Worksheet 18 1i7216

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PHYSICS GRADE 12 REVISION 2008 WORK SHEET 18 THERMAL PHYSICS (Specific heat capacity, Latent heat)

1. (a) Water has a “specific heat capacity of 4200JKg-1K-1”. Explain this statement.

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(b) An electric kettle has a heat capacity of 450JK-1 and an element whose power is

2.25KW. Ignoring the losses of energy to the surrounding, what is the rate of rise of temperature in Kmin-1 when the kettle contains 1.0Kg of water. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...........................................................................................................................................

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2. The following data refer to a dishwasher. Power of heating element 2.5KW Time to heat water 360s Mass of water used 3.0Kg Initial temperature of water 20 Final temperature of water 60 (a)Taking the S.H.C. of water to 4200JKg-1K-1, Calculate (i) The energy provided by the heating element ........................................................................................................................................... ........................................................................................................................................... ...........................................................................................................................................

(ii) The energy required to heat the water. ........................................................................................................................................... ........................................................................................................................................... ...........................................................................................................................................

(b) Give two reasons why your answers in part (a) differ from each other. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...........................................................................................................................................

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3. (a) Define the term ‘specific latent heat of vaporization’. ........................................................................................................................................... ........................................................................................................................................... ...........................................................................................................................................

(b) In an experiment to determine the specific heat of vaporization of a liquid, an electrical heater boils the liquid in a well insulated container. The resistance of the heater is 3.00Ω and the Potential difference across the heater is 8.00V. In a time of 500s, the mass of liquid decreases by 0.110Kg. Calculate (i) The energy transferred to the liquid. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... (ii) The specific latent heat of Vaporization of the liquid. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...........................................................................................................................................

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4. (a) Define the term specific latent heat of fusion and state briefly how this quantity can be measured for ice. Include a diagram. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...........................................................................................................................................

........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... (b) Ice is commonly used to cool drinks. If an ice cube, at a temperat re of 0 and of mass 0.0 5 is dropped into a ea er containin 0. 5 of ater ith an initial temperat re of calc late the final temperat re of the res ltin ater. ss me that no heat is exchanged with the surroundings. Specific heat capacity of water= 4.2KJ-1 K-1 Specific latent heat of ice= 3.4x105 JKg-1 ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...........................................................................................................................................

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5. (a) Describe how you would measure the specific latent heat of vaporization of water. (i) Draw the diagram of the experimental arrangement. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... (ii)

Explain how you could calculate the result.

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State the factors which lead to uncertainity in the result.

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(iv)

Describe the precautions you would take to make your result as accurate as possible.

........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... (b) The mass of liquid nitrogen in an open beaker is found to have decreased by 4.63g in 10minutes. If the S.L.H of vaporization of nitrogen at its boiling point is 1.99x10 5JKg-1, at what rate were the surroundings heating the beaker? Why is the heat capacity of the beaker irrelevant? ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...........................................................................................................................................

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