Warm-up Activity• Think about your experience with the PhET

circuit simulation that you recently completed

• Record in your notebook:– Two things that you enjoyed/learned from the

lab– One thing that you feel you didn’t understand

• Discuss your responses with your group members

Electrical Power & Energy

Electrical Energy

• Most electrical energy is produced from natural resources and provided to our homes by Electrical Utility Companies.

How does the electrical company produce energy?

Circuits(energy transformation tools)

• Circuits are a way to convert electrical energy into energy we need such as heat and light.

Electrical Power

The rate at which the electrical energy is converted into useful energy such as heat or light (depends

on the device).

60 Watts 100 WattsThis light bulb takes 60 Joules of energy from the circuit every second!

This light bulb takes 100 Joules of energy from the circuit every second!

Electrical Power

P = IVPower (Watts)

Current (Amps) Voltage (Volts)

Example

A lamp operates with a current of .83 A and a potential difference of 120 V. How much power does the lamp use?

Electrical Energy

• Amount of energy used depends upon power requirements by appliances and how long they are used

E = PtEnergy (kWh)

(J)Power (kW)

(W)

Time (hrs)

(s)

Household Circuits

• Standard voltage in U.S. 120V

• Main switch and circuit breaker box serve as “electrical headquarters” for your home

• Many appliances can draw current from the same circuit. A fuse or circuit breaker is wired in between each parallel circuit.

Electrical Energy Problem

A 60 W lightbulb is left on for 8.5 hours. How many kWh of energy are used? How many Joules of energy are used?

Assume Xcel energy charges $.10 per kWh (or per 3,600,000 Joules). How much would it cost to run the lightbulb in the previous question for one week (assuming it was on 8.5 hrs/day)

Electrical Safety

• Correct wiring, fuses, circuit breakers, insulation and grounded plugs help make electrical energy safe

Energy in your home

• Draw on your personal experiences to calculate your family’s energy usage!

• Think of a normal week when all members of your family are home

• Determine how many hours each appliance is actually used

• If there is more than one of the same type of appliance in your house, count all of them toward your total!

A scent plug in uses 120 V of potential difference and a current of 1.1. A to

operate. How much power is the scent plug-in using?

1 2 3 4

25% 25%25%25%

1. 109.1 W

2. 132 W

3. 121.1 W

4. Not enough information

If the scent plug in has a power rating of 132 W, what is the power in kW?

1 2 3 4

25% 25%25%25%

1. 132000 kW

2. 13.2 kW

3. 0.132 kW

4. 0.000132 kW

If the scent plug in uses 0.132 kW of power and is plugged in at all times, how many

kilowatt-hours of Energy are used in 1 week?

1 2 3 4

25% 25%25%25%

1. 22.18 kWh

2. 3.168 kWh

3. 1272.7 kWh

4. Less than 1 kWh

If the energy company charges $0.10 for every kWh of energy used, how much would

you be chared for 22.18 kWh of usage?

1 2 3 4

25% 25%25%25%

1. $0.79

2. $1.50

3. $221.80

4. $2.22

Are the Vikings going to beat the Packers tomorrow?

1 2 3 4 5 6

17% 17% 17%17%17%17%1. Definitely

2. Yes

3. Most Definitely

4. No

5. Guaranteed

6. Yes