WAEC 2022 Physics · Question 28

The distance between the fixed points of a mercury-in-glass thermometer is 30 cm. Determine the temperature…

Question

The distance between the fixed points of a mercury-in-glass thermometer is 30 cm. Determine the temperature when the mercury level is 10.5 cm above the lower fixed point

A.28.6ºC
B.30.0 ºC
C.35.0 ºC
D.40.5 ºC

Answer: C. 35.0 ºC

Explanation written with AI and checked against the answer key

Analyze the question: A mercury-in-glass thermometer has its lower fixed point (ice point, 0°C) and upper fixed point (steam point, 100°C) separated by 30 cm. We need the temperature when the mercury is 10.5 cm above the lower fixed point. Concept: Mercury length varies linearly with temperature, so: θ = (l_θ − l₀) / (l₁₀₀ − l₀) × 100°C Here, l_θ − l₀ is the length of the mercury above the lower fixed point, and l₁₀₀ − l₀ is the full interval between the fixed points. Solution: θ = (10.5 / 30) × 100 θ = 0.35 × 100 θ = 35.0°C Answer: The temperature is 35.0°C, which is option C. Tip: In these thermometer questions, always set up the ratio (distance above the lower fixed point ÷ total fixed interval) × 100. Here, 10.5/30 simplifies quickly to 0.35, so you can do it fast in the exam. Check that your answer is reasonable: 10.5 cm is a bit more than a third of 30 cm, so a bit more than a third of 100°C, which is about 35°C.

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