Experiment 3: Measuring the Speed of Light Using a Microwave Oven
Introduction
While the speed of light is a fundamental constant in physics, it can be
measured using common household appliances. This experiment uses a
microwave oven and food items to calculate the speed of light based on the
wavelength of microwaves.
Objective
To calculate the speed of light by measuring the wavelength and frequency of
microwaves in a standard microwave oven.
Materials Needed
Microwave oven
Microwave-safe dish
Marshmallows or a bar of chocolate
Ruler or measuring tape
Calculator
Notebook and pen
Procedure
1. Preparing the Microwave
o Remove the turntable to keep the food stationary. Alternatively,
immobilize it so it doesn't rotate.
2. Conducting the Experiment
o Spread the marshmallows or lay the chocolate bar evenly on the
microwave-safe dish.
o Place the dish in the microwave.
o Heat on low power until you see spots melting (approximately 10-
20 seconds).
3. Measuring Wavelength
o Quickly remove the dish and observe the pattern of melted spots.
o Measure the distance between two adjacent melted spots. This
distance is half the wavelength (λ/2\lambda/2λ/2) of the
microwave radiation.
o Multiply this distance by 2 to get the full wavelength (λ\lambdaλ).
4. Calculating Frequency
o Locate the frequency (fff) of your microwave oven, usually stated
in the manual or at the back of the unit (commonly around 2,450
MHz).
5. Calculating the Speed of Light
o Use the formula: c=f×λc = f \times \lambdac=f×λ Where ccc is the
speed of light.
o Ensure units are consistent (convert MHz to Hz and centimeters to
meters).
Example Calculation
Measured distance between melted spots: 6 cm
Wavelength: 6 cm×2=12 cm=0.12 m6\,\text{cm} \times 2 = 12\,\text{cm}
= 0.12\,\text{m}6cm×2=12cm=0.12m
Frequency: 2,450 MHz=2.45×109 Hz2,450\,\text{MHz} = 2.45 \times
10^9\,\text{Hz}2,450MHz=2.45×109Hz
Speed of light: c=2.45×109 Hz×0.12 m=2.94×108 m/sc = 2.45 \times
10^9\,\text{Hz} \times 0.12\,\text{m} = 2.94 \times
10^8\,\text{m/s}c=2.45×109Hz×0.12m=2.94×108m/s
Data Analysis
Compare your calculated value with the accepted speed of light
(3.00×108 m/s3.00 \times 10^8\,\text{m/s}3.00×108m/s).
Discuss possible sources of error, such as measurement inaccuracies or
uneven heating.
Safety Precautions
Be careful when handling hot items.
Do not run the microwave empty, as it can damage the appliance.
Conclusion
This experiment demonstrates a fundamental astrophysical constant using
simple kitchen equipment, bridging everyday experiences with cosmic
principles.
