11.2 Electric Circuits: Analogies and Characteristics

(Pages 446-453)

Water circuit and electrical circuit analogy.

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.

Electric Circuits• Terminal: location on a cell (battery +/-)

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

Electric Circuits

Electrons Flow in One Direction in a Circuit

Electric Current

• Electric current: the rate of movement of electric charge

• Unit of charge à Coulomb (C)

• Unit of current à Ampere (A)

• Current measured using an ammeter

ELECTRIC CURRENT

• Electric current: the rate of movement of electric charge

“the amount of electron flow”

ELECTRIC CURRENT• Unit of charge à Coulomb (C)

ELECTRIC CURRENT• Unit of current à Ampere (A)

“AMPERE” à # of electrons moving per second

ELECTRIC CURRENT

• Current measured using an ammeter

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

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 300,000,000 m/s! Each individual electron, though, travels through the conductor at a muchslower pace. Actually, about only 0.1 mm/s.

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

CONFUSED? WATCH THIS..

Electrical Resistance

• Electrical resistance: the property of a substance that hinders electric current and converts electrical energy to other forms of energy (a bulb or load)

• Resistor: a device used in an electric circuit to decrease the current through a component by a specific amount

• Measured using an ohmmeter

Electrical Resistance

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

Potential Difference and the Volt

Electrical Cells and Voltage

VIDEO: The Flow of Electric Charge (and Electric Potential Difference)https://www.youtube.com/watch?v=7yOYSQ4YX-I

Practice

• Page 454 # 1-8