Which type of electromagnetic waves are used in night vision devices and night vision apparatus?

Introduction / Context:
This question belongs to basic physics and applications of the electromagnetic spectrum. Night vision devices are widely used in military operations, surveillance, wildlife observation, and rescue work. They allow us to see in darkness by detecting radiation that is not visible to the human eye. Understanding which region of the spectrum is used in such devices is a common concept tested in school level physics and competitive exams.

Given Data / Assumptions:

• The question asks which type of waves are used in night vision apparatus.
• Options list radio waves, microwaves, infra red waves, ultraviolet waves, and None of the above.
• We assume the question refers to standard passive night vision and thermal imaging devices that detect heat signatures.

Concept / Approach:
All objects with a temperature above absolute zero emit electromagnetic radiation, a significant part of which for everyday temperatures falls in the infra red region. Night vision devices either amplify low levels of visible light or detect infra red radiation emitted by warm objects. Thermal imagers in particular are based on infra red detection, converting these waves into electronic signals and then into a visible image. Radio waves and microwaves are used for communication and radar, while ultraviolet waves are higher energy waves that do not form the basis of common night vision goggles.

Step-by-Step Solution:
Step 1: Recall that the human eye responds to visible light only, roughly from 400 nm to 700 nm in wavelength. Step 2: Understand that in darkness, there is very little visible light, but warm bodies (humans, animals, vehicles) still emit infra red radiation. Step 3: Night vision and thermal imaging devices are designed with sensors that detect infra red waves instead of or in addition to visible light. Step 4: Radio waves and microwaves are used for wireless communication, broadcasting, and radar, not directly for forming images of warm bodies in standard night vision goggles. Step 5: Ultraviolet radiation is higher energy and is typically blocked by the atmosphere and most glasses, so it is not used in conventional night vision apparatus. Therefore, infra red waves are the correct answer.

Verification / Alternative check:
A quick way to verify is to think about the term thermal imaging. Thermal implies heat, and heat radiation in physics is strongly associated with infra red emission. Many devices are specifically named infra red cameras or IR goggles. In contrast, there is no common phrase like radio wave night vision or microwave night goggles in basic physics textbooks. This terminology and the connection to body heat confirm that infra red waves are the correct type.

Why Other Options Are Wrong:
Radio waves: Used for broadcasting and communication, they have wavelengths much longer than needed for thermal imaging. Microwaves: Used in microwave ovens, radar, and communication, not in standard night vision goggles. Ultraviolet waves: High energy radiation used in sterilisation and special lamps, not for ordinary night vision. None of the above: Incorrect because infra red waves, listed in the options, are indeed used in night vision apparatus.

Common Pitfalls:
Students may confuse radar based detection, which uses microwaves or radio waves, with optical night vision, leading to a wrong choice. Another mistake is guessing ultraviolet because it is also invisible, without considering that the devices are detecting heat, not high energy radiation. To avoid such errors, always link night vision and thermal imaging with infra red, the region most strongly associated with heat radiation in physics.

Final Answer:
Night vision devices commonly use infra red waves to detect objects in darkness.