# Electric and Magnetic Phenomena

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Electric and Magnetic Phenomena
5. Electric and magnetic phenomena are related and have many practical applications. As a basis for understanding this concept: Standard 5 Electricity

1. Static electricity is a part of life
1. Static electricity is a part of life. Can you name at least five examples of static electricity that occur in your home? 2. Fabric softeners are commonly used today because they eliminate static cling. Explain why clothes in the dryer get static cling. Electricity

3. Why can walking across a carpeted room be a shocking experience?
4. Magnets have both north and south poles. While like poles repel each other, opposite poles attract each other. Explain the parallelism between magnetism and electric charge. Electricity

Electric Charge and Force
Electricity Electric Charge and Force Electricity Electricity

Electric Charge Electrical property of matter
Creates a force between objects Positive or Negative Electricity

Electric Charge Opposite charges Attract Like charges Repel
Electricity

3. The electric force between charged objects is c. either attractive or repulsive. Electricity

Electrical Charge Depends on the imbalance of electrons and protons
Protons = positive Electrons = negative Neutron = neutral Leads to a net charge Electricity

2. When there is an equal amount of positive and negative charges on an object, the object is
c. neutral. Electricity

Coulomb SI unit for charge Proton = +1.6 x 10-19 C
Electron = -1.6 x 10-19C Charges are equal and opposite Electricity

Flow of Charge Conductor Insulator
Material that transfers charge easily Insulator Material that does not transfers charge easily Electricity

Charging by Contact Electrons move from the rod to the doorknob
Skill Builder: Interpreting Visuals, ATE p Have students explain what would happen if a positively charged rod were touched to the doorknob. Teaching Transparency TT 38 Charging by Contract is available as a visual aid. Electrons move from the rod to the doorknob Electricity Electricity

Charging by Contact Transfer of electrons
Gives the doorknob a negative charge Electricity

Induced Charges Induces a positive charge near the rod
Induces a negative charge away from the rod Skill Builder: Interpreting Visuals, ATE p Have students explain what will happen to the doorknob when the negatively charged rod is removed. Teaching Transparency TT 39 Induced Charges is available as a visual aid. Electricity Electricity

Induced Charges Electricity
Discuss the polarization of the molecules in the tissue paper. Electricity Electricity

i. Students know plasmas, the fourth state of matter, contain ions or free electrons or both and conduct electricity. Electricity

Charging by Friction When rubbed together electrons can be transferred from one material to the other material that gets the electrons becomes negatively charged material that loses the electrons becomes positively charged Electricity

Electric Force The force of attraction or repulsion between objects
Due to charge Without electric force life would be impossible Depends on charge and distance Attraction and repulsion are examples of Electric Force. Electricity Electricity

Electric Force Proportional to the product of the charges
Inversely proportional to the distance between them squared Equation: F = q1 q2 /[4peo r2 ] Electricity

e. Students know charged particles are sources of electric fields and are subject to the forces of the electric fields from other charges. Electricity

Electric Field Produced around charged particles
Other charged objects around will experience an electric force Electric force acts through electric fields Electricity

4. Every charged particle produces d. an electric field.
Electricity

Point Charges Electric field lines point in the direction of the electric force on a positive charge Electricity

Point Charges Positive is attracted to negative
Electric Field lines point inward Electricity

Electric Field Lines Show direction of electric force
Also show relative strength Electricity

Electric Fields Electricity

Electric Fields In the figure shown, why do only half of the lines originating from the positive charge terminate on the negative charge? When compared to a 2 charge, there are c. twice as many field lines pointing outward from a 4 charge. Because the positive charge is twice as great as the negative charge. Electricity Electricity

Electric Force varies depending on
charge and distance between charged objects Electricity

Students know how to predict the voltage or current in simple direct current (DC) electric circuits constructed from batteries, wires, resistors, and capacitors. Electricity

b. Students know how to solve problems involving Ohm’s law.
Electricity

c. Students know any resistive element in a DC circuit dissipates energy, which heats the resistor. Students can calculate the power (rate of energy dissipation) in any resistive circuit element by using the formula Power = IR (potential difference) x I (current) = I 2 R. Electricity

d. Students know the properties of transistors and the role of transistors in electric circuits. Electricity

Electrical Potential Energy
Potential energy of charged object Due to its position in electric field Electricity

16. What determines the electrical potential energy of a charge
Determined by the position of the charge relative to all the other electrical charges Electricity

Electrical Potential Energy
Shows how the epe depends on the distance between the two charged particles. Electricity Electricity

Electricity

Potential Difference Change in the electrical potential energy per unit charge Measured in Joule / Coulomb 1 J/C = 1 volt or 1V or voltage Electricity

Volts Measure of potential difference
Terminals of a battery have a potential difference Cell (battery) Source of current Voltage across the terminals Electricity

Dry Cell and Car Battery
Electricity

Batteries Typically have one positive and one negative terminal.
Electricity

Current Voltage sets charges in motion
Current = Rate of electric charges moving through a conductor 1 C/s = 1 ampere or 1 amp Electricity

Electric Current Produced when charges are accelerated by an electric field Charges move to a position of potential energy that is lower Electricity

7. Current is the rate at which charges move through a(n) a. conductor. b. insulator.   Electricity

Electrical Resistance
What is the voltage from the wall? 120 V What is the power of a bulb? 40W, 60W, 100W Electricity

5. Resistance is caused by internal friction. 6
5. Resistance is caused by internal friction. 6. The SI unit of resistance is the c. ohm. Electricity

Electrical Resistance
Causes changes in current Caused by internal friction Slows the movement of charges through collisions Collisions can cause material to heat up Electricity

Electrical Resistance (Ohm’s Law)
Resistance = voltage/current R = V / I  = V / A  = Ohm Electricity

Resistance A set of electric trains is powered by a 9 V battery. What is the resistance of the trains if they draw 3.0 A of current? Answer: 3  Electricity

Resistance A battery-operated CD player uses 12 V from the wall socket and draws a current of 2.5 A. Calculate the resistance of the CD player. Electricity

Resistance There is a potential difference of 12 V across a resistor with 0.25 A of current in it. The resistance of the resistor is Answer: 48 Electricity

Ohms Law A light bulb has a resistance of 12 . It is attached to a battery that has a voltage of 24 V. Calculate the current in the light bulb. Answer: 2 A Electricity

Current A resistor has a resistance of 280. How much current is in the resistor if there is a potential difference of 120 V across the resistor? Answer: 0.43 A Electricity

17. A resistor has a resistance of 1.8-ohm. How much current is in the resistor if there is a potential difference of 3.0 V across the resistor? Answer: 1.67 A   Electricity

9. A 13-ohm resistor has A of current in it. What is the potential difference across the resistor? Answer: V   Electricity

Electricity

Series Circuits Electricity

Series Circuits Electricity

Parallel Circuits Electricity

Parallel Circuits Electricity

18. Which bulb(s) will have a current in the schematic diagram above?
Only the first light bulb will light. The other two bulbs are beyond the open switch and therefore, will not receive current. Electricity

19. Does the schematic diagram above represent a series or parallel circuit? Answer: series circuit Electricity

19. Does the schematic diagram above represent a series or parallel circuit? Electricity

18. Is a current flowing in the schematic diagram above? Explain your answer. Electricity

10. What happens to the resistance of a superconductor when its temperature drops below the critical temperature? Answer: Resistance drops to zero. Electricity

Electric Energy Energy associated with electrical charges
Whether moving or at rest Electricity

Electrical Power Rate at which electrical energy is used in a circuit
power = current x voltage P = IV 1 Watt = 1 Amp x 1 Volt Electricity

A color television draws about 2
A color television draws about 2.5 A when it is connected to a 120 V outlet. Assuming electrical energy costs \$0.060 per kWh, what is the cost of running the television for exactly 8 hours? Answer: \$0.14 Electricity

8. A flashlight bulb with a potential difference of 4.5 V across its filament has a power output of 8.0 W. How much current is in the bulb filament? Answer: 1.8 A   Electricity

Household Circuits Electricity

7. What is the potential difference across a resistor that dissipates 5.00 W of power and has a current of 5.0 A? Answer: 1.00 V Electricity

11. If a lamp is measured to have a resistance of 120- when it operates at a power of 120 W, what is the potential difference across the lamp? Answer: 120 V Electricity

12. A microwave draws 5.0 A when it is connected to a 120 V outlet. If electrical energy cost \$0.090/kWh, what is the cost of running the microwave for exactly 6 hours? Answer: \$0.32 Electricity

13. What happens to the overall resistance of a circuit when too many appliances are connected across a 120 V outlet? Answer: Resistance is decreased. Electricity

11. An electric toaster has a power rating of 1100 W at 110 V. What is the resistance of the heating coil? Answer: 11   Electricity

13. A device that protects a circuit from current overload is called a(n) Answer: circuit breaker. Electricity

14. What is charging by contact? Electricity

16. A 180-ohm resistor has 0.10 A of current in it. What is the potential difference across the resistor? Answer: 18 V Electricity

Study Guide Attraction, repulsion Electric force Batteries
Current, potential Resistance Ohm’s law: V=IR Power, P = VI Circuits, parallel, series Charge/ing, Electric fields Conductor, insulator Electricity