Pressure and depth
3 marks · NormalA student makes a homemade water barometer. The atmospheric pressure supports a column of water 10.0 m high. The density of water is 1000 kg/m³ and g = 10 N/kg.
Calculate the pressure the atmosphere is applying to the water.
State one reason why mercury is often used in barometers instead of water.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) 100,000 Pa · must show substitution of correct values, calculation
(b) Mercury is denser than water so the barometer can be much shorter · must show density, column height
Also accept: Mercury is denser so shorter columns needed
Common mistakes: Forgetting density difference
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Correct substitution into p = hρg
A1 (a) · 1 mark · Correct value for pressure (100,000 Pa) (follow-through)
B1 (b) · 1 mark · Valid reason given (e.g. mercury is denser)
Worked solution
a)
b) Mercury is denser than water, so the column required is much shorter and the barometer is easier to handle.