Warm Up

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Warm Up

• What color absorbs ALL colors of the visible
  light spectrum?
• What color reflects ALL colors of the visible
  light spectrum?
• Where does light travel fastest?
• Where does light travel slowest?
• We see different colors because objects reflect
  different _______________ of light.
• Amplitudes
• Wavelengths
• Speeds

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Series and Parallel Circuits
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resistance

• is the measure of how difficult it is for
  charges to flow through a material
• unit
• is the amount of charge that passes by a
  point in a second
• unit
• -the difference in electrical potential energy
  between 2 places in a circuit it is the energy
  that pushes charges through a circuit
• unit

Ohm (O)
current
Ampere, amp, A
voltage
volt, V
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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

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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

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• 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)

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• A switch is used to open and close a circuit.
• When the switch is open, electrical current
  CANNOT flow

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Brain Pop Electric Circuits
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Circuits

• Can either be series or parallel or a combination
  of the two.

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Series

• Current only takes one path for electrons
• Current flows through every part of the circuit

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Lights in a Series
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Series

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

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Adding Resistors to Series

• Current in the circuit will go DOWN (lights will
  dim)
• If you remove a light bulb or one burns outall
  go out!

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Resistance in Series

• Add up all resistors to get total resistance
• Total resistance will go up because all of the
  current must go through each resistor.

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Calculating Resistance Example

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

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Current in Series

• Current is the same at all points
• Use Ohms Law to find current using resistance
  and voltage

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Calculating Current Example

• If the resistances of loads R1, R2, and R3 are
  10O, 20O 30O respectively, and the voltage
  source is 6 V, what is the current through the
  circuit?

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Voltage in Series

• Voltage is reduced by each resistance voltage
  drop

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Calculating Voltage Example

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

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Sample Problem 1

• Draw a series circuit with two 1.5 V batteries, 3
  resistors, and a current of 0.5 A.
• What is the total voltage of the circuit?
• What is the resistance of each resistor?
• What is the voltage drop across each resistor?
  Label it on your circuit.

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Parallel Circuits

• Have at least one point where current divides
• More than one path for current to flow
• Paths are also known as branches

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Lights in Parallel
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Parallel

• If you add a resistor
• Total resistance goes down
• Total current goes up when you add another path

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Removing a Light Bulb

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

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Current in Parallel

• Current flows into a branching point, the same
  total current must flow out again
• Current depends on resistance in each branch

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Calculating Total Resistance in a Parallel Circuit

• Kirchoffs 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

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Current in Parallel

• Calculate current in each branch based on
  resistance in each branch by using Ohms Law

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Calculating Current Example

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

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Voltage in Parallel

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

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Calculating Voltage Example

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

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Practice problem 2

• Draw a parallel circuit with a 6 ohm a 18 ohm
  resistor (one on each branch) and a 12 V battery.
• What is the voltage through each resistor?
• What is the current flowing through each branch?

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Toll RoadCircuit Analogy
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Toll Booth Explanation

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

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Batteries in Series and Parallel
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• In seriesThe voltage is increased.
• In parallelNo change in voltage these batteries
  will last longer!

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One More FINAL Thing

• Two Types of Current
• DCDirect Currentproduced by solar cells and
  chemical cells (batteries)
• Current only flows in one direction.

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2nd type of current

• ACAlternating Current
• Current flows back and forth (alternates)
• Found in homes
• Generators produce AC current

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• 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

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• Generator converts mechanical to electrical
  energy
• Motor converts electrical to mechanical energy

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• When Andre plugs his stereo into the same outlet
  as the television and lamp, all three wont 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 stereos electrical cord was faulty.

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• 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 Sukis kitchen wired?
• A in a single loop
• B in a direct current circuit
• C in a parallel circuit
• D in a series circuit