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Transcript of CURRENT ELECTRICITY
What is Electricity?
Electric charges that move...specifically electrons!
Are moved by attraction FORCE of an opposite charge
This FORCE acts at a distance...like magnets
Electrons are pushed and pulled through a circuit by a difference in charge...VOLTAGE
When they move this is called CURRENT!
The path these electrons take must be COMPLETE
This measures the amount of electrons that move through a CONDUCTOR in a given second.
It involves a continues flow of electrons much like water down a river.
This differs from lightning b/c it is a CONTINUOUS flow, unlike lightning.
Conductors are materials that allow electrons to flow b/c they have a weak attraction for their electrons.
What kinds of materials fit this description? .....
Use what you know about atoms to help
How is Current Measured?
Number of electrons (measured in coulombs) that pass a point in a given second.
1 Coulomb of electrons= 6.2415 × 10^18 electrons
1C/s = 1 Amp of current so...
20 coulombs of electrons moving through a circuit in one second = 20 amps
Each electron has a charge that it carries..therefore 20amps is A LOT of energy
Examples of Conductors:
Examples of Insulators:
Have a strong attraction to their electrons by the molecules nucleus and don't allow electrons to move.
Can you think of examples?
For electrons to move CONTINUOUSLY there must be a complete "loop" for which they can pass
ANY breaks in the path makes the circuit incomplete/ impassable
Without a "complete circuit" electrons will not flow
-Remember the path must consist of conductors!
complete path using conducting material
potential difference (voltage source)
Resistor (something to use the energy)
Electrons are moved by electric fields around charges
Creating a difference in charge/energy on one end of a circuit versus the other causes charges to move
Opposite charges attract ...positive towards negative
Like charges repel (+ to +
- to -)
When there is a difference in energy between two points objects move from high PE to low PE decreasing the PE.
To get things to move from low PE to high PE, work (which requires energy) must be done to increase the PE
MORE CHARGE = MORE ENERGY NEEDED = MORE ELECTRICAL POTENTIAL ENERGY
Example: The greater the mass of an object the more work is necessary to move the object against gravity
How Does Electrical Potential Work in Circuits?
Charge moves from High PE (+) to Low PE (-)
For charges to CONTINUE to move work/energy must be done on the charge to move back from Low PE to High PE
The difference in energy is created by the battery
Potential Difference = Voltage
Difference in P.E. between ends of circuit
Circuits are like water park slides...
Created by the battery between terminals
Measured in volts
High P.E - Low P.E = Voltage Drop
use <, >, or = between each below
Electrons don't travel fast....they are actually very slow...it's just there are A LOT of them
Think about it...
One atom of copper has 29 electrons... in a .01 cm piece of copper wire there are about 3.51 x 10^20 atoms of copper...if only 1 electron moved there would be 56 coulombs of charge!!!!
Why do the lights turn on so quickly if electrons move so slowly (1m per hour)??
a. When an electrochemical cell no longer works, it is out of charge and must be recharged before it can be used again.
b. An electrochemical cell can be a source of charge in a circuit. The charge that flows through the circuit originates in the cell.
c. Charge becomes used up as it flows through a circuit. The amount of charge that exits a light bulb is less than the amount that enters the light bulb.
d. Charge flows through circuits at very high speeds. This explains why the light bulb turns on immediately after the wall switch is flipped.
e. The local electrical utility company supplies millions and millions of electrons to our homes everyday.
T or F....
Resistance is the hindrance to the flow of charge.
Factors that affect resistance include:
Length of conducting material
Think about water flowing through pipes....
Relates Voltage (V), Current (I), and Resistance (R)
What does this mean....
as voltage increases current increases
as resistance increases current decreases
Can be used to solve for V or R as well
A complete circuit with only ONE path for electrons to travel
Electrons must travel through EVERY resistor to complete the circuit.
Causes each resistor in the circuit to SHARE voltage
Each resistor added causes current to decrease
Circuits made of MULTIPLE paths for electrons to travel
Electrons DO NOT have to pass through each resistor
Each resistor added in parallel is on its own path from the voltage source.
Each "path" added increases current
Voltage drop depends on the resistor