Answer the following
(a) Name the em waves which are used for the treatment of certain forms of cancer. Write their frequency range.
(b) Welders wear special glass goggles while working. Why? Explain
(c) Why are infrared waves often called heat waves? Give their one application.

Hint:Electromagnetic waves show dual nature. It can act as a wave as well as a particle. Its velocity, frequency and wavelength represent its wave nature. The electromagnetic spectrum consists of various types of electromagnetic radiations which differ from one another in wavelength or frequency. The electromagnetic spectrum includes radio waves, microwaves, infrared lights, ultraviolet, X-rays, gamma rays etc. If the wavelength of radiation increases its frequency is going to decrease.

Complete step by step answer:
(i) According to the em wave’s spectrum, Gamma rays are used for cancer treatment. Its frequency range is $3\; \times \;{10^{19}}\;{\text{Hz to 5}} \times {\rm{1}}{{\rm{0}}^{24}}\;{\rm{Hz}}$.

(ii) Welders wear special glass goggles while working because the rays come in the form of UV –radiation. UV radiation often carries the unfortunate circumstance of containing too much energy. It may also cause skin cancer and other eye problems.

(iii)  Heat waves are those waves which carry heat along with them. The wavelength of infrared waves is sufficient to set atoms and molecules into vibrational motion. Hence whenever an object is hit by infrared waves, produces heat due to the vibrations of atoms. That is the reason why infrared waves are called heat waves. Infrared waves are used in burglar alarms, security lights etc.

Note:Electromagnetic radiation like light consists of photons which are discrete packets of energy. These particles when falls onto a surface exerts a pressure on the surface called the radiation pressure. The wavelength of infrared radiation is greater than that of visible light radiation.