JEE Main 2022 · 26 June · evening · Single correct · +4 / −1
Which is the correct ascending order of wavelengths?
- (a) λ visible < λ X-ray < λ gamma-ray < λ microwave
- (b) λ gamma-ray < λ X-ray < λ visible < λ microwave
- (c) λ X-ray < λ gamma-ray < λ visible < λ microwave
- (d) λ microwave < λ visible < λ gamma-ray < λ X-ray
Answer and solution
Answer (b) λ gamma-ray < λ X-ray < λ visible < λ microwave
Solution
Physics sir · 3 steps
Line them up by photon energy: the most energetic waves are the shortest, so gamma rays come first.
- Energy and wavelength. A photon's energy is E = hc/λ. Higher energy means shorter wavelength, so ascending wavelength is the same as descending energy.
Radiation Typical wavelength Place in ascending order Gamma rays below about 10⁻¹¹ m 1st (shortest) X-rays about 10⁻¹¹ to 10⁻⁸ m 2nd Visible light about 400 to 700 nm 3rd Microwaves about 1 mm to 0.1 m 4th (longest) - Gamma versus X-ray. Gamma rays come from changes inside the nucleus, which release far more energy than the electron transitions that give X-rays. So gamma rays have the shorter wavelength.
- So. The ascending order is λ_(gamma) < λ_(X-ray) < λ_(visible) < λ_(microwave), which is option (b).
The idea to keep. Learn the spectrum once in order of wavelength: gamma, X-ray, UV, visible, IR, microwave, radio. Energy and frequency run the other way, from gamma down to radio.
Answer from the NTA final answer key. Solution by PrepWiser.