Page 89 - Physics

Density and relative density

A density bottle has a precisely 6. The difference between m and m gives
measured volume, usually 25 ml, 2 1
50 ml, or 100 ml and a tight-fi tting the mass of the water added to the bottle.
(
stopper with a small hole to allow Mass of water is m − m ).
1
2
excess liquid to escape. It is mostly 7. Since the density of water is 1 g/cm , the
3
used in studying and analysing the volume added to the bottle is given in cm ,
3
relative densities of two immiscible which is numerically equal to the mass of
liquids. Figure 4.5 shows parts of a
density bottle. the water in grammes. mass of water m ( )
volume of water V ( ) = w
w density of water ρ ( )
Thin bore Glass stopper w
m m
w
Thus, V = V = w
w ρ w 1 g/cm 3
w
50 ml = (m −m ) g
2
1
Liquid 1 g/cm 3
3
= (m −m ) cm .
2
1
Figure 4.5: Density bottle
3
Therefore, the volume of water is in cm .
The following steps are to be
followed when using a density 8. Since the only materials in the bottle are
bottle to measure the density of water and sand, the sum of their volumes
insoluble granules such as sand. must be equal to the volume of the bottle.
1. Measure the mass of the empty That is,
density bottle with its stopper; volume of bottle = volume of sand + volume of water.
record as m . volume of bottle = volume of sand + volume of water.
0
2. Remove the stopper, add a
small amount of sand to the Then,
bottle and replace the stopper. volume of sand = volume of bottle − volume of water
volume of sand = volume of bottle − volume of water
Measure the mass of the bottle
containing sand and its stopper; V = V − V
record this mass as m . sand bottle water
1
3. The difference between m and 9. Use the formula to calculate the density of
1
m gives the mass of the sand. sand. That is,
(
0
Mass of sand = m − m ). m sand
1
0
4. Remove the stopper, add water ρ sand = V sand
into the bottle until the bottle is m
full, replace the stopper. ρ sand = V −V
sand
5. Measure the mass of the bottle bottle water
containing water and sand as m . Therefore, ρ = m −m 0 .
1
2
V
sand
1
2
bottle −(m −m )
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Physics Form 1 Final.indd 83 16/10/2024 20:56