INTRODUCTION TO ELECTRICITY Circuit Fundamentals

E LECTRICITY E LECTRICITY  Electricity: Current electricity is the flow of charged particles along a conductor.

C IRCUIT F UNDAMENTALS  To operate, an electrical device requires electrical energy, which is provided by a steady flow of charged particles along a closed loop.  This closed loop is called an electrical circuit.  The circuit must form a closed loop so that the charged particles charges moving through the conductorcan return to the battery.

C IRCUIT F UNDAMENTALS  A circuit contains:  a source of electrical energy, such as a battery  a conductor, such as a wire  a load that changes electrical energy into light, sound, heat, or motion

C IRCUIT F UNDAMENTALS

C URRENT A NALOGY  Highway 401 in the Toronto area is the busiest highway in North America.  If you were to stand beside the highway and count the cars as they passed, you would find that about cars pass by every hour —  that is about4.8 cars a second or over cars a day!

C URRENT  The amount of charge transferred per unit time is referred to as current.

C URRENT  Current is represented by the symbol I, and is measured in amperes (A).  Since current is the amount of charge that is transferred per unit time, the equation for current is:  where I is the current in amperes (A),  q is the amount of charge in coulombs (C),  and t is the time in seconds (s).

T YPES OF C URRENT  A steady flow of current in one direction, known as direct current, or DC.  Alternating current, or AC, changes direction periodically.  That is, the charges in the wire move back and forth over the same spot and do not actually move from one terminal to another.

T YPES OF C URRENT

R ESISTANCE A NALOGY  Highway 401 in the Toronto area is the busiest highway in North America.  If you were to close one lane all cars would have to use the same lane  There is less space so car must slow down

R ESISTANCE  Resistance is the degree to which the flow of current is opposed in a circuit.  A resistor is a device that resists or restricts the flow of current

E LECTRIC P OTENTIAL  Electrons repel each other. So when there is build up of charge the electrons will spread out.  If the electrons are held in one space this gives the electrons potential energy.  Much like a spring being squished

E LECTRIC P OTENTIAL  We define electrical potential as the electrical potential energy per unit charge.  Electrical potential is represented by the symbol V, and its units are volts (V).  It can be written mathematically as:

E LECTRIC P OTENTIAL A NALOGY Object Drop Demo  The higher the water the more POTENIAL ENERGY it has  Therefore there is more energy per kg for the water on top than on bottom  Therefore there is a Potential difference  5 J / Kg at the top  1 J / Kg at the bottom  Therefore potential difference is 4 J / Kg

P OTENTIAL D IFFERENCE  As charges pass through a load in the circuit, they transfer energy to the load.  This change in potential is referred to as the potential difference (V).

P OTENTIAL D IFFERENCE  Potential difference is also referred to as voltage.  The potential difference is always measured between two points in the circuit

P OTENTIAL D IFFERENCE A potential difference of 10.0 V is measured across a resistor in a circuit. If a charge of 20.0 C passes through the resistor, how much electrical energy is dissipated as heat?

C IRCUIT B ASICS