How to play Antenna Workshop
- Choose a test and read the frequency on the card: MHz means 10⁶ Hz, GHz means 10⁹ Hz.
- Use λ = c ÷ f with c = 3 × 10⁸ m/s; an antenna is λ ÷ 4, and oven hot spots are λ ÷ 2 apart.
- Type your prediction and press Start. The waves play slowed down by their own frequency.
- Compare the orange marks with the crests, the antenna, or the melted spots, and with the ladder on the right.
Waves you can't see
Radio, television, mobile phones, Wi-Fi, microwave ovens, and light are all electromagnetic waves: ripples in electric and magnetic fields that need no medium and all travel at the speed of light, c = 3 × 10⁸ m/s. What makes them different is their frequency, and so their wavelength, λ = c ÷ f. An AM station at 1 MHz sends waves 300 m long; FM radio at 100 MHz, 3 m; Wi-Fi at 2.4 GHz, 12.5 cm; visible light has wavelengths of about half a millionth of a metre. Antennas are sized to match: a simple rod a quarter of a wavelength long resonates with the wave, which is why car antennas are under a metre and AM masts are tens of metres tall. In a microwave oven the waves bounce back and forth between the metal walls and set up a standing wave, with hot spots half a wavelength apart and cooler spots in between. That's why the food turns on a turntable, and why a chocolate bar left still melts in spots you can measure.
A focused learning model
Waves travel at exactly 3 × 10⁸ m/s (in air, light is a tiny bit slower). Each wave is slowed down by its own frequency, so one oscillation lasts one second on screen; the wave leaves the antenna and nothing reflects. In the oven, the standing wave is perfect and the hot spots sit exactly half a wavelength apart. Answers within 2% are right.