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JAMB Physics 1983 Question 42

Question 42

Thermal Expansion

Which of the following statements clearly describe the behaviour of the fire alarm shown in Fig. 8 below given that the linear expansivities of copper and steel are 2.0 × 10−5/°C and 1.2 × 10−5/°C respectively? I. The bimetallic strip will not be able to close the circuit when there is fire II. The bimetallic strip will close the circuit when there is fire III. If the copper and steel are interchanged, the circuit will close when there is fire.

Diagram for this question
  1. A.I only
  2. B.II only
  3. C.III only
  4. D.I and III
  5. E.II and III.
Show the answer and explanation

Answer: D (I and III)

Explanation

Copper expands more, so when heated the strip bends towards the steel side, away from the contact above it; the circuit stays open (I). With the metals swapped it bends up to the contact and rings the bell (III).