Planning A Fair Investigation

D. Crowley, 2008

Planning A Fair Investigation

• To plan a fair investigation and make predictions

Wednesday, April 19, 2023

Thermometers

• Complete the thermometers worksheet

Questions• Different thermometers and sensors measure different temperature ranges.

If you need to measure the temperature, you need to choose the right thermometer or sensor for the job.

1. Many school science departments used to use mercury in glass thermometers, but now use alcohol in glass instead. Write down two reasons why you think they changed

2. An expedition to the Antarctic needs to choose a thermometer to take with them. Which kind of thermometer would you recommend? Explain your answer

3. If you feel ill, your parents or a doctor may take your temperature. Which kind of thermometer do you think your parents would use? Explain your answer

4. Liquid crystals can be made into flexible strips that can be held against someone’s forehead. Why do you think these thermometers are often used to take the temperature of young babies

5. Which kind of sensor could be used to control the temperature inside a fridge? Explain your answer

Answers1. Mercury is poisonous, so is very dangerous if a thermometer is

broken. Alcohol in glass thermometers is not poisonous, and are much cheaper than mercury thermometers

2. Alcohol in glass, because they measure colder temperatures than mercury in glass thermometers

3. Alcohol in glass, because it is cheap

4. It is difficult in keeping a normal thermometer under a baby’s arm or in their mouth

5. Thermistors are used inside fridges as these can be used as part of an electrical circuit to regulate the fridge temperature. A thermocouple may also be used as it can produce an electrical signal as an output

Investigation• Your task is to read, and complete the investigation – when you

have completed the diagram, instruction sheet and predictions undertake your experiment

• Once you have completed the experiment write down your results, and identify your findings – think about this experiment in terms of energy transfer: why does the water cool down when it is no longer heated, and where has this energy gone?

Investigation• Heating apparatus with beaker, thermometer, Bunsen burner, tripod,

stop watch, measuring cylinder, gauze, heat proof mat

Instructions:• Measure out an appropriate amount of water, e.g. 50cm3 and set up

your equipment (Bunsen burner on heat proof mat, underneath tripod with gauze on it)

• Add the water to the beaker, and begin heating (on full flame). Time how long the water takes to boil and record your result

• Now change the amount of water and repeat (measuring appropriate amounts) – you should do 5x different quantities of water

*If time permits, repeat this experiment (3x per quantity)

Investigation• Adam & Roger should measure the time taken for the water to boil

• A stop watch should be used to measure the time taken for the water to boil

• Adam and Roger should keep the intensity of the flame; the point of boiling (always 100oC); distance from the flame; beaker used; type of water (i.e. always tap, not tap, salty, distilled etc…) etc…

• Adam and Roger should find as the amount of water increases the time taken to boil also increases

• Water boils when virtually all the particles have enough energy to overcome the forces of attraction and escape. If you increase the quantity of water, you will need to heat more particles - so it will take longer to heat them all to their boiling point

Energy Transfer• Where is the energy transfer when water is heated?

• Initially the energy is chemical (within the fuel for the Bunsen burner) – this changes to heat which boils our water (the particles are heated, meaning they have more kinetic energy, moving around a great deal)

• When no more heat is applied, the water begins to cool down. This heat energy has not been destroyed, instead it has been transferred to the kinetic movement of the water particles which are moving around the beaker / boiling off

• There is also a great deal of heat transferred from the water to the surroundings (through conduction, convection and radiation)…