Embedded Files
Lesson overview
Lesson overview
Watch the video to learn more about the activities.
Challenges
Challenges
Challenges
Challenges
Some of the activities in this lesson are must do activities. These are also called a mini challenge. Please have a go at the should do activities and reach out to your teacher if you need assistance. You could also spend some extra time problem solving a solution to these challenges. Finally, there are super challenge activities, the could do activities. We strongly encourage you to try these.
Activity 1 - Determining the speed of light
Activity 1 - Determining the speed of light
Read the passage carefully.
How can we measure the speed of light?
Since all electromagnetic radiation travels at the same speed we can use another form of electromagnetic radiation, of a known frequency and easily available in our homes. Microwaves.
You are going to complete a first-hand investigation, using a microwave, to estimate the speed of light.
You can use any available microwaveable materials which will safely melt or change appearance when heated by the microwave. Examples include a big block of chocolate, a mars bar, egg whites spread over a plate, marshmallows lined up or a big cheese slice.
On the rear of the microwave will be the manufacturer label which specifies the operating frequency of the device. A typical value is 2.45GHz (2450MHz), however this can vary between some brands. The frequency must be converted to Hertz:
1GHz = 1,000,000,000Hz
1MHz = 1,000,000Hz
The microwave’s rotating plate needs to be removed for this activity as uneven heating of the material is needed to observe a suitable result. A microwave safe plate is placed in the microwave to hold the selected material for this activity.
The selected material can be heated in the microwave for 10 seconds. Depending on the material and the power of the microwave, this may need to be adjusted to longer or shorter times until small marks (these can be soft or melted spots) from the spot heating can be clearly and separately observed.
These soft or melted spots represent the wave nodes of the microwave electromagnetic radiation.
As in the image the wavelength is double the distance between two adjacent nodes.
Are there any words from the passage above that you are unsure of?
Using your research from above, complete the following table. Select the button, then select Use Template.
Now let’s show some evidence of your experiment.
In your workbook, draw the following table.
Post two pictures below and explain or label them.
Here is an example: Using a chocolate bar, on a plate in the microwave. Where it melts is a node.
Now, let's do some maths to calculate the speed of light. Record this in your workbook.
Follow these steps closely:
Distance between nodes (or melted spots) in your experiment = m
(Hint: use the image above to understand this, remember the units)
The wavelength is double the distance between adjacent nodes (in meters).
Wavelength = m
The frequency is that of the microwave (in hertz) determined from the actual microwave.
(hint: Multiply a value in MHZ by 1000 000 to get hertz)
Frequency = hertz
speed of the wave = wavelength x frequency
speed of the wave = x meters per second (ms-1)
= meters per second (ms-1)
Compare your calculated value to the accepted value of 299,792,458ms-1 from NIST.
Determine your accuracy, as a percentage, by doing the following calculation:
Calculated value ÷ true value x 100%
= %
CONGRATULATIONS!
You have just (hopefully reasonably closely) calculated the fastest thing in the universe…absolute cosmic speed…the speed of light.
Can you propose reasons for the difference between your result and the accepted value?
Activity 2 - Super duper challenge
Activity 2 - Super duper challenge
The links to Science Buddies and The Wonders of Physics outline the procedures for this “Speed of Light” experiment. Using them and the previous information undertake an investigation to compare two different substances used in the microwave to calculate the speed of light.
Complete the scientific investigation worksheet to the right. Select the button and then select Use Template to make a copy for yourself.
Handing in your work
Handing in your work
Don't forget to hand in the work you completed today!
Your teacher will have told you to do one of the following:
Upload any digital documents you created and any photos you took of your written work to your Learning Management system (MS Teams, Google Classroom for example).
Email any digital documents you created and any photos you took of your written work to your teacher.
Make sure you keep any hand written work you did in your exercise book or folder as your teacher may need to see these when you are back in class.
Student reflection
Student reflection
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