Report Copyright Infringement View in OSM UK

Description

Experiment with melting chocolate to learn about the speed of light.

Resources

Microwave
Pens or pencils
A4 paper
Rulers
Calculator or phone
Microwavable bowl
Microwavable plate
Heatproof worktop or surface protector
Oven gloves
110g or 120g bar of chocolate, enough for one per group

Instructions

Planning and setting up the activity

-Remember to give a safety briefing for the cooking equipment and methods you’re using. You may wish to demonstrate the methods or activity before you all start cooking.
-Be aware of anyone with Bluetooth medical devices, as being near to turned-on microwaves may cause interference.
-Remove the turnstile plate and wheels from the microwave and place them somewhere safe.
-Place a bowl upside down in the microwave to rest the plate on.
-Put the pens, paper, ruler, calculator, chocolate bar and plate on a table, enough for one set per group.
-Make sure to have a heatproof surface to place the hot plate on, such as a worktop protector or trivet.

Running the activity

1.Gather everyone together and ask if anyone knows what the speed of light is. Make sure to explain what it is, how it can be measured and how it can be tested. We’ve included some information on this page that you can use.

2. Explain that you’ll be learning about the speed of light by melting chocolate. In groups, you’ll be using the microwave to slightly melt their chocolate. Each group will then measure the spaces between the melted spots on the chocolate bar and complete the calculation to work out the speed of light.

3. Everyone should get into groups, with each group at a different table.

4. Ask each group to unwrap and place their chocolate bar on their plate. Make sure there’s no metal or foil wrappers and no metal on the plate, as this metal can’t go in the microwave.

5. The group’s who are waiting could be doing another supervised science activity.

6.The first group should place their chocolate into the microwave. Ask them to place the plate on top of the up-turned bowl and run the microwave for 20 seconds.

7. When the microwave stops, use the oven gloves to take the plate out of the microwave and place it on a heatproof surface.

8. Ask everyone to look for melted spots on the chocolate bar.

9.If there are melted spots, they can take their chocolate bar back to their table.

10. If there are no melted spots, put it back in for another 20 seconds and repeat until there are melted spots, making sure not to burn the chocolate.

11. After the group get back to their table, they should measure the distance between two of the melted spots. If there are more than two melted spots, take several measurements and find the average between the pairs.

12. Explain that the distance between melted spots is part of a microwave wave – it's half a wavelength. Scientists use this to figure out how fast light travels.

13. Multiply your measurement by two to get the full wavelength and note this down.

14. Now, use the formula: Speed of Light = Wavelength × Frequency

15. Convert your wavelength from centimetres to metres (so divide by 100), then multiply by 2,450,000,000. The frequency of microwaves in most ovens is 2,450,000,000 Hz (or 2.45 GHz).

16. The actual speed of light is 299,792,458 metres per second (m/s). How close was your result?

17. After they’ve finished their experiment, you could melt the chocolate and make hot chocolate spoons.

Tags

(none)

Badge Links

• Space - Light