Q01: Write down Pascal’s law. Mention one
of the uses of this law.
Pascal’s Law: When a fluid
completely fills a vessel and a pressure is applied to it at any part of the
surface, that pressure is transmitted equally throughout the whole of the
enclosed fluid.
pin = pout, Fin/Fout
= Ain/Aout
pin =
input pressure, pout = output pressure, Fin = input
effort,
Fout =
output load, Ain = area of intake piston, Aout = area of
outlet piston
1) Pascal’s law is very useful in
practical applications.
2) The constructions of hydraulic brakes
and hydraulic presses are based on Pascal’s law.
3) Hydraulic brakes are used in cars and
other road vehicles.
4) A hydraulic press is a very useful
machine. It is used for baling jute and for shaping steel and metal sheets. It
has numerous other uses, from the compression of soft metals into cups of
varying shapes to the pressing of automobile bodies.
2Q02: “Although Pascal’s law is not a
fundamental law, it is a very useful law for practical purposes.” Is this
statement correct? Discuss.
1) The statement is correct.
2) Pascal’s law is very useful in
practical applications.
3) The constructions of hydraulic brakes
and hydraulic presses are based on Pascal’s law.
4) Hydraulic brakes are used in cars and
other road vehicles.
5) A hydraulic press is a very useful
machine. It is used for baling jute and for shaping steel and metal sheets. It
has numerous other uses, from the compression of soft metals into cups of
varying shapes to the pressing of automobile bodies.
2Q03: Write down Archimedes’ principle.
2Q06: What will be the effect on the
mercury column if the glass tube used has (a) a smaller internal diameter (b) a
slightly bigger internal diameter?
1)
The height of mercury column depends only on the atmospheric pressure
outside the tube.
2)
It does not depend on cross-sectional area.
3)
So there will be no effect for both cases.
4)
The mercury column will remain at 76 cm.
2Q07: Will the mercury column be higher or
lower than 76 cm when the whole up of the barometer is taken to a high mountain
top?
1)
Less,
2)
because the pressure of the surrounding air is less than that at sea
level.
3)
This is because at greater heights air is thin.
2Q08: Why is mercury used in a barometer
rather than water?
1)
The
pressure exerted by the atmosphere is the same for water and mercury.
2)
pHg
= pW (Hg = mercury, w =
water)
3)
rHg g hHg
= rW g hW
4)
hw = (rHg hHg)/rw = 13.6 ´ 76 = 1033.6 cm = 10.336 m
5) Density of mercury is much larger
than that of water.
6) If mercury is used only 76 cm (about
1 m) of tube is needed.
7) If water is used 10.336 m (more than
10 m) of tube is needed.
8) Water barometer is much longer than
mercury barometer.
9) Thus, mercury is used in a barometer
rather than water.
2Q09(a): What is the effect on the vertical height of the mercury
column in a barometer of using a wider glass tube?
1)
The
vertical height of the mercury column in a barometer only depends on the
atmospheric pressure outside the tube.
2)
The
vertical height of the mercury is independent of the diameter or the
width of the tube.
3)
The
pressure in a liquid doesn’t depend on the container angle or width.
4)
Using
a wider glass tube will not change the height of the mercury column.
5)
The
height of the mercury column will remain at 760 mm.
2Q09(b): What is the effect on the vertical height of the mercury
column in a barometer of pushing the tube further into the bowl?
1)
The
vertical height of the mercury column in a barometer only depends on the
atmospheric pressure outside the tube.
2)
Pushing
the tube further into the bowl will not change the height of the mercury column
as long as the vertical height of the mercury column exceeds 760 mm.
2Q09(c): What is the effect on the vertical height of the mercury
column in a barometer of tilting the glass tube at an angle?
1)
The
vertical height of the mercury column in a barometer only depends on the
atmospheric pressure outside the tube.
2)
The
vertical height of the mercury does not depend on the tilt of the column as
long as the vertical height of the mercury column exceeds 760
mm.
2Q09(d): What is the effect on the vertical height of the mercury
column in a barometer of taking the barometer to the top of the mountain?
1)
The
vertical height of the mercury column in a barometer only depends on the
atmospheric pressure outside the tube.
2)
The
pressure at the top of the mountain is less than 760 mm Hg because the pressure
of the surrounding air is less than that at sea level.
3)
This
is because at greater heights air is thin.
4)
So
the height of the mercury column will be lower than 760 mm.
2Q14: Give the approximate value of atmospheric pressure at sea
level in (i) Pa
(ii) mm Hg (iii) atm?
(a) 105 Pa (b) 760 mm Hg (c) 1 atm
2Q14: Explain why the thickness of the dam increases downwards.
1)
The
thickness of the wall of the dam increases downwards because the deeper it is,
the greater the water pressure.
2)
A
thicker wall is required to withstand a greater pressure.
2Q15: A beaker containing water and placed on a pan is balanced by
the weight which is in the other pan of the balance. Explain what will happen
if a man immersed his finger in the water without touching the beaker.
1) If a man immersed his finger in the
water, there would be upward thrust on the finger.
2) Some water has to be displaced for
the finger according to the Archimedes’ principle.
3) This displaced water will show
unbalance of the balance.
2Q17: Steel will float in liquid (mercury)
but sink in water. So how does a steel ship manage to float in water?
R There is far more air in a ship than
steel, (because a ship is hollow and contains air), so the average density of
the ship is less than that of water.
2Q26: Why is it easier to float in the sea
than in a swimming pool?
1) The density of sea water is greater
than that of fresh water.
2) The upward thrust is directly
proportional to the density of the liquid. (Fup = rgV, Fup = upward thrust, r = density of liquid).
3) The upward thrust of sea water is
greater than that of the water in the swimming pool.
4) Thus, it is easier to float in the
sea than in a swimming pool.
