Density
3 marks · NormalDescribe how you would use a measuring cylinder to measure the volume of an irregular solid. Why is it important to ensure no air bubbles are trapped underneath the object?
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Must show: Describe measuring initial and final volumes, Subtract to find object’s volume, Explain error from trapped air bubbles
Common mistakes: Not mentioning air displacement; Not subtracting initial from final reading
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Marking points
M1 · 1 mark · Mentions measuring initial volume of water.
M2 · 1 mark · Mentions measuring final volume after adding object and subtracting to find volume of object.
B1 · 1 mark · Explains that air bubbles under the object would give an inaccurately high volume.
Worked solution
Measure the initial volume of water in the cylinder. Gently add the solid so it is completely submerged. Record the new volume. Subtract the initial volume from the final volume to get the object's volume.
Air bubbles would increase the volume reading, so it is important no air is trapped to get an accurate result.