What color do we see when electric and magnetic fields in our eyes oscillate at 400 trillion times per second?

What color do we see when electric and magnetic fields in our eyes oscillate at 400 trillion times per second?

• A. Red
• B. Yellow
• C. Green
• D. Blue

Answer: (A)

The color you see is determined by the wavelength of the visible light and how our eye’s cones respond to different wavelengths. A frequency of 400 trillion cycles per second (4.0×10^14 Hz) corresponds, with the relation λ = c/f, to a wavelength of about 750 nanometers. That places it at the long-wavelength end of the visible spectrum, right at the red region. So light oscillating at that rate is perceived as red by our eyes. If the wavelength were shorter, you’d get colors like orange or green; longer would be infrared and not visible at all.

The color you see is determined by the wavelength of the visible light and how our eye’s cones respond to different wavelengths. A frequency of 400 trillion cycles per second (4.0×10^14 Hz) corresponds, with the relation λ = c/f, to a wavelength of about 750 nanometers. That places it at the long-wavelength end of the visible spectrum, right at the red region. So light oscillating at that rate is perceived as red by our eyes. If the wavelength were shorter, you’d get colors like orange or green; longer would be infrared and not visible at all.