Answer:
B. 75,000nm
Explanation:
The wavelength of a wave can be calculated thus;
λ = v/f
Where;
λ = wavelength (m)
v = velocity of light = 3 × 10^8m/s
f = frequency (Hz)
According to this question, the EM wave has a frequency of 4THz i.e. 4 Terahertz = 4 × 10^12Hz
λ = 3 × 10^8 ÷ 4 × 10^12
λ = 3/4 × 10^(8-12)
λ = 0.75 × 10^-4
λ = 0.000075m
Based on the options given, this value is equivalent to 75,000nm, which means 75000 × 10^-9m.
