Our Energy Sources, Electricity

♪♪ We’ve talked a lot about

electricity in this unit. We looked at what it is,

the forms it takes, how it behaves, and how we

build circuits to harness it. But where does

the electrical power we use in our everyday

lives come from? Yes, power plants. But there’s more

to it than that.*For instance, take the
McDonough Atkinson Plant,*

of natural gas plant

online in 2012

times as much energy

that it replaced.

do you think we use in the U.S.

every year

more than 412 million megawatt

the month of July.

be somewhere around

hours per year.

user of energy in the world, after China. Any idea where all that

energy comes from? Oil? Dams?

the breakdown is that

is generated from coal,

from natural gas,

from nuclear plants.

produces about 7%,

and solar power about 1%.

for generating electricity

of debate, as you know.

your main energy source

where you live.

power comes from wind.

its power from nuclear plants.

energy is natural gas

like McDonough.

the amount of power that can be

generated is why you can

turn on your lights and power your home

reliably and safely. Let’s look at

how that’s done. Earlier in the series,

output over a span of time

in units of watts.

potential difference, V,

be done on a charge, Q.

difference times charge.

is available to be worked on?

a current in the circuit.

measure of how much charge

point in the circuit

which we can call T.

charge divided by time.

appears in both equations.

link them together?

the current equation,

current multiplied by the time.

this equation

electric potential

to electric potential

multiplied by the time.

both sides by time,

equals voltage

the current.

per unit time?

of what power is

form for electrical power.

voltage times current.

another relationship

Ohm’s law.

write the equation

in a few different ways.

voltage in volts

current in amps,

squared times resistance,

voltage squared

the resistance.

that translates into power that we can see. I’ve got three incandescent

light bulbs here. A dim one, a medium one,

and a bright one. Power is related to the

brightness of the bulb. For bulbs of

the same type, the higher the power rating,

the brighter the bulb. Now, I’m going to unscrew

the dimmest incandescent bulb and replace it with a bulb

that is a different type. An LED, which has one-fifth

the power rating of our brightest bulb. But, before I

turn it on, which incandescent bulb should

this LED bulb be closest to in brightness? Let’s see. It’s the brightest bulb. The one using five times

as much energy as the LED. So, the LED bulb is more than

five times more efficient than the brightest

incandescent bulb, allowing us to use

a fifth as much power to produce equivalent

brightness. In physics,

efficiency is the ratio of the total

energy output divided by the energy

input into a device. We can output power in

the form of light or heat. So, in terms of

lighting brightness, which of these two bulbs

is the most efficient because it loses

less power to heat? Yeah, it’s the LED. Energy efficiency

is important. Because even though energy

cannot be created or destroyed, according to the law of

conservation of energy, the amount we can use and the amount we

lose to wasted heat depends on how

efficient we are. Any idea how efficient

you are as an energy user? You can actually

find out through an online

personal energy audit. You might be really surprised

at what you discover. Before I show you

a quick example, we need to know

how to calculate the amount of

energy we use.

electrical work,

electrical energy,

equals electrical power.

this equation,

energy equals

by the time.

different units

more real to us.

in kilowatt hours,

find on your power bill,

in kilowatts

the time in hours.

much energy we use

as an example.

do I use my microwave?

two hours,

1,100 watts or 1.1 kilowatts.

of the month,

hours of energy.

100 hours a month of TV.

150 watts or .015 kilowatts.

of a month,

hours of energy.

conditioning in my home?

for a typical home

5,000 watts or 5 kilowatts.

of three hours per day,

hours per month.

these three devices together,

of energy used per month.

on average,

hour of energy.

microwave, watch TV,

conditioning each month,

little over $50.

of those three activities, I see ways in which I can save

a lot of energy and money every month. Now, when you go through

your daily routine of turning on lights,

heating your food, and cooling your home, you’ll have a bit

more insight into how it all happens, and how you can affect the

amount of power you use. That’s it for this segment

of “Physics in Motion,” and we’ll see

you next time.

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and note-taking guides,

“Physics in Motion” toolkit.

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