Practical Skills at A2 level (Question 2 - analysis)

Question 1

3

Determining gradient and y-intercept

Answer 1

1. Clearly lay out equation above y = mx + c
2. Figure out which quantity relates to which part of the equation
3. State gradient and y-intercept

Question 2

Table

Answer 2

Significant figures of calculated value should equal the significant figures of the first column

Uncertainty should be rounded to match the precision of the calculated value
(eg. 25.6 ± 0.3, 25 ± 4)

Absolute uncertainty is calculated by multiplying the percentage uncertainy of the value by the calculated value
(eg. ± 5%, 83 ± 4
83 x 0.05 = 4.15 ∴ absolute uncertainty is 4)

Absolute uncertainty is always to 1sf

Question 3

Log/Ln in tables

Answer 3

The log/ln of a value should have the same number of dp as there is sf in the original uncalculated value

To determine the uncertainty take the upper limit of the calculated value and subtract it from the lower limit of the calculated value and didvide it by 2

(eg. M = 4.8 ± 0.4
lg(M) = 0.68 ± 0.04, [lg(5.2) - lg(4.4)] / 2 = 0.04 )

Question 4

4

Graph

Answer 4

1. Plot 6 points correctly to half a small square, with point diameter no larger than half a small square
2. All error bars plotted correctly and symetrically, with length accurate to half a small sqaure
3. Line of best fit drawn and labelled LOBF, with 3 points above and 3 points below, does not need to go through all error bars
4. Line of worst fit drawn and labelled LOWF, going through all error bars with either steepest or shallowest gradient possible

Question 5

Determining gradient and uncertainty

Answer 5

Gradient of LOBF taken from 2 points far away from eachother and the coordinates of the points used must be stated on the graph

Gradient of LOWF taken from 2 points far away from eachother and the coordinates of the points used must be stated on the graph

Gradient is the gradient of the LOBF and the uncertainty is the gradient of the LOBF minus the gradient of the LOWF

Same procedure for y-int is y-int of LOBF and uncertainty of y-int is the y-int of LOBF - y-int of LOWF

For y-int if graph has false origin, sub values into equation to find y-int

Make sure points from LOBF are labelled with LOBF and points from LOWF are labelled with LOWF

Question 6

Last page questions

Answer 6

Percentage uncertainties are added, if the operation is division or multiplication, percentages are multiplied by the exponent of the value (if used)

Total absolute uncertainty is calculated by adding together percentage uncertainties then converting it to an absolute uncertainty

Absolute uncertainties always increase with further calculations

To obtain the absolute uncertainty from the percentage uncertainty, multiply the decimal of the percentage uncertainty by the value