ELECTRICITY

ELECTRICITY

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What do you already know about it?Voltage?

Resistance?Current?

Do Smarty Demo

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 Electric Circuit A path over which electrons travel, out through the negative terminal, through the conductor, back in through the positive terminal.

http://www.stmary.ws/highschool/physics/home/notes/electricity/circuits/Conductivity.htm

http://www.stmary.ws/highschool/physics/home/notes/electricity/circuits/Conductivity.htm

http://www.youtube.com/watch?v=0oTmAP_EESI&feature=player_embedded

Electric Current

Alternating Current and Direct Current

191.60 101

CoulombsElectron

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11.60 10

ElectronCoulombs

If a single electron has a charge of 1.60 × 10-19 Coulombs, then

Now flip to get the number of electrons in 1 coulomb of charge

186.24 10 ElectronCoulombs

A collection of 6.24 × 1018 electrons has a charge of one Coulomb

Electric current is the flow of electrons through a wire. Measured in Amperes (A).

1 Amp is 1 coulomb of charge per second.

That means that 6.24 × 1018 electrons flow past any single point in the circuit.

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qIt

Current is the amount of charge flowing through a circuit in a set amount of time then the formula for current would be

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Example:A battery can deliver 14.7 coulombs of charge in

30 s. Find the current.

14.7 0.4930

q CI At s

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Voltage can be thought of as, “The driving force which causes the current to flow”

Current flows from high electric potential to low electric potential.

Just like a ball will roll down a hill in an attempt to shed off its gravitational potential energy, an electron will flow towards a proton to shed off its electrical potential energy.

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Electric Potential - work needed or energy acquired when a positive charge is moved from infinity to a certain point in an electric field.

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Potential Difference – The change in the potential energy of a charge as it is moved between 2 points within an electric field.

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The difference in this electric potential energy is what is known as voltage

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JouleVoltCoulomb

1 Volt is when a battery cell provides 1 Joule of electrical potential energy to each coulomb of charge as it moves through the cell.

Current does not flow unless there’s a potential difference (voltage) present.

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In a battery the potential difference (voltage) between the positive and negative terminals sets up an electric field.

This electric field causes electrons to accelerate in the direction of the positive terminal thus causing current to flow.

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If "Opposites" move closer they gain Kinetic Energy They speed up

As a charge moves through an electric field it gains either Potential Energy or Kinetic Energy

If 'Opposites' separate they gain Potential Energy

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If "Likes" separate they gain Kinetic Energy

If "Likes" move closer they gain Potential Energy

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If an amount of Energy is supplied to charge as it moves between 2 points there is an electrical potential difference between the points. 

V = Potential Difference (V) E = Energy (Joules)

q = Charge (Coulombs)

EVq

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Example: If a battery cell provides 3.0 J of electrical

potential energy in moving 2 coulombs of charge through the cell, what is the potential difference (or voltage) of the cell?

3.0

1.52.0 Coulombs

JoulesEV Voltsq

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Example:

W E

It takes 6 Joules of work to move 2 coulombs of charge between 2 points in an electric field. What is the potential energy difference (voltage) between these 2 points?

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32 Coulombs

JoulesE WV Voltsq q

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ResistanceAs electrons move through a material they experience collisions with other atoms.

These collisions cause energy to be given off in the form of heat and can be thought of as a type of resistance to the movement of the electrons.

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Electrical resistance is the “friction”

of the electrical world*

Electrical resistance is measured in ohms ()

Electrical resistance is when a material resists or does not allow current to flow through the material.

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Resistance Depends on 4 Factors:

2.    Length of MaterialIncreasing the length of the material causes an increase in the number of collisions, which in turn increases the resistance .

1.    Temperature Increasing the temperature causes an increase in the collision of particles, which then in turn increases the resistance. 

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3.    Cross Sectional Area of WireIncreasing the space, decreases the number of collisions, which then decreases the resistance.

4.       Nature of the MaterialMetals differ in both the number of the free electrons and the space available for electron movement.

The number that indicates the resistance of materials per meter in length of 1m2 cross-sectional area, at a given temperature, is called resistivity of the material.

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Insulators have very high values of resistivity whereas good conductors have very low resistivities.

Resistors are materials with a mid-range resistivity.

Resistance

http://www.youtube.com/watch?v=WzUTOeoxREM&feature=related

http://www.stmary.ws/highschool/physics/home/notes/electricity/intro/wiresResistanceCurrent.swf

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Ohms Law The potential difference across a load

equals the product of the current through the load and the resistance of the load.

V = IR

R = Resistance (Ohms ) V = Potential Difference (Volts V)

I = Current (Amperes A)

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A 120 Volt potential difference applied to the terminals of a light bulb produces a 2.2 A current through the bulb. Calculate the resistance of the light bulb.

Example:

120 552.2

VRI

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Electrical Power: The rate at which electric energy is

converted to other forms of energy is called the power output in the circuit.

  P = Power in J/s (Watts) E = Energy in J

t = time in seconds

EPt

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We can use unit analysis to put the equation for power in to a different form as well.  

Since Volts are J/C and Amps are C/s.

J C JC s s

Therefore: (P=VI) must also be true.

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Example:Find the power consumed by the light bulb in the following circuit.

P = VI = 1.5 0.1 = 0.15 W

Electricity

http://www.stmary.ws/highschool/physics/home/notes/electricity/circuits/ResistanceWire.htm

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Pg. 692 #’s 1, 2

Homework

Pg. 696 #’s 4, 6Pg. 714 #’s 21, 23Pg. 737 #’s 40, 41, 42RRHS Handout