Transcript Electricity Slides

Charging by Rubbing
+
-
Charged Objects
Add + Charge
+
-
Remove - Charge
Add - Charge
Remove + Charge
Simulation
Electric Force
+
-
+
+
Simulation
Coulomb’s Law
Fe = k q1 q2/ r2
k = 9 x 109 Nm2/C2
Fe = k (1)(1)/ (1)2
-Fe
Fe
q1
q2
Fe = k (1)(1)/ (2)2
Fe = k (2)(1)/ (1)2
r
rr
11
q
q11
11
q
q22
11
F
Fee
kk
22
11
11
22
11
11
¼
¼ kk
2k
2k
11
22
22
4k
4k
2
2
2
k
Fe = k
Fe = ¼ k
Fe = 2k
Fe = k (2)(2)/ (1)2
Fe = 4k
Fe = k (2)(2)/ (2)2
Fe = k
As r increases Fe increases
as the inverse square of r.
As q increases Fe increases
in direct proportion to q.
The Unit of Charge
1 Coulomb is a very large amount of charge.
The unit comes from the definition of electric current.
1 ampere = 1 coulomb/second
1 coulomb = 6.25 x 1018 electron charges
6,250,000,000,000,000,000 electrons
6.25 quintillion electrons
Electron charge = 1/6.25 x 1018 coulombs
Electron charge = 1.6 x 10-19 coulombs
Electron charge = .00000000000000000016 coulombs
Induced Charges
-
+ + + + + + + + +
+
+
+
+ + + + + + + + +
-
+
+
+
+
+ + + + + + + + +
-
+
+
+
+ + + + + + + + +
Simulation
+ + +
+ + +
+ + +
Grounding
100-
50-
0
50-
75-
25-
99-
1-
0
100-
Earth
The following metals are listed
in alphabetical order. Arrange
them in order of conductivity
from best to worst.
Aluminum
Copper
Gold
Lead
Nichrome
Silver
Steel
Tungsten
Top 8 Conductors of Electricity
1.
2.
3.
4.
5.
6.
7.
8.
Silver
Copper
Gold
Aluminum
Tungsten
Steel
Lead
Nichrome
1.47 x 10-8
1.72 x 10-8
2.44 x 10-8
2.63 x 10-8
5.51 x 10-8
20 x 10-8
22 x 10-8
100 x 10-8
Ohm’s Law
Current = Voltage/Resistance
I = V/R
1 amp = 1 volt/1 ohm
I = Current measured in amperes.
V = Voltage measured in volts.
R = Resistance measured in ohms.
Electric Power
Power = Current x Voltage
P=IxV
1 watt = 1 amp x 1 volt
I = Current measured in amperes.
V = Voltage measured in volts.
P = Power measured in Watts.
Electric Power
Energy = (Power)(time)
E=Pt
You pay for electricity in kilowatthours (kwh)
1 kwh = (1000)(1J/s)(3,600s) = 3,600,000 J
Cost per kwh = $.10 (approximately)
Electric Power (cont)
A 600 watt hair dryer is
operated for 1 hour per
day for 30 days. If the
electric company charges
$.10 per kilo-watt-hour,
what is the cost to operate
the dryer?
P = 600 watts
t = 30 hours
Cost = ? $
# kwh = (P x t)/1000
#kwh = 600 x 30/1000
#kwh = 18
18 kwh x $.10 /kwh = $1.80
Electric Shock
A
C
D
What is the resistance of the human body?
If dry and insulated
500,000 Ώ
If soaked in salt water
100 Ώ
B
.001 amp
.005 amp
can be felt
.010 amp
is painful
causes involuntary muscle contractions (spasms)
.015 amp
causes loss of muscle control)
.070 amp
If through the heart, serious disruption; probably fatal
if current lasts for more than 1 second.
Almost always fatal.
.10 amp
Electric Shock (cont.)
What are the effects of electric shock?
1. Muscle contractions and spasms.
2. Heating and burning.
A dry person standing on a wood floor has a resistance of 500,000 Ώ.
He comes in contact with a 120 volt “hot” electric wire. What happens?
= .00012 amp
Nothing.
I = V/R
= 120/500,000
A dry person standing on a concrete floor has a resistance of 100,000 Ώ.
He comes in contact with a 120 volt “hot” electric wire. What happens?
= .0012 amp
Shock felt.
I = V/R
= 120/100,000
A wet swimmer standing on a concrete floor has a resistance of 500 Ώ.
He comes in contact with a 120 volt “hot” electric wire. What happens?
I = V/R
= 120/500
= .24 amp
Death!
Electric Circuit
R
+
V
-
1) Source of Voltage (Battery)
2) Device to convert energy (Resistor)
3) Complete conducting path (wires and switch)
Series
Circuits
I = I 1 = I2 = I3
V = V 1 + V2 + V 3
Current is the same for all bulbs.
The voltage across each bulb adds up
to the total voltage of the battery.
If one bulb goes out, they all go out.
Simulation
Parallel Circuits
Voltage is the same for all bulbs.
V = V1 = V 2 = V 3
The current in each bulb adds up to
I = I 1 + I2 + I 3
the total current from the Battery.
If one bulb goes out, the others stay on.
Simulation
Video