Warning Signals and Eye Sensitivity – Rankers Physics

Lens Makers Formula/ Len's Formula: Practice Problem & Solution

Assertion (A): Warning signals installed at the top of tall buildings and monuments employ red light. Reason (R): Human eye is most sensitive to red colour.  
Both (A) & (R) are true and the (R) is the correct explanation of the (A)
Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(A) is true but (R) is false
Both (A) and (R) are false

Short Solution (Best for NEET):

To solve this problem, we apply the core principles of Lens Makers Formula/ Len's Formula. Understanding the underlying formula is key to arriving at the correct answer below:

Red light has the longest wavelength and scatters least, making it visible from a distance. Thus, (A) is true. However, the human eye is most sensitive to yellow-green light (approximately \(555\text{ nm}\)), not red. Thus, (R) is false. So, (A) is true but (R) is false.

Leave a Reply

Your email address will not be published. Required fields are marked *

Similar Practice Questions

Explore conceptually related problems to test your knowledge.

1. A microscope is focused on a mark on a piece of paper and then a slab of glass of thickness $3 cm$ and refractive index $1.5$ is placed over the mark. How should the microscope be moved to get the mark in focus again? (2006)
2. Assertion (A): Secondary rainbow is fainter than primary rainbow. Reason (R): Secondary rainbow is seen due to the scattering of primary rainbow through water molecules.  
3. A convex lens is made up of three different materials as shown in the figure. For a point object placed on its axis, the number of images formed are :
4. Exposure time of camera lens at f/2.8 setting is 1/200 second. The correct time of exposure at f/5.6 is (1995)
5. Assertion (A): The speed of light in an optically rarer medium is greater than that in an optically denser medium. Reason (R): One light year equals to \(9.5 \times 10^{12}\), km.