Question

The visible spectrum includes light that ranges from about ________. a. \(400-700 \mathrm{nm}\) b. \(200-900 \mathrm{nm}\) c. \(20-20000 \mathrm{Hz}\) d. \(10-20 d B\)

Short answer

The visible spectrum includes light that ranges from about \(400-700 \mathrm{nm}\).

Step-by-step solution

Understanding the Options

Look at the answer options provided. They fall into different units of measurement and represent different parts of the electromagnetic spectrum.

Identifying the Right Unit of Measurement

Remember, the range of the visible spectrum is usually measured in nanometers (nm). So, the options \(20-20000 \mathrm{Hz}\) and \(10-20 d B\) can be eliminated since they do not use the correct units.

Identifying the Right Range

The remaining options are \(400-700 \mathrm{nm}\) and \(200-900 \mathrm{nm}\). Recall that the visible spectrum is typically in the range of about \(400-700 \mathrm{nm}\). Thus, the correct answer is option a. \(400-700 \mathrm{nm}\)

Key concepts

Electromagnetic Spectrum

The electromagnetic spectrum is an umbrella term used to describe the entire range of electromagnetic waves in order of increasing frequency and decreasing wavelength. This ranges from the very long wavelengths, like radio waves, to the extremely short ones, such as gamma rays. Each type of electromagnetic wave has unique properties and uses, covering both invisible and visible parts of the spectrum. The visible spectrum, which is the focus of this discussion, makes up only a small portion of the entire electromagnetic spectrum.
It comprises light waves that we can see with our naked eyes. Other parts of the spectrum, such as ultraviolet or infrared, are not visible to humans. Everything from the colors we see in a rainbow to the detailed images captured by cameras fits within this narrow band of visible light.

• Wavelengths determine how these waves are categorized.
• Each type of wave on the electromagnetic spectrum travels at the speed of light, approximately 299,792 kilometers per second in a vacuum.

Nanometers

Nanometers are used as a unit of measure to express the wavelength of light, particularly in the visible spectrum. One nanometer (nm) is one billionth of a meter. The choice of nanometers is particularly useful in dealing with the very small wavelengths of light waves, which fall in the range of hundreds of nanometers.
Given that the visible spectrum stretches from about 400 to 700 nm, it illustrates the limits of human vision within the broader electromagnetic spectrum. This portion of the spectrum encompasses all the colors visible to the human eye.

• 400 nm is where violet light appears.
• 700 nm marks the end of visible red light.

Understanding these measurements is key in fields such as optics and physics, where precise calculations are essential for developing technologies like lasers, microscopes, and optical fibers.

Light Waves

Light waves are a form of electromagnetic radiation that is visible to the human eye. These waves exhibit properties that are both electric and magnetic, hence the term "electromagnetic." Light can be described as both a wave and a stream of photons, which are particles of energy.
The color of light depends on its wavelength. Shorter wavelengths correspond to violet and blue light, while longer wavelengths correspond to red and orange light. The behavior of light waves helps in understanding many phenomena such as reflection, refraction, and diffraction.

• Light travels in straight lines but can bend or change direction when it hits different media.
• It's crucial for vision and is used in various technologies like cameras and visual displays.

Range of Visibility

The range of visibility refers to the portion of the electromagnetic spectrum that is detectable by the human eye. This range is typically between 400 and 700 nanometers, encompassing all the colors seen in a typical rainbow.
Each color within this range corresponds to light of a particular wavelength:

• Violet is visible around 400 nm.
• Blue and green are next, transitioning to yellow.
• Red is visible at the longer wavelengths, around 700 nm.

Anything outside this wavelength range, such as ultraviolet or infrared light, is invisible to humans. However, certain animals and instruments can detect these other kinds of light. This understanding is crucial not only in physics and optics but also in technology design, ensuring that devices optimally use the light humans can see.