Download 05-01VoltageandElectricField

Voltage and Electric Field
Contents:
•Voltage, work and charge
•Voltage example
•Whiteboards
•Voltage and electric field
•Example
•Whiteboards
•Electron Volts and accelerated ions
Voltage (AKA electric potential)
Voltage is like pressure
Air = 10,000 V/in
Show
•Pickle-luminescence
•Zap-O-Rama
Definition:
V = Ep
q
V = 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
TOC
Whiteboards:
Voltage, Work and Charge
1|2|3
TOC
Sandy Deck does 125 J of work on a
12.5 C charge. Through what voltage
did she move it?
V = Ep/q, Ep = 125 J, q = 12.5 C
V = 10.0 V
10.0V
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. V
Ep = 0.600 J
.600 J
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
13.8 mC
W
Voltage and distance and E Field
Definition: (derive)
E = -ΔV
Δx
E = Electric Field
ΔV = Voltage change
Δx = distance over which
it changes
(Why the minus sign)
(Why I generally ignore it)
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
Δx
-
Parallel Plates
TOC
Whiteboards:
Voltage, Electric Field, and distance
1|2|3|4
TOC
Lei DerHosen places a voltage of 25 V
across two || plates separated by 5.0
cm of distance. What is the electric
field generated?
E = -ΔV/Δx, ΔV = 25, Δx = .050 m,
E = 500 V/m
5.0x102 V/m
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/m
ΔV = 0.3875 V = 0.39 V
.39 V
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/m
Δx = 0.1154 m = 0.12 m = 12 cm
12 cm
W
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?
E = -ΔV/Δx, F = Eq, F = mg
mg = Eq = ΔVq/Δx
V = 42.875 V = 43 V
Bottom positive
43 V, bottom
+Q
W
Accelerated ions
Suppose we dropped a proton near the
+ 12 V side. What would be the
proton’s velocity when it struck the
right side?
0V
+12 V
+
+
+
+
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
TOC
Electron Volts
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)
TOC
Whiteboards:
Accelerated ions
1|2|3
TOC
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?
V = Ep/q, Ep = Vq = 1/2mv2
V = 1.50 V, m = 9.11x10-31 kg, q = 1.602x10-19 C
v = 726327.8464 = 726,000 m/s
726,000 m/s
W
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)
V = Ep/q, Ep = Vq = 1/2mv2
m = 1.673x10-27 kg, q = 1.602x10-19 C, v = 147,000 m/s
Ek = 1.81x10-17 J = 113 eV, it was accelerated through 113
V
1.81x10-17 J = 113 eV, it was accelerated through 113 V
W
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?
V = Ep/q, Ep = Vq = 1/2mv2
m = 9.287-26 kg, v = 7193 m/s, V = 5.00
q = 4.805x10-19 C which is 3e, so it is Fe+3
4.805x10-19 C which is 3e, so it is Fe+3
W