Area: Math, Physics and Design Technology (DT)

Grade Level: Any secondary level

Course: Multidisciplinary Lesson

Timeframe: 45 minutes – 1 hour

Lesson Overview

Students investigate how parabolas can focus light to heat marshmallows in a simple solar oven. This is one way that people could cook in the powerless world or if they have limited access to cooking fuels. This activity can be done in small groups of 3 or more individuals.


Upon completion of this Lesson students will be able to:

  • Math: understand the geometry and potential real world uses of parabolas
  • Physics: understand how solar energy can be used and how light energy can be converted into heat energy
  • Design and Technology: use basic resources to engineer a simple solar oven

Material/ resources

This activity works best outside on a sunny day. On a cloudy day, perform the experiment inside the classroom with a halogen desk lamp. This could perhaps also be used as a demonstration on a sunny day before going outside.

  1. printed copies of the parabola (template provided)
  2. A4 corrugated cardboard (four sheets per group)
  3. A3 thin card (one sheet per group)
  4. aluminium foil
  5. glue sticks, tape
  6. long bamboo or wood skewers
  7. marshmallows
  8. probe or infra-red thermometer
  9. protective gloves
  10. transparent acrylic sheet (optional)
  11. halogen desk lamps for use on a cloudy day (caution: can be hot)

Lesson activities

  • Imagine a world where there is no electricity or access to fuels for cooking.
  • What potential ways could you use to cook food or to heat water?
  • One solution that could be used is solar cooking, in this case we will focus on the concept of a parabolic solar oven.
  • Discuss which STEAM roles might help in this situation: e.g. optical engineer, thermodynamics scientist, energy engineer, food scientist etc. Students can take on these roles if they wish.
  • Briefly introduce parabolas and their properties.
  • A parabola is a curve where any point is at an equal distance from a fixed point (the focus), and a fixed straight line (the directrix).f
  • Use the link for a more detailed explanation and diagrams Solar Snacks
  • Explain that parabolas are found everywhere in the world including;
    • In nature
      Solar Snacks
    • In Architecture
      Solar Snacks Solar Snacks
    • In everyday life they are especially useful for reflecting and focusing light in torches, vehicles headlights and household light bulbs.
      Solar Snacks
  • Guide teams as they carefully follow the step-by-step instructions to build a small reflective parabolic solar oven.
  • If undertaking this outside, students can optionally use transparent acrylic sheets as a top cover, which helps trap heat. *Do NOT try this if using halogen lamps*.
  • Step-by-step instructions for learners
    1. Cut out a parabola using the template page provided
    2. Use this parabola as a template to draw a parabola shape onto each of the 4 sheets of A4 corrugated cardboard and then cut the shapes out (leaving each group with 4 individual parabolas made of corrugated cardboard)
    3. Glue two of the parabolas together to create one of double thickness, then do the same with the other two parabolas as well
    4. Use a skewer to accurately create a hole through the focus points on each of the 2 parabolas (again using the parabola template with the focus point marked as a red spot)
    5. Use the glue stick to carefully cover one side of the A3 thin card, and one side of each parabola, with aluminum foil. Make sure the shiny side faces out and try not to create wrinkles as this will reduce the effectiveness of the reflective surfaces
    6. Wrap the thin card around the curved edges of the parabolas and tape it in place to create your solar oven, this should be wrapped all-round the parabola at each end to form a kind of a parabolic trough.
      Solar Snacks
    7. Slide a skewer through the pre-pierced focus points of each parabola and make sure the skewer passes straight through the oven and out each side
    8. Now they have engineered a simple reflective parabolic solar oven with a cooking skewer
  • Test the parabolic solar ovens with marshmallows and thermometers. See how fast the marshmallows melt, and / or what final temperature the ovens reach.
  • Step-by-step instructions for learners
    • It’s time to cook! Load one or two marshmallows onto your skewer. Make sure they don't touch the foil, so light can reflect onto them
    • Angle your oven to face the sun, or if inside, the halogen lamp
    • *NOTE: Take extra care if using a halogen lamp as they can generate a lot of heat and you could burn yourself. Use protective gloves and wear protective eyewear*.
      *The following image below omits one side of the card/foil reflector*
      Solar Snacks
    • It is important to explain the process that is happening, solar energy, in the form of sunlight is being converted into heat energy to heat and ‘cook’ the marshmallows.
    • The principles of the process are;
      1. Concentrating sunlight: the reflective metal surface is reflecting the sunlight so that it is concentrated and the energy is stronger at the focus point where the skewer and marshmallows are located
      2. Converting light energy to heat energy: the interaction between the light energy and the receiver materials converts light to heat and this is called conduction
      3. Trapping heat energy: this heat energy is now being ‘trapped’ within the parabolic trough and as more light energy enters it will continue to be converted into heat energy, this process can be increased by covering the top of the parabolic oven with the transparent acrylic sheet.
    • • The parabolic solar oven lets the UV light rays in and then converts them to longer infrared light rays. Infrared radiation has the right energy to make water, fat and protein molecules in food vibrate vigorously and heat up.
    • It is not the sun’s heat that cooks the food, nor is it the outside ambient temperature (though this can affect the rate or time required to cook) but rather it is the sun’s rays that are converted to heat energy that cook the food.

Once all the groups have completed the task and tested their ovens the teacher will decide which group’s oven worked the best based on the temperature it achieved and / or the level in which their marshmallows were cooked.

Instructions for teachers:

Interesting facts about parabolas

  • A parabola is plane curve which is mirror-symmetrical and is approximately U-shaped, the mathematical equation is y2 = 2px or x2 = 2py
  • If you throw a ball, the trajectory it follows through the air is a parabola
  • Any ray of light that’s parallel to the parabola’s axis of symmetry will be reflected onto the focus point. That’s why parabolas are used to focus torch or headlight beams and are also used in satellite dishes.

Differentiation Ideas

Support: Make one model for students to copy prior to the session

Challenge: Ask teams to also make ovens based around hemispheric end formers and compare their performance. Discuss why the parabola works better: the shape focuses the light onto the axis, where the marshmallows are positioned. A hemisphere can’t focus the light in the same way.

Additional prompts for participating students

  • Use the foil shiny side out and take care not to wrinkle it when gluing to the card.
  • Don’t forget to coat the two end former parabolas in foil as well.
  • It’s important that as much light as possible can get below the marshmallows, which should be in small enough pieces so that they don’t touch the foil trough.
  • Angle the ovens so that they point at the sun or the lamp being used.
  • The red dot on the parabola template is the focus point – the axis on which the skewer will go and on which the marshmallows will need to be.
  • Light needs to reflect off the parabola and trough lining onto the marshmallows and that's vital for an efficient cooking process.
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