If you grip the bulb of a thermometer gently in your fingers, the reading rises to a new value. The reading will be different depending on whether you cover the bulb entirely or only partially with your fingers. A laboratory thermometer can be used to measure the increase in temperature.

a. Suggest a value for the uncertainty in such a reading. (You may need to look at some different thermometers.)

b. Describe how you would test whether the temperature rise is proportional to the area of the bulb covered by your fingers You can take the surface area of the bulb to be 1 cm² and when you cover half of the bulb the area covered is 0.5 cm². The exact value of the surface area is not important; just the ratio is important.

c. Suggest difficulties with this experiment, and how it might be improved. One problem with a thermometer is that it takes time for the reading to rise. What can you do about this?

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Problem Improvement "Taking readings for just two masses was not enough.' 'Use more than two masses and plot a graph of the force against the mass.' 'It was difficult to zero the newton-meter used 'Use a force sensor and computer.' horizontally. 'Use a pulley and string to connect a tray to the block. Then tip sand onto a tray until the block starts to move. The weight of the sand and tray is then the force.' 'Use heavier masses on top of the block.' "The reading of F was very low on the scale and gave a large percentage uncertainty.' "The block starts to move Video the experiment and play back frame by frame to see the largest force.' suddenly and it is difficult to take the reading as this happens.' 'Use a force sensor and computer.' 'Different parts of the board are rougher than others.' 'Mark round the block with a pencil at the start and put it back in the same place each time.'