Download Physical Science Unit 9 * Electricity and Magnetism

Physical Science Unit 7 – Electricity and Magnetism
Chapters 20 and 21
I.
Electrons and Electron Flow
A. Atomic Structure
B. Electric Forces - Loss or Gain of Electrons
C. Electron Flow
II.
Static Electric Charge
How Occurs
Same/Opp Charge
Repel/Attract
Friction
Induction
Conduction
III.
Electric Circuits (Circuit Lab, Resistance Lab)
A. Closed Circuit
B. Open Circuit
C. Symbols
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D. Series Circuit
1.
Diagram
2.
Resistance Increased
3.
Effect on Current Flow
4.
Removing a Resistor
5.
Increasing Voltage of Battery
2
E. Parallel Circuit
1. Diagram
2. Resistance Reduced
3. Effect on Current Flow
4. Removing a Resistor
6.
IV.
Increasing Life of Battery
Ohm’s Law
V = IR
A. Voltage
1.
2.
Definition
Unit
B. Resistance
1. Definition
2.
Unit
3.
Affected by Diameter, Length of Wire
C. Current
1.
Definition
3
2.
Unit
3.
Direct Current (DC)
a.
4.
V.
Batteries
Alternating Current (AC)
a. Generator
Electromagnetism (Electrical Energy to Magnetic Energy)
A. Magnetic Fields
B. Current Flow and Magnetic Fields
C. Electromagnets (Electrical Energy to Magnetic Energy)
1.
# of Coils
2.
Core
3.
Amperage
D. Simple Motors (Electrical Energy to Magnetic Energy to Mechanical Energy)
E. Generators (Mechanical Energy to Magnetic Energy to Electrical Energy)
1. Creating Alternating Current
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5
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principles of Electrical Circuits
An electrical circuit is a flow of electrons. A circuit is the path along which the electric current flows. The electrons
will only flow when a circuit is complete. When a circuit is complete, electrons will flow from the negative terminal
of a power source through the circuit and return to the same source through the positive terminal. A flashlight dry cell
is a common source of electrical power.
If a complete circuit is made by connecting the two terminals with a wire, the electrons will flow from the
negative to the positive terminal. When this pathway exists we say we have a complete circuit or a closed
circuit. If there is a break in the pathway we call it an open circuit.
An electric bulb will not light unless the electricity flows through it. The two terminals of the bulb are shown
in the drawing below. The electrons can enter either terminal and leave through the other one.
The bulb gives light because the flow of electricity makes the wire filament inside the bulb get hot. Enough
heat is produced to make the bulb incandescent. Resistance, a kind of “electrical friction” caused by the
electrons moving through the filament heats it. The filament will not glow when the circuit is incomplete. The
most common type of failure in electrical bulbs occurs when the filament melts or breaks.
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To check what you have learned about electrical circuits, study each question and diagram. Then,
decide upon an answer.
If we take two 1.5 volt flashlight dry cells, a switch, wire, and a flashlight bulb we can make a type of
flashlight.
1. Will the bulb glow if the parts are connected as shown below? Explain.
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2. What will happen if the circuit is wired as shown here? Explain
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3. Will the bulb glow when the circuit is connected this way? Explain.
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4. What will happen if the circuit is wired in this way? Explain.
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5. What would happen if the circuit is wired this way? Explain.
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6. What would happen if the circuit is wired this way? Explain.
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7. What would happen if the circuit is wired in this manner? Explain.
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8. If the wiring is connected this way, what will happen? Explain.
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9. Draw a circuit diagram using electrical symbols of circuit #8. Then add a switch. What will happen if
another dry cell (battery) is added to the circuit?
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Parallel vs. Series Circuits
Name ___________________
Directions: Create two simple circuits using the items in the zip lock bags.
Draw the sketch of your circuit in the space below for the correct circuit
Series
Parallel
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Circuit Circus
Purpose: Compare the functioning of simple series and parallel circuits. Complete this in your notebook.
Materials:
Dry cells (size D), copper wire, bulbs
Procedure:
Part I
1. Using only the D cell battery, the copper wire and the flashlight bulb, arrange them in as many ways
as you can to make the bulb light.
2. Make a sketch of each set-up in your notebook. Include sketches of failures as well as successes.
3. In your own words, describe the similarities between your successful trials.
Part II
1. Using one battery, light as many bulbs as you can. Keep track of your trials through your sketches.
2. Using two batteries, light as many bulbs as you can. Again keep track of your various arrangements of materia
3. Using three bulbs and two batteries, discover the arrangements that give different degrees of bulb brightness. K
record of your trials.
Questions:
1. How did you make the most bulbs glow using only one battery? Compare your results with the class.
2. What set-up lit the most lights when you used two batteries? Compare results with the class.
3. How many different degrees of brightness did you obtain using three bulbs and two batteries? Compare results
the class.
4. How many different ways can you connect bulbs and batteries and still have a working circuit?
Part III
1. Connect the materials as shown in the circuit diagrams. The bulbs are connected in series.
2. Using the second diagram, unscrew one of the bulbs. What happened?
3. Now set up the materials as shown in the following diagram. The bulbs are connected in parallel.
4. Unscrew one of the bulbs. What happened?
5. Build a series circuit using two batteries and one bulb. Sketch your circuit.
6. In your own words describe the differences between series and parallel circuits.
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Circuit Lab II
Comparing Series and Parallel Circuits
Background:
1. Explain the difference between a parallel and a series circuit.
Include circuit diagrams in your explanation.
2. What is the purpose of switches in circuits?
3. What is the purpose of circuit breakers in circuits?
4. Predict the effects of removing a light bulb from a series and a parallel circuit.
5. Predict the effects of adding a light bulb to a series and a parallel circuit.
Safety: Some parts of circuits can become hot. Do not leave the battery connected or the
circuit closed for more than a few seconds at a time. Never
connect the positive and negative terminals of the battery directly
without including at least one light bulb.
Procedure to Construct Series Circuit: Attach two batteries
and three lights to one another in a large circle using the
materials in your electricity kit.
Data and Observations: Include sketches for all of your circuits.
- Record observations about the brightness of the 3 lights.
- Remove the middle bulb without adjusting the connection
and record observations.
- Add a bulb (4 total) and record observations.
- Remove the final bulb and record observations.
Questions:
1. What will happen in a series circuit if one light bulb is
added?
2. What will happen in a series circuit if one light bulb is removed from the end?
3. What will happen in a series circuit if a light bulb within the circuit is removed?
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4. Explain the results of 1 and 2 above in terms of electron flow.
Procedure to Construct a Parallel Circuit: Place two strips of aluminum foil parallel to one
another a few centimeters apart on the desk. Place three lights in the middle and tape the
exposed wires to the strips of aluminum foil. Connect the battery to the aluminum foil using
paperclips.
Data and Observations: Include sketches for all of your circuits.
- Record observations about the brightness of the lights.
- Remove a bulb from the middle without adjusting the connection and record
observations.
- Add a bulb (4 total) and record observations.
- Remove the last bulb and record observations.
Questions:
1. What will happen in a parallel circuit if one light bulb is added?
2. What will happen in a parallel circuit if one light bulb is removed from the end?
3. What will happen in a parallel circuit if a light bulb within the circuit is removed?
4. Explain the results of 1 and 2 above in terms of electron flow.
Conclusion:
1. Compare the brightness of the lights in series vs. parallel circuits as you add or remove
bulbs. Explain why the two circuits shine differently.
2. What happens in the two circuits if you remove the middle bulb? Explain in terms of
electron flow.
3. Which type of circuit would be used when building houses and why?
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Van Der Graf Demo Directions: For each demonstration please write:
1. A prediction of what will happen.
2. What happens and why.
1. How to make a lightening bolt
2. Balloon
3. Pie Pans
4. Packing Peanuts
5. Coffee Filter
6. Plastic vs. Glass Bottle
7. Grits
8. Thumb tack
9. Human Chain
10. Light bulbs
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Electric Math
In electrical circuits, there are three basic variables. The relationship between these three variables
is called Ohm’s Law, V=IR. Complete the chart and triangle below to show the symbol, meaning, and units
for each of these variables.
Variable
Symbol
(used in
formulas)
Meaning
Unit
Voltage
Current
Resistance
1. If there is a 22 ohm resistance in the heating element of a coffee maker and it is plugged into a 110
volt outlet, how much current will pass through it?
Step 1:
Step 2:
Step 3:
R=
V=
I=
2. A typical lamp operates at about 115 volts with a current of 0.25 amps. What is the resistance of the
lamp?
3.
What voltage would be needed to produce a 2.5 amp current running to a hot tub with an internal
resistance of 88 ohms?
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Ohms Law Lab
Name: _________________
In this activity you will use gravitational potential energy and water to model potential difference and
current in an electrical circuit
Materials:
Funnels, ring stand, clip, 2 beakers, ruler
Procedure:
1. Measure the height from the top of the funnel to the bottom of the glass beaker, record in data table.
2. Pour 200 ml of water into the funnel fast enough to keep it full but not overflowing
3. Measure the time it takes 100 ml of water to flow into the lower beaker, record
4. Repeat the experiment 3 times for each of the three beakers
Data Table:
Funnel
1
trial (.1 L)
Height (m)
time (s)
Rate (L/s)
1
______
______
2
3
avg
2
______
______
1
2
3
avg
3
_______
1
_________
3
2
avg
Conclusion Questions:
1. Gravity causes water to move can be compared to voltage. Which funnel allows for the highest
voltage?
2. The rate L/s of the flow of the water is compared to the current, which trial represents the highest
current?
3. If the voltage is increased what happens to the current?
4. According to ohms law, what should happen to the current if the voltage stays the same but the
resistance is reduced?
5. If a long funnel has more resistance, what should happen to the rate of flow if the tube is made
shorter?
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Directions: Identify each as a conductor or an insulator by putting a c or an i in the blank
metal doorknob ____
gold ____
copper ___
plastic ____
carpet ___
wood _____
bulletin board ____
metal coat hanger ____
silver ____
rubber ____
clothing ____
paper clip ____
Directions: Underline the term in parentheses that makes each statement true.
1. A negatively charged object has (more, fewer) electrons than one that is neutral.
2. Electrons flow from areas of (higher, lower) voltage to areas of (higher, lower) voltage.
3. Voltage difference is measured in (amperes, volts).
4. Electrons passing through a lamp (gain, lose) some voltage as they light the lamp.
5. Voltage (varies, is the same) in all parts of a series circuit.
6. The current in a circuit is measured in (volts, amperes).
7. Current is almost always the flow of (electrons, protons).
8. When a dry cell is connected in a series, the flow of electrons moves from the (positive,
negative) terminal to the (positive, negative) terminal.
9. The voltage difference between the 2 holes in a wall socket is (12 V, 120V).
10. A car battery is an example of a (dry, wet) cell.
11. Resistance is measured in (ohms, volts).
12. According to Ohm’s law, (I = V/R, V = I/R)
13. The symbol for ohm is (Ω, °).
14. In the equation I = V/R, I is expressed in (ohms, amperes).
15. In the equation I = V/R, V is expressed in (volts, ohms).
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16. A wire with a resistance of 3 Ω has a (greater, lesser) resistance to electron flow than a
wire with a resistance of 5 Ω.
17. If two copper wires are the same length, but different thicknesses, the (thinner, thicker)
wire has greater resistance.
1. Will the voltage in this circuit be greater at A or B? Why?
2. What causes current to flow from one terminal of the battery to the other?
3. If the battery is a 9-volt battery and the resistance in the circuit is 18 ohms, how much
current is flowing through the circuit? Show your work.
4. If a current flowing through a light bulb is 0.75 ampere and the voltage difference across the
light bulb is 120 volts, how much resistance does the light bulb have?
Problem Solving:
Suppose you have purchased a string of lights. You want to find out if the lights are wired in
series or in parallel. How could you quickly determine how the lights have been wired?
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Directions: Underline the term or phrase that correctly completes the sentence.
1. When a current is passed through a coil of wire with a piece of iron inside,
(an electromagnet, a commutator) is formed.
2. An electromagnet is a (permanent, temporary) magnet.
3. Adding more turns to the wire coil (increases, decreases) the strength of an electromagnet.
4. Increasing the amount of current that flows through a wire
(increases, decreases) the strength of an electromagnet.
5. Electromagnets change electrical energy into (chemical, mechanical) energy.
6. An instrument that is used to detect current is (an electromagnet, a galvanometer).
7. An electric motor changes (chemical, electrical) energy into mechanical energy.
9. A coil’s magnetic field can be flipped by (reversing the direction of current,increasing the
number of loops) in the coil.
10. In a motor, a reversing switch that rotates with an electromagnet is called a
commutator).
(voltmeter,
11. In a motor, the stronger the magnetic field in the coil, the (weaker, stronger) the force
between the permanent magnet and the electromagnet.
12. The speed of an electric motor can be controlled by varying the amount of
current, mechanical energy) to the motor.
(electric
13. Name three devices you see or use every day that make use of the relationship between
electricity and magnetism to operate.
1.
2.
3.
14 When the wire loop of a (motor, generator) turns, an electric current is produced.
15. The current produced by a generator is (direct, alternating) current.
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16. A motor (uses, creates) an electric current as it turns.
17. A device that increases or decreases voltage of electric current passing through a
(transformer, motor).
power line is a
1. What serves as the energy source? What kind of energy does it provide?
2. What kind of energy is being produced?
3. What is structure B? What happens to it when energy flows?
4. Does the figure represent an electric motor or a generator? Explain your answer.
5. What happens to the rotation of the coil if the current flowing through it is increased?
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