Heat

CHAPTER 4: HEAT 1.(a) Diagram 9.1 and 9.2 shows two different situations that happen in our daily life. Diagram 9.1 shows a hand touching a hot kettle and Diagram 9.2 shows a hand holding an ice. Both are having different temperatures. The arrow in both diagrams indicates the direction of heat flow. (i) What is meant by temperature? [ 1 mark ]

2.(a) Figures 9.1 and 9.2 show two types of metal block of the same mass being heated using similar heaters for 10 minutes. Both metal blocks have the same initial temperatures of 30 oC. The specific heat capacity of copper is 387 J kg-1 oC -1 and 900 J kg-1 oC -1 for aluminium.

FIGURE 9.1 (ii) Using Diagram 9.1 and 9,2, compare the temperature of the objects, the effect of heat experienced by the hands and the direction of heat flow. Relate the direction of the heat flow to the difference in temperature between objects which are in thermal contact. [ 4 marks ] (b) Diagram 9.3 shows the phenomenon of sea breeze which occur during the day. Explain this phenomenon. [ 5 marks ]

(c) Diagram 9.4 shows a desk lamp placed on a desk used by a student. This type of lamp is not suitable to be used as a study lamp.

Diagram 9.4 Explain the modifications that can be made to improvise the desk lamp used by the student. Emphasize your explanation in the following aspects: (i) comfort the person who will use the lamp. (ii) to reduce the heat transfer for the desk lamp (iii) the design of the lamp desk (iv) safety features of the lamp (v) the energy efficiency of the lamp [ 10 marks ]

FIGURE 9.2 (i) “The specific heat capacity of copper is 387 J kg-1 oC-1”? What is meant by the statement above? [1 mark ] (ii) Using Figures 9.1 and 9.2, compare the increase in temperature and the specific heat capacity of the metals used. Relating the heat supplied, the heat absorbed and the specific heat capacity of the metals, deduce a relevant physics concept. [5 marks ] (iii) Name the physics principle that explains the above situation. [1 mark ] (b) A student standing near the beach could feel the cool breeze from the sea on a hot day. Explain how the cool breeze from the sea occurs. [3 marks ] (c) A parachutist intends to jump in the Artic region where the temperature ranges from – 72oC to 0oC. He needs to measure the daily temperature of the region where he will be doing his jump by using a liquid-in-glass thermometer. (i) State two suitable characteristics for the liquid used in the thermometer and explain your answer. [4 marks ] (ii) Explain three other important characteristics in building the thermometer. [6 marks ]

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Figure 9.1(a) Figure 9.2 (b) 3. (a) Figure 9.1(a) shows a boy pouring hot coffee into a cup. The hand of the boy is not scalded by the coffee droplets that are spattered from the kettle. Figure 9.1.(b) shows hot coffee spilling over and getting onto his hand and his hand gets scalded because of the heat capacity in it. i) What is meant by heat capacity? ( 1 mark ) ii) Using diagrams 9.1(a) and 9.1(b) , compare the situations , when the coffee droplets spatters on his hand and when the hot coffee from the kettle spills onto his hand. State the relationship between the heat capacity and the mass . ( 5 marks) (b) Explain why water is normally used as a cooling agent in a car engine. ( 4 marks) (c) An aluminium pan of mass 500 g is heated from 25° C to 105 º C . How much heat is absorbed by the pan ? ( The specific heat capacity of almunium is 910 Jkg −1 °C −1 ) (4 marks) (d) As a researcher, you wish to produce an ideal cooking pan which saves gas for the purpose of cooking. Using the appropriate physic concepts, suggest and explain the modifications required. (6 marks) 4.

Diagram 9.1 shows a student standing at the edge of a swimming pool with his right foot on a tiled floor while his left foot reaches into the water during the day time. His left foot feels colder than his right foot. On the other hand , if this action is repeated at night his left foot that is in the water with feel warmer than his right foot which is on the tiled floor, as shown in Diagram 1.2. DIAG

RAM 9.1 DIAGRAM 9.2

(a) ( i) What is meant by heat? [1 mark] (ii) Observe situation in diagram 9.1 and diagram 9.2. Compare the coldness of the floor tiles and the coldness of the water in the swimming pool. State the relationship between the heat content of the floor tiles and the water in the swimming pool in both situations. (b) Diagram 9.3 shows the car engine radiator. Explain why is water used in the cooling system of the car ?

(b) Using Diagram 9.1 and Diagram 9.2, compare the processes that take place in both situations and the type of heat needed for both processes to occur. Relate the processes with the type of heat needed to deduce a relevant physics concept. Name the physics concept involved. [5 marks]

6.(a) Diagram 6.1 and Diagram 6.2 show two mercury thermometers X and Y used to measure the boiling point of pre water. The two thermometers have equal bulb volume but different capillary length.

(c) (i) Your body sweats when you are

DIAGRAM 9.3 (a) In the car factory , En Ahmad realized that the engine always become overheated. Using a suitable physics concept, explain the required modification needed to design an engine that can operate longer and to prevent damage to the engine due to overheating. You should use your knowledge of heat to explain these suggestions, include the following aspects: (i) the design and structure of the radiator. (ii) the characteristic of cooling material. (ii) the suitable of boiling point. [10 marks] 5. Diagram 9.1 shows an ice cube melting when heat is absorbed from the surrounding. Diagram 9.2 shows a kettle of water boiling when heat is absorbed from the fire.

DIAGRAM 9.1

(d)

feeling hot. How does sweating helps to cool down your body? [ 2 marks ] (ii) Explain why a scald from steam is more serious than the one from boiling water? [ 2 marks ] Diagram 9.3 shows a simple solar water–heating system. Energy from the Sun falls on the solar panel. Water is pumped around the system so that a store of hot water is made available in the tank.

DIAGRAM 9.3 Using suitable physics concepts, explain the required modification needed in designing an efficient solar water-heating system. The modification should include the following aspects: (i) pipes design (ii) material used (iii) heat absorption

DIAGRAM 9.2

(a) What is meant by heat?

[10 marks]

[1 mark]

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(i)

Explain what is meant by the sensitivity of a measuring instrument? [1 mark] (ii) With reference to Diagram 6.1 and Diagram 6.2, compare the temperature measured by the two thermometers, the length of mercury threads, the diameter of the capillary tube and the sensitivity of the thermometers. Relate the length of the mercury threads and the temperature measured, make a deduction regarding the sensitivity of the thermometer and the diameter of the capillary tube of the thermometer. [5 marks] (b) Using your knowledge of heat capacities to explain phenomena sea breeze and land breeze. [4 marks] (c) A housewife decides to cook a meat. She is given two pots, a aluminium cooking pot and a clay pot. (i) Explain which pot is more suitable to be used if the housewife want to keep the food at a high temperature for a long time (ii) Give twp advantages of pot in (c)(i). [10 marks]

7.(a) Diagram 7.1 and Diagram 7.2 show a block of copper and a block of aluminium of equal mass heated by identical immersion heater of 50 W each.

8. Figure 9.1 and Figure 9.2 show two test tubes containing same mass of water and iron powder respectively. The water and the iron powder have different specific heat capacity, and they are heated at the same rate.

Specific heat capacity of copper = 387 Jkg-1 oC-1 Specific heat capacity of aluminium = 900 Jkg-1 oC-1 The temperature-time graphs for the two experiments are shown in Diagram 7.3 and Diagram 7.4 respectively.

Figure 9.1

Figure 9.2

Temperature of water = 35oC Temperature of iron powder = 85oC Specific heat Capacity of water = 4200 Jkg-1oC-1 capacity Specific Heat of iron powder = 460 Jkg-1oC-1

specific heat capacity ?

(i)

What is meant by specific heat capacity of a substance? [1 mark] (ii) With reference to Diagram 7.3 and Diagram 7.4, compare the mass, the change temperature and the energy absorbed by the objects. Relate the energies supplied to the objects, the masses of the objects and the change of temperature of the objects, deduce a relationship between the specific heat capacity and the change of temperature of the objects. [5 marks] (iii) Find the mass of copper used in the experiment. [4 marks] (b) You are given some materials to make a cooking pot. The materials are copper, wood and aluminium. Using the materials to explain how you are going to make the simple cooking pot. [10 marks]

(b) Based on Figure 9.1 and Figure 9.2, compare the temperature and specific heat capacity of water and iron powder. Relate the change in temperature and the specific heat capacity to come up with a conclusion of the physics concept involved. [5] (c) When a few drops of ether is dropped on a student’s hand, his hand felt cool. Explain how this happen . [4]

Figure 9.3 Figure 9.3 shows a food container used for keeping the food warm. Using the appropriate physics concepts, explain the modifications to a food container so that (i) it is able to maintain the temperature of food for a longer time (ii) it can be moved from one place to another [10]

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