Calculate the wavelength of light travelling with a speed of 3 × 108$ms^{-1}$ and a frequency of 6.2 × 1014Hz.

Analyze the question: We're given the speed (v) and frequency (f) of light and asked for the wavelength (λ). Note that the speed is 3 × 10⁸ m/s and the frequency is 6.2 × 10¹⁴ Hz.

Concept: For any wave, the wave equation links speed, frequency and wavelength:

v = fλ, so λ = v / f

Solution:

λ = (3 × 10⁸) / (6.2 × 10¹⁴)

• Divide the numbers: 3 ÷ 6.2 ≈ 0.4839
• Subtract the powers of 10: 10⁸ ÷ 10¹⁴ = 10⁻⁶

λ = 0.4839 × 10⁻⁶ m

Convert to standard form: λ = 4.839 × 10⁻⁷ m ≈ 4.8 × 10⁻⁷ m

This is about 480 nm, which falls in the visible light range (blue-green), so the answer makes physical sense.

Answer: Option B, 4.8 × 10⁻⁷ m.

Exam tip: After dividing, always check that your coefficient is between 1 and 10. Here 0.48 × 10⁻⁶ must be rewritten as 4.8 × 10⁻⁷. Many students pick the wrong option (C) by forgetting this step. Also, visible light wavelengths are always roughly 4 × 10⁻⁷ m to 7 × 10⁻⁷ m, so you can quickly eliminate the other options.