10.1bFree
Your guide: Sir HamzaBelieves every formula has a story, and units never lie.
A heated liquid's molecules move faster and spread apart, so its volume increases: ΔV = β V0 ΔT. A liquid has no definite shape, so it expands freely in all directions.
A heated gas's particles hit the container walls more often and harder. In a rigid container the pressure rises. In a flexible one the volume grows and the pressure stays the same, as Charles' law says.
Heat a flask of liquid. First the glass expands, so the level falls from A to B: the expansion of the flask, AB.
Then the liquid expands and the level rises from B to C: the real expansion, BC. What you see from A to C is the apparent expansion, AC.
BC = AC + AB, so real expansion is always greater than apparent expansion.
A hot air balloon rises because the heated air inside expands and becomes lighter than the cooler air outside.
In a car engine, hot gases from burning fuel expand and push the pistons. Aerosol cans and gas cylinders can explode if heated.
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A heated liquid's molecules move faster and spread apart, so its volume increases: ΔV = β V0 ΔT. A liquid has no definite shape, so it expands freely in all directions.
A heated gas's particles hit the container walls more often and harder. In a rigid container the pressure rises. In a flexible one the volume grows and the pressure stays the same, as Charles' law says.
Heat a flask of liquid. First the glass expands, so the level falls from A to B: the expansion of the flask, AB.
Then the liquid expands and the level rises from B to C: the real expansion, BC. What you see from A to C is the apparent expansion, AC.
BC = AC + AB, so real expansion is always greater than apparent expansion.
A hot air balloon rises because the heated air inside expands and becomes lighter than the cooler air outside.
In a car engine, hot gases from burning fuel expand and push the pistons. Aerosol cans and gas cylinders can explode if heated.
What you see in a heated flask is the liquid's expansion minus the flask's. That is why the real expansion is larger than the apparent one.
Q1. A sealed steel cylinder of gas is left in the sun. What happens to the gas, and why is this dangerous?
The pressure rises and may burst the cylinder, so such containers are kept away from heat.
Q2. A flask of liquid is heated. The level first falls 2 marks, then rises 9 marks above where it started. Name AB, AC and BC.
BC = 9 + 2 = 11 marks of real expansion.
✗ The rise you see in the flask is the liquid's real expansion.
✓ That is the apparent expansion; add the flask's own expansion to get the real one.
✗ The first fall in level means the liquid shrank.
✓ The glass expanded first and made more room; the liquid did not shrink.
✗ A heated gas always gets bigger.
✓ In a rigid container its pressure rises instead.
1. In Fig. 10.3, real expansion BC equals:
(b) p. 5: BC = AC + AB.
2. When a flask of liquid is first heated, the level falls because:
(d) p. 4: the glass expands, so the level falls from A to B.
3. A gas is heated in a non-flexible container. Its:
(a) p. 5: increased collisions lead to a rise in pressure.
4. A hot air balloon rises because the heated air inside:
(c) p. 5 and Fig. 10.4.
5. Liquids expand more freely than solids because they:
(b) p. 4: liquids do not have a definite shape, so they expand freely in all directions.
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