Question

Name the electromagnetic waves which are (i) also known as ‘heat waves’, (ii) used in LASIK eye surgery, (iii) used to destroy cancer cells. Also write their wavelength range.

Hint:

Match each use to infrared, ultraviolet or gamma rays, and quote the standard wavelength range of each.

Answer 1

Step 1: Understanding the Question:
The question asks us to match three uses to three parts of the electromagnetic spectrum. We must also give the wavelength range of each wave.

Step 2: Part (i) - heat waves:
Infrared waves are called heat waves. Hot bodies emit them, and water molecules in our skin absorb them, so we feel warmth.
Their wavelength range is about \(7 \times 10^{-7}\ \text{m}\) to \(10^{-3}\ \text{m}\) (700 nm to 1 mm).

Step 3: Part (ii) - LASIK eye surgery:
LASIK uses a laser beam of ultraviolet light to reshape the cornea. Ultraviolet photons carry enough energy to cut tissue cleanly without burning it.
Ultraviolet waves have wavelengths from about \(4 \times 10^{-7}\ \text{m}\) down to \(6 \times 10^{-10}\ \text{m}\) (400 nm to about 0.6 nm).

Step 4: Part (iii) - destroying cancer cells:
Gamma rays are used to destroy cancer cells. Their photons have very high energy, so they damage the cells in a tumour when directed at it.
Their wavelength range is about \(10^{-14}\ \text{m}\) to \(10^{-10}\ \text{m}\), that is, less than about 0.1 nm.

Final Answer:
(i) Infrared: \(7 \times 10^{-7}\ \text{m}\) to \(10^{-3}\ \text{m}\). (ii) Ultraviolet: \(4 \times 10^{-7}\ \text{m}\) to \(6 \times 10^{-10}\ \text{m}\). (iii) Gamma rays: \(10^{-14}\ \text{m}\) to \(10^{-10}\ \text{m}\).