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Calculate the energy in joule corresponding to light of wavelength 485 nm: (Planck’s constant h = 6.63 × 10⁻³⁴ Js; speed of light c = 3 × 10⁸ ms⁻¹)

1. 6.67 × 10¹⁵
2. 6.67 × 10¹¹
3. 4.42 × 10⁻¹⁵
4. 4.42 × 10⁻¹⁸

Correct answer: 4.42 × 10⁻¹⁸

Solution

The energy of light is calculated using the formula E = hc/λ. Substituting h = 6.63 × 10⁻³⁴ Js, c = 3 × 10⁸ m/s, and λ = 485 nm = 485 × 10⁻⁹ m, we get E = (6.63 × 10⁻³⁴ × 3 × 10⁸) / (485 × 10⁻⁹) = 4.42 × 10⁻¹⁸ J.

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