Problem 2139 - JEE Physics

Question

Our eyes respond to wavelength ranging from (A) \(400 \mathrm{~nm}\) to \(700 \mathrm{~nm}\) (B) \(-\infty\) to \(+\infty\) (C) \(1 \mathrm{~mm}\) to \(700 \mathrm{~nm}\) (D) \(700 \mathrm{~nm}\) to \(800 \mathrm{~nm}\)

Step-by-Step Solution

Answer

The correct range of wavelengths to which our eyes respond is (A) \(400 \mathrm{~nm}\) to \(700 \mathrm{~nm}\), which corresponds to the visible light spectrum.

Step 1: Recall the range of wavelengths for visible light

Visible light is a part of the electromagnetic spectrum and corresponds to a certain range of wavelengths. The visible light spectrum ranges from \(400 \mathrm{~nm}\) (violet) to \(700 \mathrm{~nm}\) (red).

Step 2: Evaluate the given options

Now, let's go through each option and decide if it matches the correct range of wavelengths to which our eyes respond: (A) \(400 \mathrm{~nm}\) to \(700 \mathrm{~nm}\): This option corresponds to the visible light spectrum, which is the range of wavelengths to which our eyes respond. (B) \(-\infty\) to \(+\infty\): This option represents an infinite range of wavelengths, which is not specific to visible light. Our eyes cannot respond to an infinite range of wavelengths. (C) \(1 \mathrm{~mm}\) to \(700 \mathrm{~nm}\): This option includes wavelengths beyond the visible light spectrum, which are not detected by the human eye. (D) \(700 \mathrm{~nm}\) to \(800 \mathrm{~nm}\): This option represents a range of wavelengths within the infrared region, which is not part of the visible light spectrum and cannot be detected by the human eye.

Step 3: Select the correct option

Option (A) represents the visible light spectrum, which is the range of wavelengths to which our eyes respond. Therefore, the correct answer is (A) \(400 \mathrm{~nm}\) to \(700 \mathrm{~nm}\).

Key Concepts

Wavelengths of Visible Light

The visible light spectrum consists of a particular range of wavelengths perceptible to the human eye. This range stretches from approximately 400 nanometers (nm) to 700 nm, where each wavelength corresponds to a different color that we can see.
At the lower end of the spectrum, around 400 nm, we observe violet, transitioning through blue, green, yellow, and finally to red at around 700 nm.
Because visible light is only a small part of the electromagnetic spectrum, most wavelengths are invisible to us.
For example:

• Violet: ~400 nm
• Blue: ~450 nm
• Green: ~500 nm
• Yellow: ~570 nm
• Orange: ~590 nm
• Red: ~620-700 nm

Understanding the wavelengths of visible light helps us grasp why different objects appear in different colors depending on how they reflect or emit light in this range.

Electromagnetic Spectrum

The electromagnetic spectrum is a vast range of wavelengths that includes not just visible light, but also other types of waves such as radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays.
Each type of wave is characterized by its wavelength and frequency. It's important to understand that visible light is only a small fraction of the electromagnetic spectrum, specifically between 400 nm and 700 nm.
Here's a quick breakdown of the electromagnetic spectrum's major components:

• Radio waves: long wavelengths, can be longer than a football field!
• Microwaves: used in radar and cooking, slightly shorter.
• Infrared: just beyond red in the visible spectrum, felt as heat.
• Ultraviolet: beyond violet, known to cause sunburns.
• X-rays: much shorter wavelengths, penetrate materials, used in medical imaging.
• Gamma rays: shortest wavelengths, very energetic, emerge from nuclear reactions.

Understanding the electromagnetic spectrum helps us appreciate the variety of electromagnetic waves and their applications in everyday life.

Human Eye Response to Light

Human eyes are designed to detect light within the visible spectrum. This response is due to photoreceptor cells located in the retina, specifically rods and cones.
Cones are responsible for color vision and function best in bright light. They are sensitive to three regions of the visible spectrum, corresponding to blue (short), green (medium), and red (long) wavelengths.
On the other hand, rods are more sensitive to light, aiding in night vision but do not contribute to color vision as they are not sensitive to color.

• Rods: function in low light, monochrome vision.
• Cones: function in bright light, detect colors (red, green, and blue sensitivity).

The human eye's response to visible light enables us to perceive a colorful world, differentiating objects and their surroundings based on color and brightness.