The U-value of the material in a double-glazed window in a house is 2.8 W m⁻² K⁻¹ - Leaving Cert Physics - Question d - 2014

Using the formula for heat loss,

$$Q = U imes A imes ∆T$$

where:

• Q is the heat loss (in watts),
• U is the U-value (2.8 W m⁻² K⁻¹),
• A is the area of the window (3.0 m²),
• ∆T is the temperature difference (9 °C).

Plugging in the values, we get:

$$Q = 2.8 imes 3.0 imes 9 = 75.6 ext{ W}$$

To find the total energy lost in one hour, we convert the time to seconds:

$$1 ext{ hour} = 3600 ext{ seconds}$$

Now, multiply the power loss by the time:

$$E = Q imes t = 75.6 ext{ W} imes 3600 ext{ s} = 271,200 ext{ J}$$

Therefore, the energy lost through the window in one hour is 271,200 J.