41:04 - Dara O'Briain works out the speed of light by making cheese on toast.
speed of light = frequency x wavelength
frequency (from back of microwave) = 2450 MHz = 2.45 x 109 giga hertz
calculated speed of light = 0.13m x 2.45 x109 = 3.2 x 108 m/s
Actual speed of light is 3.0 x 108 m/s (300,000 km/s=3 x 105 km/s)
Pretty close, eh!