A warehouse wall of area originally has of insulation with thermal conductivity

PHYSICS · Single correct · A Level · Physics · Further mechanics and thermal physics · Further mechanics and thermal physics

Problem

A warehouse wall of area

200\,\text{m}^2

originally has

2\,\text{cm}

of insulation with thermal conductivity

0.08\,\text{W\,m}^{-1}\text{K}^{-1}

. It is replaced by

5\,\text{cm}

of insulation whose thermal conductivity is

0.04\,\text{W\,m}^{-1}\text{K}^{-1}

. The indoor–outdoor temperature difference is maintained at

15\,\text{K}

for

180

days each year. If electricity costs Rs

6

per kWh, the annual saving in heating cost due to the new insulation is closest to (a) Rs

1.6\times10^{5}

(b) Rs

7.5\times10^{5}

2.5\times10^{5}

(d) Rs

4.1\times10^{4}