Question

With respect to incident radiation, transmissivity varies with

• A. Time
• B. Temperature
• C. Surface area
• D. Wavelength

Hint:

Always associate transmissivity (and other radiation properties) with wavelength dependence, especially when analyzing spectral behaviors.

Answer 1

The Correct Option is D

Transmissivity ($\tau$) is defined as the fraction of incident radiation that passes through a material without being absorbed or reflected.
The value of transmissivity is not constant — it varies based on several factors, but the most fundamental of them is the wavelength of the incident radiation.
Radiative properties such as:
- Absorptivity ($\alpha$)
- Reflectivity ($\rho$)
- Transmissivity ($\tau$)
are all known to be wavelength-dependent because materials interact with different portions of the electromagnetic spectrum in different ways.
For instance:
- Glass is transparent to visible light (low wavelength), but
- It is opaque to infrared radiation (longer wavelength).
Incorrect options analysis:
Option 1: Time does not affect instantaneous transmissivity.
Option 2: Temperature affects emission, not transmissivity directly.
Option 3: Surface area affects quantity of energy, not fraction transmitted.
Therefore, transmissivity varies most significantly with wavelength.