MCQ Detailed View

Materials that are good absorbents of electromagnetic radiation—like black bodies or dark-colored surfaces—are also excellent radiators of energy. This principle is central to thermodynamics and heat transfer and is formally described by Kirchhoff’s Law of Thermal Radiation.

Key Concepts:

1. 
   

   Kirchhoff’s Law states that at thermal equilibrium, a body that absorbs electromagnetic radiation efficiently also emits (radiates) energy efficiently at the same wavelength.

   
   


2. 
   

   Black bodies are idealized perfect absorbers and perfect emitters. For example, a black-painted metal absorbs sunlight effectively and radiates heat efficiently.

   
   


3. 
   

   The radiation emitted depends on the temperature of the body and the nature of its surface. Dark, rough surfaces are generally better radiators than shiny, reflective ones.

   
   

Other options explained:

• 
  

  Conductors → Materials that allow electric current to flow easily; not necessarily related to radiation absorption.

  
  


• 
  

  Insulators → Materials that resist the flow of heat or electricity; poor emitters of radiation.

  
  


• 
  

  Semiconductors → Materials with intermediate electrical conductivity; their radiation properties depend on temperature and doping but are not generally correlated with absorption like black bodies.

  
  

Applications:

• 
  

  Solar panels use materials that absorb maximum sunlight (good absorbers) and convert it into electricity efficiently.

  
  


• 
  

  Thermal insulation design considers that surfaces that absorb heat can also radiate heat, which is critical for energy efficiency.

  
  


• 
  

  Astrophysics: Stars are nearly perfect black bodies, absorbing and radiating electromagnetic energy efficiently.

  
  

In summary, the correct answer is Radiators, because good absorbents of electromagnetic radiation naturally emit energy efficiently, following the fundamental principles of thermal physics