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## Physics Tutorials

### Boyle’s Law and Lungs

Boyle’s Law states that pressure and volume of an ideal gas trapped in an enclosure are inversely proportional.

The concept of Boyle’s Law is that when the pressure of a gas is increased or decreased, the volume of the gas changes inversely proportional to it. A gas that has an increase in pressure, will have a decrease in its volume. A gas that decreases in pressure will increase in volume. Therefore, it is inversely proportional. The formula used for Boyle’s Law is P1V1=P2V2, where volume 1 and pressure 1 are values before manipulation and volume 2 and pressure 2 are values after. The product, PV, is constant only while the gas is behaving like an ideal gas.

A sealed syringe works in accordance to Boyle’s Law. When the syringe top is pulled, the volume is increased while the pressure is decreased. When the top of the syringe is pushed, the volume is decreased and the pressure inside the syringe is increased.

Another example that applies Boyle’s Law is our lungs. A cardinal rule in scuba diving is to not hold your breath. A diver at a depth of 10 m experiences significant water pressure which collapses the chest cavity. As the diver surfaces, the pressure decreases, and the air trapped in the lung expands. The safe practice is to continue breathing to allow the air to escape. If the diver holds her breath, lungs sustain serious injury.

#### EXAMPLE

When 50 mL chlorine gas is compressed from 20 atm to 80 atm of pressure, what is the new volume of the chlorine gas?

SOLUTION:
Using the formula P1V1=P2V2 solve the question.
P1= pressure 1
V1= volume 1
P2= pressure 2
V2=volume 2

20x50=80V2
1000=80V2
V2=1000/80
V2=12.5 mL

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