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Example.1

Example.1. The stem of a mercury-in-glass thermometer is placed against a ruler. It has readings of 1.5 cm and 21.5 cm on the ruler at temperatures of 0 o C and 100 o C respectively. Find the increase in length of the mercury thread per o C.

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Example.1

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  1. Example.1 • The stem of a mercury-in-glass thermometer is placed against a ruler. It has readings of 1.5 cm and 21.5 cm on the ruler at temperatures of 0 oC and 100 oC respectively. • Find the increase in length of the mercury thread per oC. • What is the distance between the readings at 0 oC and 75 oC ? • What is the reading on the ruler at 75 oC?

  2. Example.2 • A drill is used to bore a small hole in a block of iron of mass 75g. The temperature of the block increases from 30 oC to 52 oC after drilling. The specific heat capacity of iron is 470 Jkg-1oC-1. • How much energy is used to heat the block? • If the drilling takes 10s and the power of the drill is 200 W, find the percentage loss of energy during heating

  3. Example.3 • In a bathroom, there is one hot water tap and one cold water tap. They deliver water at 0.5 kg per second at 65 oC and 0.2 kg per second at 25 oC, respectively. Both taps are turned on for 2 min. • What is the mass of water in the bath? • What is the temperature of the water in the bath? • If a final temperature of 45 oC is wanted, which tap should be turned on and for how much longer?

  4. Example.4 • In a experiment, 0.5 kg of oil in a polystyrene cup was heated using a 200 W immersion heater for 10 min. The temperature of the oil was recorded at regular intervals and plotted against time as shown. • What is the room temperature? • What is the slope of the temperature-time graph? What does this represent? • Find the equation of the graph and hence find the specific heat capacity of the oil. • Explain briefly why a polystyrene cup is used as the container.

  5. T or F? • Heat is a form of energy stored in a body.

  6. Ans • Heat is not a form of energy that can be stored in a body. • Heat is the energy transferred in the process of heating. • The energy stored in a body is called the internal energy.

  7. T or F? • Heat flows from an object which contains more internal energy to one which contains less.

  8. Ans • Heat flows from a hotter object to a colder object.

  9. T or F? • Objects that feel colder than others must have a lower temperature.

  10. Ans • Objects that feel colder than others may not have a lower temperature. • For example, a metal block feels colder than a piece of wood at the same temperature. • It is because heat is a transferred away from your hand more rapidly to the metal than the piece of wood.

  11. T or F? • Clothes provide us heat and keep us warm.

  12. Ans • Clothes keep us warm by slowing down the heat flow away from our bodies. They are not sources of heat.

  13. T or F? • Good insulators can stop the process of heat transfer.

  14. Ans • Good insulators cannot stop the process of heat transfer, they can only slow down the process.

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