The inside of a vacuum flak is usually coated with silver to reduce heat loss by

Assessment: WAEC SSCE - Physics - 1998 (Objective) Subject: Physics

Question 1 Report

The inside of a vacuum flak is usually coated with silver to reduce heat loss by
Answer Details
The correct answer is **radiation**. Heat can be transferred through vacuum by radiation, which is the emission of electromagnetic waves from a body due to its temperature. A vacuum flask consists of two walls of glass with a vacuum in between them, and this vacuum is a poor conductor of heat, which reduces heat loss by conduction and convection. However, the inner wall of a vacuum flask can still lose heat by radiation. Hence, to reduce heat loss by radiation, the inside of a vacuum flask is usually coated with a reflective surface, typically silver, which reflects heat back into the flask, keeping the contents warmer for longer.
Read lesson note on Heat Transfer (JAMB)
Read lesson note on Heat Energy (WAEC)
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