learning goals

Electrical energy can be transformed into other forms.
Electrical energy heats the filament in an incandescent light bulb. The filament becomes so hot that it glows and emits light.
Heat in a filament is produced by the resistance to the flow of charges.

Discovery question

What kinds of energy does a bulb produce?
Measure the temperature of a holiday light.

Engage

One wonderful thing about electrical energy is that it can be transformed into other forms of energy that are are useful for many purposes. However, this transformation is never 100% efficient. That is, the total amount of energy stays the same, but some of it becomes heat.

Make a list of electrical devices that produce mainly heat.
ANSWER BOX

Make a list of electrical devices that produce mainly light.
ANSWER BOX

Suppose you could measure all of the light and heat energy coming out of a regular incandescent bulb.

What do you think the energy would be?

• mainly light
• mainly heat
• about the same amount of light and heat.
  (answer: mainly heat. Less than 10% of the energy is emitted as light.)

If you compared the light and heat energy coming out with the electrical energy coming in,

• they would be the same
• the energy coming out would be greater
• the energy coming out would be less
  (answer: the same)
  Why do you think so?
  ANSWER BOX

(answer: the total energy is the same, even though it changes form.)

Materials

Temperature sensor, fast response
Holiday light
Battery (AA 1.5V)
Clear tape
Aluminum foil (small piece)
Rubber band
Paper clamp
Extra wire (The leads on the holiday light may not be long enough to connect to two batteries.)

Explore

It's hard to measure the total amount of heat energy coming a light bulb, but measuring the temperature will give you some sense of how much heat is being produced. You can observe how fast the bulb heats up.

The fast response temperature sensor has a tiny tip that measures temperature. Put the tip against the holiday light and hold it in place with a small piece of clear tape.
Cannot resolve external resource into attachment.

Get ready to connect the two leads of the light to the two ends of the battery, but don't do it yet.

Attach the temperature sensor to the computer. Choose the "clear" dataset. Start recording temperature. Let it run for ten seconds.

TEMPERATURE SENSOR - multiple dataset with two created datasets: "clear" and "foil".

After exactly ten seconds, hold the two leads from the holiday light against the two ends of the battery.

Cannot resolve external resource into attachment.
Watch the temperature plot. Let it run for 30 seconds, then disconnect leads from the battery and let it run for another 30 seconds. Stop recording the data.

Expand the graph so that you can see how much the temperature rose while the battery was attached and how much it decreased after you stopped.
NEED TECHNICAL HINT ABOUT EXPLAINING GRAPH

How many degrees did the bulb heat up in 30 seconds?
ANSWER BOX

How many degrees did the bulb cool down in 30 seconds?
ANSWER BOX

Repeat your experiment, but this time wrap the holiday light with aluminum foil. Remove the tape from your first experiment. Wrap a small piece of foil around the entire bulb. Hold the foil in place with a short piece of clear tape.

Slide the tip of the Temperature probe in between the bulb and the aluminum foil.

Cannot resolve external resource into attachment.

Get ready to connect the two leads of the light to the two ends of the battery, but don't do it yet.

Attach the temperature sensor to the computer. Choose the "foil" dataset. Start recording temperature. Let it run for ten seconds.

TEMPERATURE SENSOR - multiple dataset – same as the previous one.

After exactly ten seconds, hold the two leads from the holiday light against the two ends of the battery.

Watch the temperature plot. Let it run for 30 seconds, then disconnect leads from the battery and let it run for another 30 seconds. Stop recording the data.

Expand the graph so that you can see how much the temperature rose while the battery was attached and how much it decreased after you stopped.

How many degrees did the bulb heat up in 30 seconds?
ANSWER BOX

How many degrees did the bulb cool down in 30 seconds?
ANSWER BOX

Compare the measurement with tape and the measurement with foil. Which one produced more heating of the bulb?
ANSWER BOX
(scaffolding: note how much the temperature changed in the 30 seconds that the battery was connected. )

Explain

Compare the measurement with tape and the measurement with foil. Which one produced more heating of the bulb?
ANSWER BOX
(scaffolding: note how much the temperature changed in the 30 seconds that the battery was connected. )
(answer: Probably the foil will show more heating, because the light energy is directed back into the bulb by the foil.)

Does the temperature change show that some of the electrical energy is turned into heat?

• yes
• no

One theory is that the clear tape allows light energy to escape from the bulb, and the foil reflects the light energy back into the bulb. Do your observations support this theory?

• yes
• no

Explain why.
ANSWER BOX
(answer: If the foil shows more heating, that would support this theory.)

add idea of resistance.
dont use word current.

Here is how an incandescent light works. The tiny wire inside the glass (called a filament) resists the flow of charges through the circuit. This resistance heats up the wire until it glows. If it is very hot, about 2500 C (4500 F), it glows "white-hot" and gives off white light. If there is less flow of electric charge, the filament is cooler and glows "red-hot".

In this experiment, what was the color of your filament?

• red
• orange
• white

Elaborate

Which one cooled off more when the battery was disconnected?
ANSWER BOX
(scaffolding: note how much the temperature changed in the 30 seconds after the battery was disconnected.)

Why do you think clear tape would be different from foil?
ANSWER BOX
(scaffolding: the foil reflects the light energy back into the bulb, contributing to the heating. The clear tape lets the light energy escape.)

Evaluate

In this experiment, you measured temperature as an indicator of heat energy. You didn't measure light energy. However, based on this experiment, what do you think now about the amount of heat and light energy? The energy produced by the bulb is:

• mainly light
• mainly heat
• about the same amount of light and heat.
  (answer: mainly heat)

Why do you think so?
ANSWER BOX
(scaffolding: It's mainly heat. The light a a bi-product of heating the filament. But there may be a range of observations here.)

Fluorescent bulbs don't get very hot, compared to incandescent bulbs. Do you think that mean that they are more efficient?

• yes
• no
• the same

Why do you think so?
ANSWER BOX
(answer: Since most of the wasted energy in an incandescent bulb is heat, it seems likely that a fluorescent bulb is more efficient. )