2.2 Making Measurements and Analysing Data

Specification Point 2.3 OCR A Physics A-Level

What is the typical value for the mass of a person

70kg

What is the typical value for the mass of a car

1500kg

What is the typical value for the height of a man

1.8m

What is the typical value for the walking speed

1.5ms^-1

What are the 2 types or errors

Random errors

Systematic errors

What is a random error

Random errors cause readings to be spread about the true value due to the results varying in an unpredictable way.

What does a random error effect

Precision

Can you completely prevent random errors

No you can try lessen their effect but can never completely remove them

Name 2 examples of a random error

Different head position when reading of a ruler

Can’t keep the control variables the same

How can you lessen the effects of random errors

-Use more sensitive apparaturs

-Repeating measurements and finding the mean

What is a systematic error

Systematic errors usually cause readings to be different to the true value by the same amount

What does systematic errors effect

Accuracy

Name 2 examples of systematic errors

-Using an inaccurate scale

-Repeating the same mistake

Can systematic errors be removed completely

Yes with proper scientific technique systematic errors can be removed and cause negligible effects on your experiment

How can you remove systematic errors

Calibrate the apparatus to make sure there is no 0 error

What is the absolute uncertainty

The total uncertainty for a measurement

What is the percentage uncertainty

The uncertainty given as a percentage of a measurement

How do you calculate the absolute uncertainty

Or determine if the calculation is a reading or a measurement and if its been taken by a digital or analogue apparatus

Digital = the uncertainty is the resolution of the equipment

Analogue = half the uncertainty of the equipment

Reading = only taken once

Measurement = taken twice so uncertainty is doubled

How to calculate the percentage uncertainty

What is the order of magnitude

Rounded up to the nearest power of 10

What amount of significant figures should you give your answer to

The smallest number of significant figures in the question.

How do you add or subtract uncertainites

Add the absolute uncertainites

How do you multiply or divide uncertainites

You add the percentage uncertainties

How do you raise an uncertainty to a power

You multiply the percentage uncertainty by the power

What is the percentage difference

If you know the true value and want to measure the accuracy of your results you can use the percentage difference

What is the calculation for percentage difference

What is the definition of precise

The smaller the amount of spread of your data from the mean the more precise it is

What is the definition of repeatable

If you can repeat the experiment multiple times and get the same results

Definition of reproducible

If someone else can do the experiment and get the same results as you

What is a valid result

A result that answers the question using precise data

What does an error bar show

The uncertainty on a graph

How do you find the uncertainty from a gradient

Draw a line of worst fit

What 2 worst fit lines are there

A maximum worst fit

A minimum worst fit

How do you draw a line of worst fit

Going through all the error bars