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Thermal images of people and objects

Thermal images of people and objects (Kristopher_K, iStockphoto)

STEM in Context

Thermopower and the Body Heat-Powered Flashlight

Eric Mills & Let's Talk Science

Summary

Can your body be a source of electricity generation? Maybe, if you understand heat transfer. Explore this concept through a 2013 invention by a Canadian teen.

Imagine this. You’re at home. There’s a blackout. You can’t see a thing. You try every flashlight in the house. But all of them have dead batteries! Wouldn't it be great if you had a flashlight that could generate electricity from the heat of your hand? 

Sound impossible? It isn’t! In 2013, a Canadian scientist named Ann Makosinski invented a flashlight that could do exactly this. She was 15 years old at the time! 

Body heat is a convenient energy source. So why don’t we power everything that way? After all, heat is one of the most abundant forms of energy. Unfortunately, it’s also a form of energy that’s very hard to put to work.

What is heat energy?

Heat is a form of energy that is associated with the motion of atoms, molecules and other particles. Everything above absolute zero (-273 degrees Celsius) has some heat energy. That is pretty much everything around you! As temperature increases, the molecules move faster and faster. This results in heat energy.

Heat is measured in joules (J) or sometimes in calories (cal). A calorie is the amount of energy required to raise the temperature of 1 gram of water by 1 degree Celsius. The energy in the food you eat is measured in calories.

Do humans give off heat energy?

Humans radiate (give off) about 350 000 joules of heat energy every hour. This energy is a waste product of our body using the food we eat. 1 W (watt) is equal to 1 J/s. That means you give off close to enough heat energy to power a 100 W light bulb all of the time! 

Thermal image of a hand
Thermal image of a hand (Source: Jarek Tuszyński [CC BY-SA 3.0] via Wikimedia Commons).

Normally, we do not do much with the heat energy we give off. It just radiates out into our environment. But imagine if we could capture that heat energy and use it in some way. This is what Ann Makosinski did when she designed and built a body heat-powered flashlight. 

How is heat transferred?

In short, heat is a way for energy to be exchanged between a system and its surroundings. Heat can be transferred in three ways:

Heat transfer methods include conduction, convection and radiation
Boiling water in a kettle on the stove is a good example of the heat transfer processes of conduction, convection and radiation (Let’s Talk Science based on an image from inkoly via iStockphoto).

What is conduction?

One way that heat can be transferred is through conduction. Conduction involves the transfer of heat (heat flow) within and between materials and objects that are in direct contact with each other. 

When a warmer object comes into contact with a cooler one, the cooler object will get warmer. Eventually, the temperatures between the two objects will become equal. The flow of heat energy is always in the direction from a warmer body to the cooler body.

How does this happen? When molecules get warmer, they vibrate (move back and forth) faster. This means that molecules at the warmer end of an object will vibrate faster than molecules at the colder end of an object. The faster molecules will collide with the slower molecules. This makes the slower molecules vibrate faster and get warmer.

Have you ever seen a blacksmith at work? If so, you may have seen them heat a metal rod in a fire. Thanks to conduction, energy from the hot end of that rod will transfer to the colder end. This will continue until the temperature of the entire rod is the same. That’s why it is important for blacksmiths to wear gloves when they’re handling rods!   

Blacksmith hammering a red hot piece of metal
Blacksmith hammering a red-hot piece of metal (Source: Sabine Schulte via Pixabay).

Did you know?

Wooden spoons are a favourite of chefs because they are not good conductors of heat energy. This means the spoons won't heat up too quickly and burn their hands. 

What is thermopower?

Thermopower is an object’s ability to generate electricity from heat flow. Electric current flows when electrons move in one direction through a conductor. Most metals make good conductors. When a conductor heats up, its electrons begin to move quicker and spread out. They bump into the slower moving electrons in the cold part of the conductor. This causes these electrons to heat up and move more quickly. So, if one end of a conductor is heated, the electrons will eventually transfer their energy through the entire conductor, from the hot end to the cool end. This produces an electric current. 

Did you know?

The thermopower effect was discovered in 1821. However, electrons weren't discovered until 1897, and the effect wasn't fully understood until the mid 20th century.

How did Ann Makosinski make a body-powered flashlight?

Can I power a flashlight without batteries? | Ann Makosinski (2014) by Google Science Fair (2:17 min.).

A cleverly-designed circuit will keep the electrons moving for as long as there is heat flow. For her flashlight, Makosinski used a device called a Peltier tile to convert heat flow into electricity. A Peltier tile uses the Peltier effect.

A Peltier tile is made up of two ceramic tiles placed on top of each other. In between, the tiles small pieces of conductor are arranged. Think of a sandwich. The ceramic tiles are like the two pieces of bread. The conductor is like the meat in the middle. When one side of the Peltier tile is heated and the other is cooled, an electric current is generated.

Did you know?

Most water coolers contain Peltier tiles.  

Parts of a Peltier Tile
Parts of a Peltier tile including ceramic tiles, conductors and electrical connections (© 2019 Let’s Talk Science).

Makosinski also used a transformer to increase the voltage. She also used very efficient LED lights to make the most of what little electricity she could generate with the Peltier tiles.

Can you use your body heat to power your devices?

The amount of electricity you can produce by harnessing the flow of heat from your body to the air around you may not be very large. But it could be enough to charge cell phones and various types of wearable devices. Who wouldn’t want to live in a future where you never have to plug in your phone?

The problem with inventions | Ann Makosinski | TEDxVictoria (2014) by TEDx Talks (9:18 min.).

Did you know?

Makosinski’s latest invention is called the eDrink. It’s a mug that stores excess heat energy from your hot beverage. Later, you can use that heat energy to charge your cell phone! 
 

Starting Points

Connecting and Relating
  • Have you ever experienced the feeling that your body was giving off a lot of heat? When did you feel this way? 
  • Would you purchase a flashlight powered by body heat? What factors would aid in your decision?
     
Connecting and Relating
  • Have you ever experienced the feeling that your body was giving off a lot of heat? When did you feel this way? 
  • Would you purchase a flashlight powered by body heat? What factors would aid in your decision?
     
Relating Science and Technology to Society and the Environment
  • What impact might a body heat-powered device have on the environment with respect to consumption and waste?
  • What are some other technologies that make use of Peltier tiles? (Note: this question may require additional research.)
     
Relating Science and Technology to Society and the Environment
  • What impact might a body heat-powered device have on the environment with respect to consumption and waste?
  • What are some other technologies that make use of Peltier tiles? (Note: this question may require additional research.)
     
Exploring Concepts
  • How does the body heat-powered flashlight operate? 
  • What ways can heat be transferred? Define each way. (Note: this question may require additional research.)
  • How does the body heat-powered flashlight differ from a mechanically-powered flashlight? Which aspects of its design are similar and which aspects are different? 
     
Exploring Concepts
  • How does the body heat-powered flashlight operate? 
  • What ways can heat be transferred? Define each way. (Note: this question may require additional research.)
  • How does the body heat-powered flashlight differ from a mechanically-powered flashlight? Which aspects of its design are similar and which aspects are different? 
     
Nature of Science/Nature of Technology
  • The development of a body heat-powered flashlight is a great example of how science and technology are intertwined. Making reference to the article, explain the science-technology relationship. 
  • If you were to design a body-heat powered device, what would it be?
     
Nature of Science/Nature of Technology
  • The development of a body heat-powered flashlight is a great example of how science and technology are intertwined. Making reference to the article, explain the science-technology relationship. 
  • If you were to design a body-heat powered device, what would it be?
     
Media Literacy
  • How are technologies such as the body heat-powered flashlight discussed in the media?
  • Does the media overinflate the potential or current capabilities of new technologies? Explain using examples.
     
Media Literacy
  • How are technologies such as the body heat-powered flashlight discussed in the media?
  • Does the media overinflate the potential or current capabilities of new technologies? Explain using examples.
     
Teaching Suggestions
  • This article can be used in Chemistry, Engineering & Technology, Math & Physics, and Nature of Science to support teaching and learning related to electricity generation, electrical technologies and heat transfer. Concepts introduced include heat, energy, energy source, absolute zero, heat transfer, conduction, thermopower, conductor, electric current and Peltier tile.
  • After reading the article, teachers could have students consider the pros and cons of replacing battery operated flashlights with body heat-powered flashlights. Download ready-to-use reproducibles using the Pros & Cons Organizer learning strategy for this article in [Google doc] and [PDF] formats.
  • Students could also consider the cost-benefit of replacing traditional, battery-operated technology with body heat-powered technology. Download ready-to-use reproducibles using the Cost-Benefit Analysis learning strategy for this article in [Google doc] and [PDF] formats.
  • To consolidate learning, teachers could provide students with an Exit Slip to complete. Download ready-to-use reproducibles using the Exit Slip learning strategy for this article in [Google doc] and [PDF] formats.
Teaching Suggestions
  • This article can be used in Chemistry, Engineering & Technology, Math & Physics, and Nature of Science to support teaching and learning related to electricity generation, electrical technologies and heat transfer. Concepts introduced include heat, energy, energy source, absolute zero, heat transfer, conduction, thermopower, conductor, electric current and Peltier tile.
  • After reading the article, teachers could have students consider the pros and cons of replacing battery operated flashlights with body heat-powered flashlights. Download ready-to-use reproducibles using the Pros & Cons Organizer learning strategy for this article in [Google doc] and [PDF] formats.
  • Students could also consider the cost-benefit of replacing traditional, battery-operated technology with body heat-powered technology. Download ready-to-use reproducibles using the Cost-Benefit Analysis learning strategy for this article in [Google doc] and [PDF] formats.
  • To consolidate learning, teachers could provide students with an Exit Slip to complete. Download ready-to-use reproducibles using the Exit Slip learning strategy for this article in [Google doc] and [PDF] formats.

Learn more

Conductors and Insulators

This article on HyperPhysics looks at conductors, insulators, circuits, and how they work.

Harnessing Body Heat to Power Electronic Devices (2018)

An article by the Agency for Science on research being conducted to harness body heat in order to power electronics.

45 Common Foods and the Number of Calories They Contain

This HowStuffWorks article covers commonly eaten foods and how many calories they contain.
 

References

Ashcroft, N., & Mermin, D. (1976). Solid state physics. Holt, Rinehart and Winston.

Johnson-Silvers, J. (2016). eDrink mug and hollow flashlight: Alumna Ann Makosinski’s new inventions. Society for Science & the Public.

Knight, R. (2017). Physics for scientists and engineers: A strategic approach (4th ed.). Pearson.

Ogin, G. (n.d.) How much heat per hour do humans dissipate? PhysLink.com.