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Specific Heat Capacity and Latent Heat Questions - GCSE standard

Q15.

Bill and Ben design an experiment to find the specific latent heat of water.

They set up their equipment as shown in the diagram.

They have access to a power supply, a voltmeter, an ammeter, a stop-clock and a top-pan balance as well as the equipment shown in the diagram.

(a) Explain how Bill and Ben could use this equipment to determine an accurate value for the specific latent heat of water.

[6 marks]

This type of question is marked in two ways:

- the examiner looks for relevant points

- but also for a logical sequence...

It is not just a 'tick fest' - but a marker does look to see how many relevant points you have made, then considers how you have strung them together to put your answer into a 'level'

Level 3:

A detailed explanation of experimental procedure AND detailed discussion about accuracy

There must be a well-developed line of reasoning which is clear and logically structured.

All of the information presented is relevant and substantiated.

5 - 6 marks
Level 2:

EITHER

a detailed explanation of the experimental procedure

OR

a detailed discussion about accuracy

OR

a brief explanation of the experimental procedure and simple discussion about accuracy.

----------

There is a line of reasoning presented with some structure.

The information presented is relevant and supported by some evidence.

3 - 4 marks
Level 1:

EITHER

a brief explanation of the experimental procedure

OR

a simple comment about accuracy

-----------

There is an attempt at a logical structure with a line of reasoning.

The information is in the most part relevant.
1 - 2 marks
Level 0:

No response or no response worthy of credit.

0 marks

 

Examples of physics points that should be made in the response:

Apply knowledge and understanding of how to use the equipment to find specific latent heat of water.

For example:

- Measure the initial mass/weight of beaker

- Turn on the heater

- Start timing

- Use the voltmeter, ammeter and stopclock to calculate the energy supplied (E=VIt)

- Turn off the heater

- Stop timing

- Use a balance to measure the mass of the beaker and melted ice

- Subtract the original mass of the beaker to find the mass/weight of the melted ice

- Calculate specific latent heat by dividing energy by mass

Analyse information and ideas to develop experimental procedures and consider accuracy of the experiment.

For example:

- Make sure that the heater is always covered with ice

- Insulate/put lid on the funnel to reduce heat losses

- Make sure that the mass of water produced is sufficiently large to measure accurately – run the experiment for long enough

- Repeat the experiment to minimise (random) errors

(b) The students find that 250g of ice takes 95kJ of energy to change state.

Calculate the specific latent heat of fusion for water in J/kg.

If you cannot remember the equation look at the units you are given....

J/kg indicates that the latent heat is found by dividing energy by mass.

Specific latent heat of fusion = energy/mass

Energy must be in joules

95 kJ = 95,000J

Mass must be in kilograms

250g = 0.25 kg

Specific latent heat of fusion = 95,000/0.25

Specific latent heat of fusion = 380,000 J/kg

[5 marks]

(11 marks total)