Tiêu đề QUANTITY OF HEAT.pdf ✅

www.teachersofphysics.com 2020 TEACHERS OF PHYSICS www.teachersofphysics.com 9/3/2020 QUANTITY OF HEAT
www.teachersofphysics.com Copyright © 2020 HEAT CAPACITY 1. Define specific latent heat of fusion of a substance (1mk)  The quantity/amount of heat required to change a unit mass of a substance from solid to liquid at constant temperature. 2. Distinguish between heat capacity and specific heat capacity of a substance.  Heat capacity is the quantity/amount of heat required to raise the temperature of a given mass of a substance by one unit(1 K/10C) while specific heat capacity is the quantity/amount of heat required to raise the temperature of a unit mass(1 kg) of a substance by one unit(1 K/10C). 3. Give the property of water which makes it suitable for use as a coolant in machines (1mk)  Water has a high specific heat capacity hence absorbs a lot of heat per unit mass. 4. Equal masses of water and paraffin are heated for same length of time. The final temperature of paraffin was found to be greater than the final temperature of water. Explain the observation. (2mk)  Water has a higher heat capacity than kerosene hence more heat is required to raise its temperature by one unit compared to kerosene with a lower heat capacity. 5. A student states that when two bodies at different temperatures are brought into contact the resulting rise of temperature in one will be equal to the fall in temperature in the other. Give two reasons why this statement is wrong  The bodies may be of different materials hence different specific heat capacities.  The bodies may differ in size hence different heat capacities. 6. (i) Describe how you would attempt to measure the specific heat capacity of aluminium by method of mixtures. (3mk) Take a piece of aluminium, weigh it and record the mass, mA. Heat water in a beaker to its boiling point, θ1. Place the aluminium block in the boiling liquid for some minutes. Weigh a plastic beaker, mB (known heat capacity, CB). Take a known mass, mL of a liquid whose specific heat capacity is known, cL and pour in the plastic beaker and determine its initial temperature, θ0. Quickly transfer the block from the boiling water to the plastic beaker, stir and measure the final steady temperature of the mixture, θ2. Using the formula below calculate the specific heat capacity of aluminium. ( ) ( )
www.teachersofphysics.com Copyright © 2020 (ii) State one source of experimental error in this method. (1mk)  Errors when reading temperature  Some heat is lost to the surroundings (iii) Give one way you could take to reduce the magnitude of the error you have mentioned. (1mk)  Using a lagged calorimeter in place of a plastic beaker/Lagging the plastic beaker. 7. Briefly describe an experiment to determine the specific heat capacity of a liquid substance using the electrical method. (6mk) Take a well lagged calorimeter whose mass is known, mc. Measure the mass of the liquid, mL and pour it into the calorimeter(of known heat capacity, CC. Determine the initial temperature To and record. Place an immersion heater with a known power rating, P in the liquid. Switch the heater on and start a stop watch simultaneously. Stir the liquid while heating for about 5 minutes. Switch the heater off and stop the watch. Make the final temperature, Ti reading and time, t used for heating and record. Use the formula below to calculate the specific heat capacity of the liquid, cL. ( ) 8. A liquid at 80°C in a cup was allowed to cool for 20 minutes. State two factors that determine the final temperature. (2mk)  The surface area of the cup  The material making the cup  Temperature of the surroundings 9. Equal masses of water and ice at 00C are added separately into two identical beakers containing equal amount of water. State the reason why ice may cause a greater change of temperature. (1mk)  The ice has more heat to gain than water as it has to gain latent heat of fusion. 10. Figure below shows the temperature changes against quantity of heat supplied to one kilogram each of liquids A and B. Which of the two liquids has a high specific heat capacity? Give a reason.(2mk)  B. more heat is required to raise its temperature compared to A. A Tempereture (0C) Quantity of heat (J) B