Photometry is the branch of physics that deals with the measurement of light as perceived by the human eye. It focuses on understanding and quantifying how humans see and interact with light. Chapter 22 of HC Verma's Concepts of Physics introduces students to the basics of photometry, along with key concepts like luminous intensity, luminous flux, and brightness.
This chapter covers several essential concepts that help students grasp the fundamentals of light measurement. Here are the major topics:
I ∝ 1/r².To solve problems in photometry, you will need to understand and use these important formulas:
I = Φ / Ω, where Φ is the luminous flux and Ω is the solid angle in steradians.E = Φ / A, where Φ is the luminous flux and A is the area.E = I / r², where I is the luminous intensity and r is the distance from the source.The problems in HC Verma's Chapter 22 are designed to help students apply these concepts and develop a deeper understanding. Below are examples of typical problems and their solutions:
Problem: A point light source emits 1000 lumens of luminous flux uniformly in all directions. Calculate the illuminance at a distance of 2 meters from the source.
Solution:
Φ = 1000 lumens.E = Φ / (4πr²), where r = 2 meters.E = 1000 / (4 × 3.1416 × 2²) ≈ 19.89 lux.Problem: A light source emits luminous flux of 500 lumens uniformly across a solid angle of 2 steradians. Find the luminous intensity.
Solution:
Φ = 500 lumens.I = Φ / Ω, where Ω = 2 steradians.I = 500 / 2 = 250 cd.Photometry has numerous practical applications, including:
HC Verma is widely regarded as one of the best books for understanding physics concepts for Class 11 and Class 12. Here’s why you should practice Chapter 22 problems:
The photoelectric effect can be used to quantify the intensity of light using a photon, which is an elementary particle. When a photon absorbs and ejects an electron, it performs work.
Photometry is crucial in a variety of domains, including physics, astronomy, and technology. It aids in the identification of various light sources as well as the measurement of their intensities. Photometry has been used to calibrate light measurement devices.