A student uses a red hosepipe to make a solar water heater - Edexcel - GCSE Physics - Question 2 - 2018 - Paper 1

As the sun rises, the temperature of the water in the hosepipe increases due to the heating effect of sunlight. Throughout the day, from sunrise to sunset, the temperature will continue to rise as the hosepipe absorbs solar energy. The peak temperature is likely to be reached around midday when sunlight is most intense. Toward sunset, the temperature will gradually decrease as the sunlight reduces, causing the water to cool down.

To calculate the efficiency of the heater, we can use the formula:

$\text{Efficiency} = \frac{\text{Energy absorbed}}{\text{Energy incident}} \times 100$

Given that:

• Energy absorbed = 15000 J - 6000 J = 9000 J.
• Energy incident = 15000 J.

Now substituting these values:

$\text{Efficiency} = \frac{9000}{15000} \times 100 = 60\%$

Thus, the efficiency of the heater is 60%.