Problem 2188 - JEE Physics

Question

Bolometer is used to detect (A) infrared rays (B) ultraviolet rays (C) x rays (D) \(\gamma\) rays

Step-by-Step Solution

Answer

A Bolometer is a sensitive instrument used to measure the intensity of radiation by the amount of heat it produces when it is absorbed by a material. Bolometers are particularly sensitive to long-wavelength radiation, specifically infrared radiation. Thus, the correct answer is (A) infrared rays.

Step 1: Understand what a Bolometer is

A Bolometer is a sensitive instrument used to measure the intensity of radiation by the amount of heat it produces when it is absorbed by a material. It typically consists of an absorptive element connected to a thermal reservoir through a thermal link. The temperature change of the absorptive element is then measured, which is proportional to the power of the incident radiation.

Step 2: Determine the type of radiation detected by a Bolometer

Bolometers are particularly sensitive to long-wavelength radiation, specifically infrared radiation. This is because the longer wavelengths are more readily absorbed by the material in the Bolometer, leading to a greater temperature change and thus a stronger signal. Additionally, Bolometers have been widely used in astronomical and earth remote sensing applications for detecting infrared radiation. Therefore, the correct answer is: (A) infrared rays

Key Concepts

Infrared Radiation Detection

A bolometer is a valuable tool when it comes to detecting infrared radiation. Infrared rays are electromagnetic waves that have a longer wavelength than visible light but shorter than microwaves. They are commonly associated with heat. Many objects naturally emit infrared radiation, primarily due to their temperature.

Bolometers are particularly effective in picking up infrared radiation because of their sensitivity to temperature changes caused by absorbed heat. This makes them indispensable in various applications, including

• astronomy, where they help detect celestial bodies emitting infrared radiation,
• earth remote sensing, which involves monitoring environmental and weather conditions from space,
• security systems to detect heat signatures, and
• industrial systems where thermography is needed.

These applications rely on the capability of a bolometer to convert absorbed infrared radiation into measurable temperature changes, allowing for precise readings and potential detailed insights into the observed objects or areas.

Thermal Absorptive Element

At the heart of a bolometer lies the thermal absorptive element, which plays a crucial role in its functioning. This element is a material designed to absorb incoming radiation effectively. When infrared radiation strikes this component, it results in a temperature rise due to the absorption of energy.

The responsive nature of the absorptive element is essential. Typically, materials with a high heat capacity and thermal conductivity are used. This ensures that the change in temperature is both significant and rapid, leading to an accurate measure of the radiation's intensity. The energy absorbed causes a temperature difference from a reference state, often referred to as the thermal reservoir or linked thermal sink.

Understanding this concept is important because the sensitivity and accuracy of a bolometer largely depend on the efficiency of its thermal absorptive element. Selecting the right material can greatly improve its performance in detecting weak or faint infrared signals.

Radiation Intensity Measurement

Radiation intensity measurement is the key outcome of using a bolometer, which essentially involves determining how much energy is being received by the device. To understand this, consider that the absorbed infrared radiation causes a temperature increase in the absorptive element. This change is directly correlated with the power or intensity of the incident infrared radiation.

The measurement process involves detecting the temperature change and converting this data into a power value. Engineers and scientists utilize this capability to gain insights into the properties of the source of the radiation. For example, by measuring the radiation intensity from a star or a remote planetary surface, they can analyze its composition, temperature, and movements.

The bolometer's ability to provide precise and reliable intensity measurements is vital in fields such as astrophysics and climatology, where understanding the characteristics of different radiation sources helps in developing comprehensive scientific theories or environmental models.