1. Energy Consumption:
HOME

2. Short circuit Overload Circuit breaker Fuse Power
OUTCOME QUESTION(S):
S1-3-18:
How is a household wired to ensure safety?
S1-3-20:
What is electrical power and how does it vary in appliances?
Vocabulary and People
Short circuit Overload
Circuit breaker Fuse Power

3. Common household circuits are 120 volts and 15 amps
House circuits are different than the circuits made with batteries:
Uses alternating current (AC) instead of direct current (DC)
Operates at a higher voltage V or 240 V
Electricity controlled and moved through a main panel (fuse box)
All branches off the main line are in parallel
Common household circuits are 120 volts and 15 amps

4. Generators produce A/C current for the home
DC: electrons travel in one direction – (-) to (+)
AC: e- move back and forth many times a second
DC is like rolling balls down a hill
– need to keep adding more to the top (or run out)
AC is like balls rolling along a teeter totter
– don’t need more since they will just move back and forth
Remember this?
Generators produce A/C current for the home

5. There are 3 wires that bring electricity into a home:
Neutral wire (white)
Two “Hot” wires (black) – carrying 120 V each
Normal use:
1 hot connected to neutral creates 120 V potential
Larger appliances:
Both hot wires connect to neutral creates 240 V
There is also a safety “ground” wire - green or bare copper - removes stray electrons safely

6. Remember what parallel circuits offer…
All house branch lines link from the main panel.
Outlets and switches are all connected in parallel
each branch delivers typical 120 volts
total current of all branches equals 15 A
break any branch without affecting any other
Remember what parallel circuits offer…

7. There are two components that safeguard against an increase in current
Safety issues:
Short circuit: current bypasses the appliance.
less resistance – increases branch current
Branch heats up – risk of fire
Overload: too many things plugged into one outlet.
increased branching – increases total current
Main heats up – risk of fire
There are two components that safeguard against an increase in current A

8. Fuses “burn out” and need to be replaced
Circuit Breaker:
contain either magnet / metal / semiconductor
all are altered by excess current - breaks circuit (kill switch)
Fuse:
uses a strip of metal that easily melts
excess current heats metal – breaks circuit
main
Breakers can be reset
Fuses “burn out” and need to be replaced A
main

9. Power and Energy Consumption
Power is a measure of energy used over time:
lifting heavier weight in the same time – more power
heating a cold room faster – more power P = t E
E is energy in joules
t is the time in seconds
Power – measured in watts – is the energy
used or work done every second
1 Watt is the power of 1 joule of energy in 1 second

10. What is the power of the charger?
An iPhone charger moves joules of energy in the 4 hours to fully charge a drained battery.
What is the power of the charger? P = t E
Formula must be in seconds to work properly
– time must be converted
4 h · 60 min · 60 sec =
1 h 1 min
sec P =
14400 seconds
72000 joules
= 5 watts (W)

11. Formula must be rearranged here to solve for the new unknown
How much energy, in joules, is consumed by a
120 W light bulb if it is left on for 15 min? P = t E E
Formula must be rearranged here to solve for the new unknown t P = t t
P · t = E
15 min · 60 sec =
1 min
900 sec E =
120 W · 900 sec
= J

12. Rarely do we know energy values, but we can find voltage and current requirements - sometimes they are written on the component. P = t E P =
V · I E Q P =
V · I Q t
Remember:
Voltage = ENERGY per coulomb of electrons
Current = coulombs of electrons per SECOND

13. A 10 amp car heater is plugged in to a standard house outlet
A 10 amp car heater is plugged in to a standard house outlet. What is the power of the heater? P =
V · I
Standard home outlet is 120V P =
120 V · 10 A P =
1200 W
Large power measurements are converted to kilowatts
1200 W · 1 kW =
1000 W
1.2 kW

14. Formula must be rearranged here to solve for the new unknown
What is the current through a 1200 W hair dryer if it is connected to 120 V?
Formula must be rearranged here to solve for the new unknown P =
V · I P =
V · I V V P V = I I =
1200 W
120 V
= 10 A

15. CAN YOU ANSWER THESE QUESTIONS? S1-3-18: S1-3-20:
How is a household wired to ensure safety?
S1-3-20:
What is electrical power and how does it vary in appliances?
Vocabulary and People
Short circuit Overload
Circuit breaker Fuse Power