The speed of light in a vacuum is 3 × 108 meters per second, Planck’s constant is 6.625 × 10-34 joules per second

The speed of light in a vacuum is 3 × 108 meters per second, Planck’s constant is 6.625 × 10-34 joules per second. It is necessary: to determine at what length of the electromagnetic wave the photon energy would be equal to 1 × 10-18 joule.

The photon energy E is determined by the formula:
E = hc / λ.
where h is Planck’s constant,
c is the speed of light,
λ is the length of the electromagnetic wave.
λ = hc / E = (6.625 * 10-34 J * s * 108 m / s) / (1 * 10-18 J) = 1.98 * 10-7 m.
Answer: At a wavelength λ = 1.98 * 10-7 m.