Question

A man covers his body with a blanket of thickness 4 mm. His temperature is 37°C and that of the atmosphere is 27°C. If the coefficient of thermal conductivity of wool is 1.2 × 10^-5 MKS units, heat lost by him per hour per square meter area is: 

Options

• 10.8 K cals

• 1080 K cals

• 1.08 K cals

• 108 K cals

Answer 1

108 K cals

Explanation - 

Using heat lost,

`(Δ"Q")/(Δ"t") = "KA" (Δ"T")/(Δx)  "or"  (Δ"Q")/(Δ"tA") = ("K"Δ"T")/(Δx)`

Given,

K = 1.2 × 10⁵ MKS, ΔT = 37°C - 27°C = 10°C

Δx = 4 mm = 4 × 10^-3 m² 

∴ `(Δ"Q")/(Δ"tA") "per hour" = (1.2 xx 10^(-5) xx 10)/(4 xx 10^-3) 60 xx 60 = 108` K cals