 10,000 V/inShow

• Pickle-luminescence• Zap-O-Rama

Whiteboards: Voltage, Work and Charge

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10.0V W

V = Ep/q, Ep = 125 J, q = 12.5 CV = 10.0 V

Sandy Deck does 125 J of work on a 12.5 C charge. Through what voltage did she move it?

.600 J W

Lila Karug moves a 120. C charge through a voltage of 5000. V. How much work does she do?

V = Ep/q, q = 120x10-6 C, V = 5000. VEp = 0.600 J

13.8 mC W

Arthur Moore does 0.167 J of work moving an unknown charge through a voltage of 12.1 V. Please, please, won’t you please help him calculate the charge?

V = Ep/q, V = 12.1 V, Ep = 0.167 J

q = 0.013801653 = .0138 C = 13.8 mC

Voltage and distance and E Field

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Definition: (derive)E = -ΔV ΔxE = Electric FieldΔV = Voltage changeΔx = distance over which it changes(Why the minus sign)(Why I generally ignore it)

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Parallel Plates

Δx

What is the electric field when you have 12.0 V across two || plates that are separated by .0150 m?

E = ΔV/Δx = 12.0 V/.0150 m = 800. V/m. (show units)

E

Whiteboards: Voltage, Electric Field, and distance

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5.0x102 V/m W

E = -ΔV/Δx, ΔV = 25, Δx = .050 m, E = 500 V/m

Lei DerHosen places a voltage of 25 V across two || plates separated by 5.0 cm of distance. What is the electric field generated?

.39 V W

Art Zenkraftz measures a 125 V/m electric field between some || plates separated by 3.1 mm. What must be the voltage across them?

E = -ΔV/Δx, Δx = 3.1x10-3 m, E = 125 V/mΔV = 0.3875 V = 0.39 V

12 cm W

Oliver Goodguy needs to generate a 13 V/m electric field using a 1.50 V source. What distance should he separate || plates to generate this electric field?

E = -ΔV/Δx, ΔV = 1.50 V,, E = 13 V/mΔx = 0.1154 m = 0.12 m = 12 cm

43 V, bottom W

E = -ΔV/Δx, F = Eq, F = mgmg = Eq = ΔVq/ΔxV = 42.875 V = 43 VBottom positive

Carson Busses needs to suspend a 1.5 g (.0015 kg) pith ball against gravity. (gravity = electric) It has a charge of +12 C, and he is generating the electric field using plates that are 3.5 cm apart. What voltage should he use? Which side (top or bottom) is positive?

+Q

Accelerated ions

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Suppose we dropped a proton near the + 12 V side. What would be the proton’s velocity when it struck the right side?

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Wuall - Electric Potential Energy to kinetic

V = Ep/q, Ep = Vq = 1/2mv2

q = 1.602x10-19 C, m = 1.673x10-27 kg, V = 12 V

v = 47939 m/s = 48,000 m/s

0 V+12 V

Electron Volts

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1 electron volt is the energy of one electron charge moved through one volt.

An electron accelerated through 12 V has 12 eV of energy

1 eV = 1.602x10-19 J (Ep = Vq)

An alpha particle (2p2n) accelerated through 12 V has 24 eV of energy (two electron charges)

Whiteboards: Accelerated ions

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726,000 m/s W

V = Ep/q, Ep = Vq = 1/2mv2

V = 1.50 V, m = 9.11x10-31 kg, q = 1.602x10-19 Cv = 726327.8464 = 726,000 m/s

Brennan Dondahaus accelerates an electron (m = 9.11x10-31 kg) through a voltage of 1.50 V. What is its final speed assuming it started from rest?

1.81x10-17 J = 113 eV, it was accelerated through 113 V W

V = Ep/q, Ep = Vq = 1/2mv2

m = 1.673x10-27 kg, q = 1.602x10-19 C, v = 147,000 m/sEk = 1.81x10-17 J = 113 eV, it was accelerated through 113 V

Brynn Iton notices a proton going 147,000 m/s. What is its kinetic energy in Joules, through what potential was it accelerated from rest, and what is its kinetic energy in electron volts? (1 eV = 1.602x10-19 J, mp = 1.673 x 10-27 kg)

4.805x10-19 C which is 3e, so it is Fe+3 W

V = Ep/q, Ep = Vq = 1/2mv2 m = 9.287-26 kg, v = 7193 m/s, V = 5.00q = 4.805x10-19 C which is 3e, so it is Fe+3

Mark Meiwerds notices that Fe ions (m = 9.287x10-26 kg) are traveling 7193 m/s after accelerating from rest through 5.00 V. What is the charge on this ion, and is it Fe+1, +2, or +3?