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. The radius of a ball is(5.2±0.2)cm.The percentage error in the volume of the ball
2. A charged particle with a velocity 2×10³ ms⁻¹ passes undeflected through electric field
3. Three objects coloured black, gray and white can withstand hostile conditions upto 2800⁰C.
4. A circular disc of radius 0.2 meter is placed in a uniform magnetic field of induction
5. When two identical capacitors are in series, they have 3 μF capacitance

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