1. Ch. 7 - Electricity
SPS10.
Students will investigate the properties of electricity and magnetism.
a. Investigate static electricity in terms of friction, induction, conduction
b. Explain the flow of electrons in terms of alternating and direct current. the relationship among voltage, resistance and current. simple series and parallel circuits. 1 1

2. Ch. 7 - Electricity I. Electric Charge Static Electricity Conductors
Insulators
Electroscope 1 1

3. A. Static Electricity Static Electricity
the net accumulation of electric charges on an object
Electric Field
force exerted by an e- on anything that has an electric charge
opposite charges attract
like charges repel

4. A. Static Electricity Static Discharge
the movement of electrons to relieve a separation in charge

5. A. Static Electricity Three ways to achieve static electricity
Friction
Rubbing together two objects
Induction
Inducing a positive or negative charge
Conduction
Transferring a positive or negative charge
Demo on Static Electricity

6. B. Conductors Conductor
material that allows electrons to move through it easily
e- are loosely held
ex: metals like copper and silver

7. C. Insulators Insulator
material that doesn’t allow electrons to move through it easily
e- are tightly held
ex: plastic, wood, rubber, glass

8. D. Electroscope Electroscope
instrument that detects the presence of electrical charges
leaves separate when they gain either a + or - charge

9. Ch. 7 - Electricity II. Electric Current Circuit Potential Difference
Resistance
Ohm’s Law

10. A. Circuit
Circuit
closed path through which electrons can flow

11. A. Potential Difference
Potential Difference (voltage)
difference in electrical potential between two places
large separation of charge creates high voltage
the “push” that causes e- to move from - to +
measured in volts (V)

12. B. Current Current flow of electrons through a conductor
depends on # of e- passing a point in a given time
measured in amperes (A)

13. C. Resistance Resistance opposition the flow of electrons
electrical energy is converted to thermal energy & light
measured in ohms ()
Tungsten - high resistance
Copper - low resistance

14. C. Resistance Resistance depends on… the conductor wire thickness
less resistance in thicker wires
wire length
less resistance in shorter wires
temp - less resistance at low temps

15. V = I × R E. Ohm’s Law V: potential difference (V) I: current (A)
R: resistance ()
V = I × R
Voltage increases when current increases.
Voltage decreases when resistance increases.

16. E. Ohm’s Law R = 160  V= I * R V = 120 V I = V ÷ R I = ?
A light bulb with a resistance of 160  is plugged into a 120-V outlet. What is the current flowing through the bulb?
GIVEN:
R = 160 
V = 120 V
I = ?
WORK:
V= I * R
Divide both sides by R
I = V ÷ R
I = (120 V) ÷ (160 )
I = 0.75 A

17. E. Ohm’s Law R = 50  V= I * R V = 110 V I = V ÷ R I = ?
A cell phone with a resistance of 50  is plugged into a 110-V outlet. What is the current flowing through the bulb?
GIVEN:
R = 50 
V = 110 V
I = ?
WORK:
V= I * R
Divide both sides by R
I = V ÷ R
I = (110 V) ÷ (50 )
I = 2.2 A

18. E. Ohm’s Law R = ?  V= I * R V = 120 V R = V ÷ I I = 4.25
A Television is plugged into a 120-V outlet. How much resistance does it have if the current is measured to be 4.25 A?
GIVEN:
R = ? 
V = 120 V
I = 4.25
WORK:
V= I * R
Divide both sides by R
R = V ÷ I
R = (120 V) ÷ (4.25 A)
R = 28.2 

19. III. Electrical Circuits
Ch. 7 - Electricity
III. Electrical Circuits
Circuit components
Series circuits
Parallel circuits
Household circuits

20. A. Circuit Components A - battery C - light bulb
B - switch D - resistor

21. B. Series Circuits Series Circuit current travels in a single path
one break stops the flow of current
current is the same throughout circuit
lights are equal brightness
each device receives a fraction of the total voltage
get dimmer as lights are added

22. C. Parallel Circuits Parallel Circuits
current travels in multiple paths
one break doesn’t stop flow
current varies in different branches
takes path of least resistance
“bigger” light would be dimmer
each device receives the total voltage
no change when lights are added

23. D. Household Circuits Combination of parallel circuits
too many devices can cause wires to overheat
Safety Features:
fuse - metal melts, breaking circuit
circuit breaker - bimetallic strip bends when hot, breaking circuit

24. IV. Measuring Electricity Electrical Power Electrical Energy
Ch. 7 - Electricity
IV. Measuring Electricity
Electrical Power
Electrical Energy

25. P = I × V A. Electrical Power P: power (W) I: current (A) V: potential
rate at which electrical energy is converted to another form of energy
P: power (W)
I: current (A)
V: potential
difference (V)
P = I × V

26. A. Electrical Power I = 0.01 A P = I · V V = 9 V P = (0.01 A) (9 V)
A calculator has a 0.01-A current flowing through it. It operates with a potential difference of 9 V. How much power does it use?
GIVEN:
I = 0.01 A
V = 9 V
P = ?
WORK:
P = I · V
P = (0.01 A) (9 V)
P = 0.09 W

27. A. Electrical Power I = 0.05 A P = I · V V = 8 V P = (0.05 A) (8 V)
A flashlight has a 0.05-A current flowing through it. It operates with a potential difference of 8 V. How much power does it use?
GIVEN:
I = 0.05 A
V = 8 V
P = ?
WORK:
P = I · V
P = (0.05 A) (8 V)
P = 0.4 W

28. E = P × t B. Electrical Energy E: energy (kWh) P: power (kW)
energy use of an appliance depends on power required and time used
E: energy (kWh)
P: power (kW)
t: time (h)
E = P × t

29. B. Electrical Energy P = 700 W E = P · t = 0.7 kW E = (0.7 kW) (10 h)
A refrigerator is a major user of electrical power. If it uses 700 W and runs 10 hours each day, how much energy (in kWh) is used in one day?
GIVEN:
P = 700 W
= 0.7 kW
t = 10 h
E = ?
WORK:
E = P · t
E = (0.7 kW) (10 h)
E = 7 kWh

30. B. Electrical Energy P = 900 W E = P · t = 0.9 kW E = (0.9 kW) (14 h)
A refrigerator is a major user of electrical power. If it uses 700 W and runs 10 hours each day, how much energy (in kWh) is used in one day?
GIVEN:
P = 900 W
= 0.9 kW
t = 14 h
E = ?
WORK:
E = P · t
E = (0.9 kW) (14 h)
E = 12.6 kWh