1. SCIENCE EXPRESSION WORKBOOK ANSWERS
CHAPTER 7 – THERMAL PROPERTIES AND THERMOSTAT
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1. D 2. B 3. D 4. B 5. C
6. The three effects of heat are : change of state, change of temperature, thermal
expansion and contraction.
7. a) melting b) boiling/ evaporation c) condensation d) freezing/solidifying
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8. A hot rivet is inserted through the holes in between two metal plates. One end of the
rivet is hammered to form a new rivet head. When the rivet cools, it contracts and pulls
the metal plates together tightly.
9. (a) A bimetallic strip is made up of different metals welded or riveted together. At
room temperature, the strip is flat. As the surrounding heats up, the bimetallic strip in a
thermostat bends because one metal expands more than the other. This bending breaks
the electrical contact and switches off the current flowing to the electrical appliance. As
the surrounding cools down, the bimetallic strip contracts and straightens back to its
original position. The contacts touch and the electricity again flows through the electrical
appliance.
(b) Electric iron, rice cooker, electric oven, electric kettle
10. (a) When the iron becomes hot, the bimetallic strip expands due to uneven expansion
of the different metal strips. The bimetallic strip bends away from the contact point. This
causes the circuit to break.
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10. (b) The temperature knob should be adjusted to move the screw towards the contact
points for hot ironing. This adjustment allows the bimetallic strip to expand more at
higher temperatures before it bends away from the contact point causing the circuit to
break. As a result, the average temperature of the electric iron is increased for hot ironing.
11. When there is a fire, the bimetallic strip is heated. The bimetallic strip curves to close
up the contact point due to uneven expansion of the two metals. The electrical circuit is
closed and an electrical current flows through the electric bell. The electric bell rings to
sound the fire alarm.