Grade by Grade
C. Matter and Energy · Electrical Phenomena, Energy, and Devices

Using Electricity: Electrical Energy Into Other Forms

C2.5 A3.3 A1.5About 40 minutes
Learning goals
  • I can describe how devices transform electrical energy into light, heat, sound and motion.
  • I can explain that charging a battery stores electrical energy as chemical energy.
  • I can identify the useful and the wasted energy in an electrical device.
  • I can describe a contribution to electrical technology by an inventor from a community that has often been left out of science stories.

Words to know

transform
To change from one form into another.
useful energy
The energy a device is meant to give, like light from a lamp.
wasted energy
Energy a device gives off that isn't wanted, usually heat. It is not destroyed; it spreads out and can't easily be used.
electric motor
A device that changes electrical energy into motion energy, using magnets and coils of wire.
filament
The thin wire or thread inside an old-style (incandescent) bulb that glows when current flows through it.

One form in, many forms out

Think about the electrical devices you use before school: a light, a toaster, an electric toothbrush, a radio, a phone charger. They all take in the same form of energy: electrical energy. But they give out very different things: light, heat, motion and sound.

The load in a circuit is where this happens. Its job is to transform electrical energy into a form we can use.

A kitchen counter with a toaster glowing inside, a steaming kettle and a lit lamp.
The same electrical energy becomes heat in the toaster and kettle and light in the lamp. Each load transforms it into a different form. AI-generated image
Electricalenergy inLight: LED, screenHeat: toasterSound: speakerMotion: fan, motor
Electrical energy can be transformed into light, heat (thermal energy), sound and motion (kinetic energy).

How devices transform electrical energy

  • Into light: LED bulbs, screens, streetlights and the lights in a hockey arena.
  • Into heat (thermal energy): toasters, kettles, electric stoves, baseboard heaters, hair dryers and clothes irons. Current flowing through special wires makes them hot.
  • Into sound: speakers, headphones, doorbells, buzzers and smoke alarms. Electrical energy makes a part vibrate, and vibrations make sound.
  • Into motion (kinetic energy): anything with an electric motor: fans, blenders, washing machines, electric cars and buses, the subway, power wheelchairs and electric drills. Inside a motor, current flows through coils of wire near magnets, and the push between them makes the motor spin. (A motor works like a generator in reverse!)
  • Into chemical energy: when you charge a phone or a rechargeable battery, electrical energy is stored as chemical energy. Later, the battery changes it back into electrical energy.

Useful and wasted energy

Remember from Grade 5: energy is never destroyed, but some always spreads out (dissipates), usually as heat.

  • A TV: useful energy = light and sound. Wasted = heat (the back gets warm).
  • An old-style (incandescent) bulb: useful = light. Wasted = a lot of heat. Most of the energy it uses becomes heat, not light.
  • An LED bulb: useful = light. Wasted = only a little heat. That's why LEDs use much less electricity for the same amount of light.
  • A toaster: here the heat is the useful energy! The glow (light) is extra.
electricity inenergy outold-style 60 Wlightheat (wasted)LED 9 Wlightheat (wasted)
Energy in and energy out for two bulbs that give about the same light. The old-style bulb takes in 60 W and turns most of it into heat; the LED takes in only 9 W. (Band widths are approximate.)

A bright idea: Lewis Latimer (A3.3)

Early electric light bulbs had a glowing thread inside called a filament, made of carbon. The first ones burned out quickly.

Lewis Latimer was a Black American inventor and draftsman whose parents had escaped from slavery. In 1882, he patented a better way to make the carbon filaments for light bulbs, which helped bulbs last longer and cost less to make. He also helped set up electric lighting systems in cities and wrote one of the early books about electric lighting.

Latimer was largely self-taught. For a long time, contributions by Black inventors like him were left out of many science books. Today we know that people from many communities have shaped the technology we use.

Worked example

Let's analyse a blender

A blender plugs into the wall. Describe the energy transformations, and name the useful and wasted energy.

  1. Energy in: electrical energy from the outlet.
  2. Inside is an electric motor. It changes electrical energy into motion (kinetic) energy that spins the blades.
  3. The blender is loud, so some energy becomes sound.
  4. The motor gets warm, so some becomes heat (thermal energy).
  5. Useful: motion (to blend the smoothie). Wasted: sound and heat.

Electrical → kinetic (useful), plus sound and heat (wasted).

Just for fun

A toaster is the one device that can brag, "My so-called waste heat? That's my whole job!"

Hands-on activity

Electrical energy survey

You need: paper and a pencil.

  1. Make a table with four columns: Device, Energy in, Useful energy out, Wasted energy out.
  2. Find 10 electrical devices in your home, both plug-in and battery-powered. Try to include at least one that makes light, one for heat, one for sound, one for motion, and one that charges a battery.
  3. Fill in your table. Use your senses safely: look and listen while a grown-up runs each device. Ask a grown-up whether a device gets warm instead of touching it.
  4. Circle the device you think wastes the most energy, and explain why.
  5. Share it (A1.5): make a sorting chart: light, heat, sound, motion, chemical. Put each device under its main useful form.

What to look for: correct energy forms (e.g., fan: electrical in → motion useful → sound and heat wasted). Many devices give out more than one form.

Safety: look and listen, don't touch. Never touch plugs, outlets, cords, a hot stove, an iron, a kettle or a heater. Only a grown-up runs kitchen appliances.

Your turn

1

Name a device that transforms electrical energy into light.

2

Name a device that transforms electrical energy into heat.

3

Name a device that transforms electrical energy into sound.

4

What part inside a fan changes electrical energy into motion?

5

When you charge a tablet, what form is the energy stored as?

6

In an LED lamp, what is the useful energy? What is the wasted energy?

7

What did Lewis Latimer invent?

More practice: warm-up

1

Electrical energy into what? A doorbell.

2

Electrical energy into what? A ceiling fan.

3

Electrical energy into what? A toaster.

4

Electrical energy into what? A night light.

5

Electrical energy into what? A phone that is charging.

More practice: on your own

1

Write the energy transformations for a TV. Which energy is wasted?

2

Why does an LED bulb use less electricity than an old-style bulb that gives the same amount of light?

3

For which device is heat the useful energy: a laptop or a kettle? Explain.

4

Write the energy chain for an electric car, from charging to driving.

5

How is a motor like a generator, and how is it different?

Challenge

1

A hair dryer gives off at least three forms of energy. Name them and say which are useful and which are wasted.

2

Why do you think contributions by Black inventors like Lewis Latimer were often left out of older science books? Why does it matter to include them?

3

A device takes in 100 units of electrical energy. It gives out 15 units of light and the rest as heat. How many units of heat? If it is a lamp, is it efficient? Explain.

Check your understanding

Quiz

1.

An electric fan changes electrical energy mainly into...

2.

Which device changes electrical energy mainly into heat?

3.

When you charge a phone, electrical energy is stored as...

4.

In an old-style (incandescent) bulb, most of the energy becomes...

5.

A speaker makes sound by...

6.

Lewis Latimer is known for...

For parents and teachers

Big idea (C2.5): describe how electrical energy is transformed into other forms (light, heat, sound, motion, and chemical energy when charging), and recognize useful versus wasted energy. The Lewis Latimer section supports analysing contributions from various communities (A3.3); the survey chart supports communication (A1.5).

How to help: run kitchen appliances with your child watching and ask: "What's the energy going in? What's coming out? Which part is useful?" Let them observe rather than touch. Older bulbs, if you still have one, are a good comparison with LEDs.

Common difficulties:

  • Naming only one output. Most devices give out more than one form (a blender: motion, sound, heat).
  • Thinking heat is always wasted. For a kettle, toaster or heater, heat is the useful energy.
  • Forgetting that charging stores energy as chemical energy.

Safety: children should not operate kitchen appliances, irons, kettles or heaters on their own, and should never touch plugs or outlets during the survey.