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Factors affectin cooling rate

Extracts from this document...

Introduction

Triple Physics has been asked to investigate the factors that affect the cooling rate of a liquid

Research:

There are three ways in which heat can be transferred:

Conduction:

Heat energy is conducted from the hot end to the cold end. It is transferred from atom to atom. At the hot end the atoms are vibrating a lot. The vibration is gradually passed along to the other atoms as they collide into each other. This happens in all substances, but in a metal something extra happens. A metal has many free-moving electrons. These free-electrons can travel through the metal, transferring the energy more quickly.

Convection:

The transfer of energy, by the movements of particles only in liquids and gases

Radiation:

Energy from the Sun reaches us after travelling through space at the speed of light. When this hits an object, some of it is taken in or absorbed. This makes the molecules vibrate more – and so the object hotter.

Objects take in and take and give out energy as radiation all the time. Different objects give out different amounts of radiation depending on their temperature and their surface.

Isaac Newton stated that the rate at which a warm object cools is approximately proportional to the temperature difference between the temperature of the warm object and the temperature of its surroundings. This is a typical cooling rate graph.

image00.png


Factors that affect the cooling rate of a liquid:

  1. Different sized beakers.
  2. Beakers made from different materials and colours.
  3. Conduction.
  4. Radiation.
  5. Evaporation.
  6. Infrared Waves.
  1. Different sized beakers.

Convection can only take place in gases and liquids. Convection cannot take place in a solid because particles have restrictive movement.

...read more.

Middle

Fair test:

Various factors affect the cooling rate of a liquid and these have been listed in my research. The one factor that I will be looking at is varying the surface area of the beaker. In order to carry out a sensible investigation to produce precise results, I will ensure that other factors that may contribute to the results are kept constant.

Start temperature: Ensure that the initial temperature reading of the water is always 70°C for all experiments. This is to make sure that there is no temperature variation in the start temperature. It will be taken into account that there will be a ±0.5% accuracy level of this reading.

Time: Ensure that the temperature readings are recorded as accurately as possible to sixty seconds for each experiment using a digital stopwatch.

Radiation: Heat Radiation travels through transparent material such as glass. Therefore wrap a layer of aluminium foil around the beaker.

Convection: Convection occurs when particles move from the hotter region to the cooler region. To ensure that no heat is lost due to this place an insulating material (wool) around the beaker.

Evaporation: When a liquid evaporates, faster particles escape from its surface to form a gas. However, unless the gas is removed, some of the particles will return to the liquid. Place an insulating material (wood) that fits into the top part of the beaker to reduce evaporation.

Room Temperature: While I carry out the experiment I will make sure that the room temperature is always the same using a thermometer with a ±0.5% accuracy level.

Apparatus:

Glass Thermometer: To measure the temperature of the liquid. (0-100°C)

5 beakers (Sizes: 400ml, 250ml, 150ml, 100ml, and 50ml):

...read more.

Conclusion

While doing the experiment, we might have measured the thermometer readings incorrectly which means that the results collected were inaccurate.

Another disadvantage of the experiment was that I did not control the external environment.

 If I were to do this experiment again, I could place the beakers in a water bath which would ensure that fluctuation of room temperature does not affect the experiment. Alongside this, I could use a digital thermometer which will produce more accurate readings and fewer human inaccuracies.

Inaccuracies also occurred when measuring out the 50ml of water because different members of the group measured the amount of water.

Changes:

In the new method I included a water bath to control the temperature of the external environment. I also included a digital thermometer to record the thermometer readings.

New method and diagram:

  1. Collect the following:

A Water Bath

5 different sized beakers

1 layer of Wool

Aluminium Foil

Digital Thermometer

100ml Measuring Cylinder

Stop Watch

Pipette

  1. Set up apparatus as shown below.

image02.png

  1. Boil the kettle
  2. Wrap aluminium foil around the beaker.
  3. Wrap wool around the beaker.
  4. Place a thermometer in the beaker.
  5. Once the kettle has boiled, carefully measure 50ml of the liquid into the measuring cylinder.
  6. Pour the water into the 400ml beaker.
  7. Carefully place the beaker into the water bath.

10.) Start the stopwatch.

11.) Record the thermometer readings every sixty seconds.

12.) Record readings in a suitable results table. There should be ten readings altogether.

13.) Repeat experiment for fair test.

14.) Repeat experiment varying surface area of beaker.

Inaccuracy of Equipment.

50ml measuring cylinder- to measure 50ml of water.

Thermometer - to measure the temperature of the water.

Measuring Cylinder

0.5/100 X 100=1% inaccuracy.

Thermometer

0.1/100 X 100=0.1% inaccuracy.

The measuring cylinder and thermometer caused the most inaccuracies, having a 0.1% inaccuracy.

...read more.

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