Question

If 10^–17 J of light energy is needed by the interior of human eye to see an object. The photons of green light (λ = 550nm) needed to see the object are.

• A. 27
• B. 28
• C. 29
• D. 30

Answer 1

Answer: (B)

28

Answer 2

Required energy = 10^–17 J = n × $\frac{hc}{\lambda}$

⇒ n× $\frac{6.625 \times 10^{- 34} \times 3 \times 10^{8}}{550 \times 10^{- 9}}$J = 10^–17 J ∴ n = 28