Question

Name a medium which is a good insulator of heat.

• A. Still (or trapped) air
• B. Oil
• C. Steam
• D. solid copper
  

Answer 1

The correct option is A Still (or trapped) air

Trapped (still) air is good insulator.

Thermal conductivity of air is small as compared to solid and liquid. Eg- glass conducts 30 times more power per unit distance per unit temperature than air.

The less dense the material, the less thermal conductivity. And gas (air) is least dense than solid and liquid.