1. 11.2 Electric Circuits: Analogies and Characteristics (Pages 446-453)
Water circuit and electrical circuit analogy.

2. Learning Goals
I can describe how electric current moves through circuits.
I can explain what current, voltage and resistance are, and how these quantities are measured.

3. An electric circuit is a closed path along
which electrons powered by energy source
can flow.
In a circuit that is connected to a cell,
Electrons move very slowly from the
negative terminal to the positive terminal
in the external circuit.
The electric field in an operating circuit
transmits energy at almost the speed
of light.

4. Electric current is the rate of flow of electric charge in a circuit, and it is measured in Amperes (A) using an ammeter.
Electrical resistance is a property of a substance that hinders electric current and converts electrical energy to other forms of energy.
Potential difference (voltage) is the difference between the electric potential energy per unit of charge at two points in a circuit, and it is measured in Volts (V) using a voltmeter.

5. There is a positive terminal & a negative terminal.
Electric circuits:
What is an electric circuit?
An electric circuit is a closed path along which electrons that are powered by an energy source can flow.
What are the 2 types of terminals?
There is a positive terminal & a negative terminal.
Is a switch essential for a circuit to operate?
No, a switch is not essential for a circuit to operate, but it is included for convenience.
What are the most popular connecting wires being used to make an electrical circuit?
The most popular wire is copper metal covered with an insulator made of plastic or rubber.

6. Distinguish between a closed and open circuits?
An open circuit is one in which there is a gap or break in the circuit. A closed circuit has no gaps and allows electrons to flow from and return to an energy source.
Movement of Electrons:
Describe the movement of electrons in a circuit.
The electric field produced by the cell travels at almost the speed of light and forces the free electrons to move, overall, in one direction, although there may be collisions among the electrons. The movement of the electrons is from the negative terminal to positive terminal

7. Electric Circuits
Terminal: location on a cell that must be connected to other components to form a circuit
Switch: a control device that can complete or break the circuit to which it is connected
Open circuit: a circuit that contains a gap or break

8. Electric Circuits

9. Electrons Flow in One Direction in a Circuit

10. As each electron moves uniformly through a conductor, it pushes on the one ahead of it, such that all the electrons move together as a group. The starting and stopping of electron flow through the length of a conductive path is virtually instantaneous from one end of a conductor to the other, even though the motion of each electron may be very slow. An approximate analogy is that of a tube filled end-to- end with marbles:
If a single marble is suddenly inserted into this full tube on the left-hand side, another marble will immediately try to exit the tube on the right. Even though each marble only traveled a short distance, the transfer of motion through the tube is virtually instantaneous from the left end to the right end, no matter how long the tube is. With electricity, the overall effect from one end of a conductor to the other happens at the speed of light: a swift 186,000 miles per second!!! Each individual electron, though, travels through the conductor at a much slower pace. Actually, about only 0.1 mm/s.

11. Electrons Flow in One Direction in a Circuit:
Describe the flow of electrons when a conductor is not connected and when a circuit is connected.
If a conductor is not connected, the electrons move in random directions, frequently colliding with other electrons or with ions.
The instant a circuit is completed, the electric field causes the electrons to move in one direction through the wire.

12. Electric Current
Electric current: the rate of movement of electric charge
Unit of charge  Coulomb (C) the quantity of charge that is equal to the charge of 6.25 × 1018 electrons
Unit of current  Ampere (A) the unit of electric current, equivalent to one coulomb per second
Measured using an ammeter

13. Electric Fields, Circuits and Curents
Separation of charges between two electrodes in a cell gives rise to an electric field
This field transmits an electric force (and current) through a circuit at almost the speed of light
Electrons flow slowly

14. Conventional Current vs. Electron Flow
Electrical engineers often describe the direction of electric current as the direction in which a positive charge would move
Either method is acceptable, as long as it is used consistently

15. Electrical Resistance
Electrical resistance: the property of a substance that hinders electric current and converts electrical energy to other forms of energy
Resistor: a device used in an electric circuit to decrease the current through a component by a specific amount
Measured using an ohmmeter

16. Electrical Resistance

17. A load is a resistor or any other device that transforms electrical energy into heat, sound, motion or light. Examples of loads are resistors, motors, speakers & light bulbs.

18. Water circuit and electrical circuit analogy.
Potential Difference:
Compare and contrast a water tap in your home and an electric switch. A tap acts to allow or prevent water
from flowing. It acts much like an
electric switch, which allows or
prevents electricity from flowing.
A tap can also change the amount or
flow of water flowing. Most electric switches
cannot do this, except for dimmer switches.
Water circuit and electrical circuit analogy.

19. Potential Difference and the Volt
Potential difference (voltage): the difference between the electric potential energy per unit of charge at two points in a circuit
Volt: the unit for potential difference, equivalent to one joule (J) per coulomb (C)
Measured using a voltmeter

20. Potential Difference and the Volt

21. Electrical Cells and Voltage

22. Practice
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