The method and the results are on the ideal gas equation lab. Do the analysis yourself first, then check the answers below.
Quick answer: An ideal gas obeys pV = nRT, where pressure, volume and kelvin temperature are linked through the amount of gas. These answers go with the Physics 11-12 lab on ideal gas equation: the graph, the calculations, the uncertainties and the conclusion explained, for all 8 analysis questions.
The sample data give a straight line with a gradient near 0.34 kPa/°C and an intercept at 94.0 kPa. The values below use these numbers, so your own results will differ slightly depending on your readings.
Level: Physics grades 11-12 (A Level · IB · Class 11-12) · Curriculum: IB B.1-B.3
The points lie close to a straight line with a positive gradient that does not pass through the origin. The pressure increases by equal steps for equal temperature steps, so p increases linearly with θ: p = mθ + c.
At p = 0: θ = −c / m = −94.0 / 0.34 = −276 °C. A least-squares fit of the six points gives m = 0.345 kPa/°C and c = 93.9 kPa, so θ = −272 °C, consistent with this estimate.
Question 4 Comparing with the accepted value
Difference = 3 °C. Percentage difference = (3 / 273) × 100 = about 1 %. The experiment agrees well with the accepted value of −273 °C.
Question 5 Why kelvin is better
For a fixed amount of gas at constant volume, pV = nRT gives p = (nR/V)T, so p is proportional to the kelvin temperature. In degrees Celsius T = θ + 273, which adds a constant, so p = (nR/V)(θ + 273) is linear but has an intercept. Proportionality holds only from the absolute zero of the scale.
Question 6 Sources of error
Any two of: air in the tube and gauge is at room temperature, not the bath temperature (so not all the gas is heated); the air inside lags behind the thermometer reading; the bung leaks slightly; the gauge has poor resolution; the thermometer is in the bath, not in the flask. These shift the intercept and gradient.
Question 7 Uncertainty in temperature
Percentage uncertainty = (1 / 20) × 100 = 5 %. At 100 °C it would be only 1 %. The uncertainty matters more at low temperatures, where the reading is smaller.
Question 8 Improving the method
Any two of: stir for longer so the gas reaches the bath temperature; put the whole flask and tube in the bath; use a digital probe with 0.1 °C resolution; take more readings and repeat each; extend the range with a colder salty-ice bath. Less systematic error gives a more reliable estimate of absolute zero.
