Charging by Rubbing

+ -

+ Add + Charge

Charged Objects

Remove - Charge Add - Charge Remove + Charge

Simulation

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Electric Force

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Simulation

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-F e q 1

q 1

r

q 2

q 2

F e

F e

Coulomb’s Law F e = k q 1 q 2 / r 2 k = 9 x 10 9 Nm 2 /C 2 F e = k (1)(1)/ (1) 2 F e = k (1)(1)/ (2) 2 F e = k F e = ¼ k F e = k (2)(1)/ (1) 2 F e = k (2)(2)/ (1) 2 F e = 2k F e = 4k F e = k (2)(2)/ (2) 2 F e = k As r increases F e increases as the inverse square of r.

As q increases F e increases in direct proportion to q.

2 2 2 k

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 10 18 electron charges 6,250,000,000,000,000,000 electrons 6.25 quintillion electrons Electron charge = 1/6.25 x 10 18 coulombs Electron charge = 1.6 x 10 -19 coulombs Electron charge = .00000000000000000016 coulombs

Induced Charges

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

Simulation

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Grounding

100 25 0

75-

50 50 1 0 100-

Earth

99-

Aluminum Copper Gold Lead Nichrome Silver Steel Tungsten

Top 8 Conductors of Electricity The following metals are listed in alphabetical order. Arrange them in order of conductivity from best to worst.

1. Silver 1.47 x 10 -8 2. Copper 1.72 x 10 -8 3. Gold 2.44 x 10 -8 4. Aluminum 2.63 x 10 -8 5. Tungsten 5.51 x 10 -8 6. Steel 20 x 10 -8 7. Lead 22 x 10 -8 8. Nichrome 100 x 10 -8

I = Current measured in amperes. V = Voltage measured in volts.

R = Resistance measured in ohms.

Ohm’s Law Current = Voltage/Resistance I = V/R 1 amp = 1 volt/1 ohm

Electric Power Power = Current x Voltage P = I x V 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 = P t 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? # kwh = (P x t)/1000 #kwh = 600 x 30/1000 #kwh = 18 18 kwh x $.10 /kwh = $1.80

P = 600 watts t = 30 hours Cost = ? $

C A D

Electric Shock

What is the resistance of the human body?

If dry and insulated 500,000 Ώ If soaked in salt water 100 Ώ .001 amp .005 amp .010 amp .015 amp .070 amp B .10 amp can be felt is painful causes involuntary muscle contractions (spasms) causes loss of muscle control) If through the heart, serious disruption; probably fatal if current lasts for more than 1 second. Almost always fatal.

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?

I = V/R = 120/500,000 = .00012 amp Nothing.

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?

I = V/R = 120/100,000 = .0012 amp Shock felt.

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!

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Electric Circuit

R

1) Source of Voltage (Battery) 2) Device to convert energy (Resistor) 3) Complete conducting path (wires and switch)

Series Circuits

I = I

1

= I

2

= I

3

V = V

1

+ V

2

+ 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

V = V

1

= V

2

= V

3

I = I

1

+ I

2

+ I

3 Voltage is the same for all bulbs. The current in each bulb adds up to the total current from the Battery. If one bulb goes out, the others stay on.

Simulation Video