Question

What are infrared waves ? Why are these waves referred to as ‘heat waves’ ? Give any two uses of these waves.

Hint:

Remember: Visible Red \(\rightarrow\) Infrared \(\rightarrow\) Microwaves Infrared radiations are strongly absorbed by matter and therefore produce heating effects, which is why they are called heat waves.

Answer 1

Concept: Infrared radiations are electromagnetic waves lying beyond the red end of the visible spectrum. These waves were discovered by William Herschel and form an important part of the electromagnetic spectrum. Electromagnetic waves are classified according to their wavelength and frequency. Infrared radiations occupy the region between visible light and microwaves.

Step 1: Define infrared waves. Infrared waves are electromagnetic radiations having wavelengths greater than those of visible red light and smaller than those of microwaves. Their wavelength range is approximately \[ 7\times10^{-7}\,\text{m} \] to \[ 10^{-3}\,\text{m}. \] Thus, infrared radiations lie immediately beyond the red region of the visible spectrum.

Step 2: Explain why infrared waves are called heat waves. Every hot object continuously emits infrared radiations. When infrared radiations fall on a substance, they are readily absorbed by the molecules of the substance. The absorbed energy increases the vibrational and rotational motion of molecules, resulting in an increase in temperature. Thus, infrared radiations produce a strong heating effect. Since these radiations are mainly responsible for the heating sensation received from the Sun, heaters and other hot bodies, they are commonly known as \[ \boxed{\text{Heat Waves}}. \]

Step 3: Discuss the properties responsible for their heating effect. Infrared radiations possess lower frequencies than visible light but carry sufficient energy to excite molecular vibrations. Most materials absorb infrared radiations efficiently. As a result, the absorbed radiant energy is converted into thermal energy. This is the reason why infrared radiations are extensively used wherever controlled heating is required.

Step 4: State any two uses of infrared waves. Use 1: Infrared Photography Infrared photography is used for photographing objects in fog, haze, smoke and darkness where visible light photography becomes difficult. Use 2: Remote Control Devices Infrared radiations are used in television remotes, air-conditioner remotes and various wireless control systems for transmission of signals. Other important applications include:
• Physiotherapy and heat treatment.
• Night vision devices.
• Thermal imaging cameras.
• Drying of paints and agricultural products.
• Satellite and astronomical observations. Final Answer: Infrared waves are electromagnetic waves having wavelengths longer than visible red light and shorter than microwaves. They are called heat waves because they produce a strong heating effect when absorbed by matter. Any two uses are:
• Infrared photography.
• Remote control devices.