Question

4. If we use 12 mm thick special glass in the windows
of a room, instead of 3 mm thick ordinary glass,
and the temperature inside the room is higher than
that outside by 10°C , then how much heat per
hour will be prevented from going out? The total
area of glass is 5 mº and the thermal conductivity is
2 x 104 kcal s-1m-1°c-1. Ans. 9000 kcal.​

Answer 1

The heat per  hour is 9000 k cal.

Explanation:

Given that,

Thickness of special glass = 12 mm

Ordinary glass = 3 mm

Change in temperature = 10°C

Area = 5 m²

We need to calculate the energy per hour

Using formula of energy

$\dfrac{Q}{t}=\dfrac{kA\Delta T}{d}-\dfrac{kA\Delta T}{d}$

Put the value into the formula

$\dfrac{Q}{t}=KA\Delta T(\dfrac{1}{12}-\dfrac{1}{3})$

$\dfrac{Q}{t}=2\times10^{-4}\times5\times10\times\dfrac{1}{4\times10^{-3}}\times3600$

$\dfrac{Q}{t}=9000\ kcal$

Hence, The heat per  hour is 9000 k cal.

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Topic : heat per hour

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