# PV diagrams for ideal gas

## Homework Statement

Imagine a graph of pressure in kPa (y-axis) against volume in L (x-axis). There is a straight line moving from point A at 300kPa, 0.5L to point B at 500kPa, 1L. The false origin on this graph is 200kPa, 0L. What is the work done by the gas?

W=pV

## The Attempt at a Solution

I know that work is area under graph so its basically the area of a triangle plus area of trapezium. But this gives work = 100J but textbook says 200J. Where have I gone wrong?

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ehild
Homework Helper
See the picture . You need the blue area from the really zero pressure.

ehild

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Andrew Mason
Homework Helper

## Homework Statement

Imagine a graph of pressure in kPa (y-axis) against volume in L (x-axis). There is a straight line moving from point A at 300kPa, 0.5L to point B at 500kPa, 1L. The false origin on this graph is 200kPa, 0L. What is the work done by the gas?

W=pV

## The Attempt at a Solution

I know that work is area under graph so its basically the area of a triangle plus area of trapezium. But this gives work = 100J but textbook says 200J. Where have I gone wrong?
Use the formula for area of a trapezoid: (L1 + L2)/2 x W

AM

Last edited:
ehild
Homework Helper
Use the formula for area of a parallelogram: (L1 + L2)/2 x W

AM
You meant trapezoid, I think ehild

Andrew Mason
You meant trapezoid, I think 