A 200 W sodium street lamp emits yellow light of wavelength 0.6 µm

⇦

⇨

A 200 W sodium street lamp emits yellow light of wavelength 0.6 µm. Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is

Options

(a) 1.5 x 10²⁰
(b) 6 x 10¹⁸
(c) 62 x 10²⁰
(d) 3 x 10¹⁹

Correct Answer:

1.5 x 10²⁰

Explanation:

Give that, only 25% ov 200 W converter electrical energy into light of yellow colour
(hc / λ) x N = 200 x 25/100
Where N is the no. of photons emitted per second, h = plank’s constant, c, speed of light
N = 200 x 25 / 100 x λ / hc
= 200 x 25 x 0.6 x 10⁻⁶ / (100 x 6.2 x 10⁻³⁴ x 3 x 10⁸)
= 1.5 x 10²⁰

Related Questions:

1. If the sodium light in Young’s double slit experiment is replaced by red light
2. Which of the following atoms has the lowest ionisation potential?
3. A transverse wave is represented by y = a sin (?t – kx)
4. A body cools in 7 minute from 60⁰C to 40⁰C. What time, in minute does it take to cool
5. The moment of inertia of a thin circular disc about an axis passing through its centre

Topics: Dual Nature of Matter and Radiation (150)
Subject: Physics (2479)

---

Important MCQs Based on Medical Entrance Examinations To Improve Your NEET Score

18000+ students are using NEETLab to improve their score. What about you?

Solve Previous Year MCQs, Mock Tests, Topicwise Practice Tests, Identify Weak Topics, Formula Flash cards and much more is available in NEETLab Android App to improve your NEET score.

---

Share this page with your friends