Question

Select the sentences about the physical nature of light that are true. Check all that apply. Check all that apply. Blue light has a wavelength of 750 nm, the longest wavelength of visible light, and red has a wavelength of 500 nm. Light is electromagnetic radiation, a type of energy embodied in oscillating electric and magnetic fields. The units of frequency are distance per second. The more closely spaced the waves, that is, the longer the wavelength, the more energy there is. Grass appears green because it reflects primarily the wavelength associated with green light and absorbs the others. Light in a vacuum travels at 3.00×108mph. Electromagnetic radiation can be characterized by wavelength, amplitude, and frequency. The presence of a variety of wavelengths in white light is responsible for the way we perceive colors in objects.

Answer 1

Correct options:

- Blue light has a wavelength of 750 nm, the longest wavelength of visible light, and red has a wavelength of 500 nm. --> FALSE. It's actually the opposite: blue light has a wavelength of approx. 500 nm, while red has a wavelength of 750 nm, the longest wavelength of visible light.

- Light is electromagnetic radiation, a type of energy embodied in oscillating electric and magnetic fields. --> TRUE. Electromagntic radiation is a type of transverse waves, consisting of electric and magnetic fields oscillating perpendicularly to each other.

- The units of frequency are distance per second. --> FALSE. Frequency is measured in Hertz (Hz), which corresponds to 1/seconds ($s^{-1}$.

- The more closely spaced the waves, that is, the longer the wavelength, the more energy there is. --> FALSE. The energy of an electromagnetic wave is inversely proportional to the wavelength:

$E=\frac{hc}{\lambda}$

that means, the longer the wavelength, the less energy there is.

- Grass appears green because it reflects primarily the wavelength associated with green light and absorbs the others. --> TRUE. The color of the objects as we see them corresponds to the color they reflect, while all the other colors are absorbed by the object.

- Light in a vacuum travels at 3.00×108mph. --> FALSE. The units are wrong: the speed of light in a vacuum is $3.00\cdot 10^8 m/s$.

- Electromagnetic radiation can be characterized by wavelength, amplitude, and frequency. --> TRUE. Wavelength is the distance between two consecutive crests, amplitude is the maximum displacement of the wave relative to the equilibrium position, frequency is the number of oscillations per second.

- The presence of a variety of wavelengths in white light is responsible for the way we perceive colors in objects. --> TRUE. White light consists of many different colors, and depending on which of them are absorbed/reflected by the objects, we perceive them in different ways.