Consider the electromagnetic radiations having wavelengths 200 nm, 500 nm and 1000 nm. Which wavelength (s) of the following can make visual sensation to a human eye?
500 nm only
Understanding Visible Light Wavelengths
The question asks which of the given electromagnetic radiations, with wavelengths 200 nm, 500 nm, and 1000 nm, can cause visual sensation in a human eye. Visual sensation is caused by light that falls within the visible spectrum.
The Visible Light Spectrum
The visible light spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. It is typically defined by wavelengths ranging from approximately 380 nanometers (nm) to 750 nanometers (nm). Different wavelengths within this range correspond to different colors, from violet (shorter wavelengths) to red (longer wavelengths).
Analyzing the Given Wavelengths
Let's examine each of the given wavelengths and compare them to the visible spectrum range (380 nm to 750 nm):
- Wavelength 1: 200 nm
This wavelength is 200 nm.
Comparing to the visible range (380-750 nm), 200 nm is significantly shorter than 380 nm.
Electromagnetic radiation with wavelengths shorter than violet light (typically < 380 nm) is known as ultraviolet (UV) radiation. Human eyes cannot see UV radiation.
Therefore, 200 nm cannot cause visual sensation.
- Wavelength 2: 500 nm
This wavelength is 500 nm.
Comparing to the visible range (380-750 nm), 500 nm falls comfortably between 380 nm and 750 nm.
Wavelengths around 500 nm typically correspond to the color green or blue-green in the visible spectrum.
Therefore, 500 nm can cause visual sensation.
- Wavelength 3: 1000 nm
This wavelength is 1000 nm.
Comparing to the visible range (380-750 nm), 1000 nm is significantly longer than 750 nm.
Electromagnetic radiation with wavelengths longer than red light (typically > 750 nm) is known as infrared (IR) radiation. Human eyes cannot see IR radiation.
Therefore, 1000 nm cannot cause visual sensation.
Summary of Wavelengths and Visibility
We can summarize the analysis in the table below:
| Wavelength (nm) | Falls within 380-750 nm? | Visible to Human Eye? |
|---|---|---|
| 200 | No (< 380 nm) | No (Ultraviolet) |
| 500 | Yes (between 380 and 750 nm) | Yes (Visible Light) |
| 1000 | No (> 750 nm) | No (Infrared) |
Conclusion
Based on the analysis, only the electromagnetic radiation with a wavelength of 500 nm falls within the visible light spectrum that can be detected by the human eye and cause a visual sensation. The wavelengths 200 nm (ultraviolet) and 1000 nm (infrared) are outside the visible range.
Revision Table: Electromagnetic Spectrum and Vision
| Region | Approximate Wavelength Range | Visible to Humans? | Example Use/Effect |
|---|---|---|---|
| Gamma Rays | < 0.01 nm | No | Medical imaging, sterilization |
| X-rays | 0.01 nm - 10 nm | No | Medical imaging, security scanning |
| Ultraviolet (UV) | 10 nm - 400 nm | No | Sunburn, sterilization lamps |
| Visible Light | 400 nm - 750 nm | Yes | Sight, photography, lighting |
| Infrared (IR) | 750 nm - 1 mm | No | Heat radiation, thermal imaging |
| Microwaves | 1 mm - 1 meter | No | Cooking, communication (Wi-Fi, mobile) |
| Radio Waves | > 1 meter | No | Broadcasting (radio, TV), communication |
Additional Information on Visible Light Sensation
The human eye contains photoreceptor cells called rods and cones in the retina. Cones are responsible for color vision and function best in bright light, while rods are responsible for vision in low light conditions but do not perceive color. These photoreceptors contain pigments that absorb light photons. When photons of visible light within the appropriate wavelength range hit these pigments, they trigger a series of chemical and electrical signals that are sent to the brain via the optic nerve. The brain then interprets these signals as visual images and colors. The ability to perceive specific wavelengths as different colors (like 500 nm as green/blue-green) is a complex process involving the different types of cone cells, each sensitive to different parts of the visible spectrum (red, green, and blue light).
The electromagnetic spectrum includes a wide range of radiation types, but only a very narrow band is detectable by the human eye. The sensitivity of the eye varies across the visible spectrum, being generally highest in the green-yellow region (around 550 nm).
The speed of all electromagnetic waves, including visible light, in a vacuum is the speed of light, denoted by \(c\), which is approximately \(3 \times 10^8\) meters per second. The relationship between the speed of light (\(c\)), wavelength (\(\lambda\)), and frequency (\(f\)) is given by the formula: \(c = \lambda f\).
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