# Boyle's LawPage 2

#### WATCH ALL SLIDES

Curved lines are hard to recognise, so we plot the volume against the reciprocal of pressure (ie. 1/p)

This time the points lie close to a straight line through the origin.

This means volume is directly proportional to 1/pressure or

volume is inversely proportional to pressure

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## This leads us back to Boyle’s Law

Boyle’s Law: for a fixed mass of gas kept at constant temperature the volume of the gas is inversely proportional to its pressure.

Slide 12

## Problem

A deep sea diver is working at a depth where the pressure is 3.0 atmospheres. He is breathing out air bubbles. The volume of each air bubble is 2 cm2. At the surface the pressure is 1 atmosphere. What is the volume of each bubble when it reaches the surface?

Slide 13

## How we work this out

We assume that the temperature is constant, so Boyle’s Law applies:

Formula first: P1 x V1 = P2 x V2

Then numbers:= 1.0 x 2 = 3.0 x V2

Now rearrange the numbers so that you have V2 on one side, and the rest of the numbers on the other side of the ‘equals’ symbol.

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Here’s what you should have calculated

V2 = 3.0 x 2

1.0

therefore volume of bubbles = 6 cm3

Note that P1 and P2 have the same unit, as will V1 and V2

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