Warm Up1. What color absorbs ALL colors of the visible

light spectrum?

2. What color reflects ALL colors of the visible light spectrum?

3. Where does light travel fastest?

4. Where does light travel slowest?

5. We see different colors because objects reflect different _______________ of light.

a) Amplitudes b) Wavelengthsc) Speeds

Series and Parallel Circuits

is the measure of how difficult it is for charges to flow through a materialunit:

is the amount of charge that passes by a point in a secondunit:

-the difference in electrical potential energy between 2 places in a circuit; it is the energy that pushes charges through a circuit unit:

resistance

Ohm (Ω)

current

Ampere, amp, Avoltage

volt, V

Objectives• Name the three essential parts of a

circuit.

• Compare series circuits with parallel circuits.

• Explain how fuses and circuit breakers protect your home against short circuits and circuit overloads.

Compare motors and generators

Electric Circuits

• An electric circuit is a complete, closed path through which electric charges flow.

• All circuits have three basic parts:• Energy source• Wires• Load

• Energy source examples:• Battery• Generator• power plant (coal, nuclear, gas)• hydroelectric plant

• Loads change electrical energy to other forms of energy

• Examples: lightbulb, television, toaster

• Wires are made from conductive materials (i.e., copper)

A switch is used to open and close a circuit. When the switch is open, electrical

current CANNOT flow

Brain Pop: Electric Circuits

CircuitsCan either be series or

parallel or a combination of the two.

SeriesCurrent only takes one path for electrons

Current flows through every part of the circuit

Lights in a Series

SeriesIf you add a resistor (like another light):Total resistance goes UP since all the current has must go through each resistor.

Adding Resistors to Series:Current in the circuit will go DOWN (lights will dim)

If you remove a light bulb or one burns out—all go out!

Resistance in SeriesAdd up all resistors to get total resistance Total resistance will go up because all of the current must go through each resistor.

Calculating Resistance Example:

If the resistances of loads R1, R2, and R3 are 10Ω, 20Ω & 30Ω respectively, what is the total resistance in the circuit?

Current in Series

Current is the same at all points

Use Ohm’s Law to find current using resistance and voltage

Calculating Current Example:If the resistances of loads R1, R2, and R3 are 10Ω, 20Ω & 30Ω respectively, and the voltage source is 6 V, what is the current through the circuit?

Voltage in Series

Voltage is reduced by each resistance – voltage drop

Calculating Voltage Example Using the current

that you calculated in the previous problem, what is the voltage difference (drop) across each resistor?

Sample Problem #1 Draw a series circuit with two 1.5 V

batteries, 3 resistors, and a current of 0.5 A.

1. What is the total voltage of the circuit?

2. What is the resistance of each resistor?

3. What is the voltage drop across each resistor? Label it on your circuit.

Parallel CircuitsHave at least one point where current divides

More than one path for current to flow

Paths are also known as branches

Lights in Parallel

Parallel:If you add a resistor:

Total resistance goes down

Total current goes up when you add another path

Removing a Light BulbIf you remove a light bulb or one burns out, the others stay on because the circuit is still closed.

Current in Parallel Current flows into a branching point, the same total current must flow out again

Current depends on resistance in each branch

Calculating Total Resistance in a Parallel Circuit

Kirchoff’s Law of Currents states that the sum of the currents in must equal the sum of the currents out.

The formula for calculating total Resistance, RT:

Current in ParallelCalculate current in each branch based on resistance in each branch by using Ohm’s Law

Calculating Current Example: If the resistances of

loads R1, R2, and R3 are 10Ω, 20Ω & 30Ω respectively, what is the total resistance in the circuit?

Voltage in Parallel

Voltage is the same across each branch – because each branch is on the same wire

Calculating Voltage Example: If the voltage

source is 6 V, what is the voltage difference (drop) across each resistor?

Practice problem #2

Draw a parallel circuit with a 6 ohm & a 18 ohm resistor (one on each branch) and a 12 V battery.

1. What is the voltage through each resistor?

2. What is the current flowing through each branch?

Toll Road—Circuit Analogy

Toll Booth ExplanationAdding toll booths in series

increases resistance and slows the current flow.

Adding toll booths in parallel lowers resistance and increases the current flow.

Batteries in Series and Parallel:

In series—The voltage is increased.

In parallel—No change in voltage; these batteries will last longer!

One More FINAL Thing:

Two Types of Current:DC—Direct Current—produced by solar cells and chemical cells (batteries)

Current only flows in one direction.

2nd type of current:AC—Alternating CurrentCurrent flows back and forth (alternates)

Found in homesGenerators produce AC current

Too many loads or too much voltage can be dangerous fuse -thin strip of metal that melts

and opens circuit

circuit breaker – sometimes a piece of metal that bends, thus opening the circuit

Generator – converts mechanical to electrical energy

Motor – converts electrical to mechanical energy

When Andre plugs his stereo into the same outlet as the television and lamp, all three won’t work. What is the most likely hypothesis for what happened?

A The circuit was overloaded, and the circuit breaker opened.

B The circuit was complete, and the circuit breaker closed.

C Only the stereo operates on alternating current.

D The stereo’s electrical cord was faulty.

Suki can have all five appliances in her kitchen on at the same time, or she can have each appliance on one at a time. How are the appliances in Suki’s kitchen wired?

A in a single loop

B in a direct current circuit

C in a parallel circuit

D in a series circuit