Working as a Physicist

What do good results have to be

Valid, precise, repeatable and accurate

Valid result

You have measured what you are meant to as all variables are controlled

Precise result

The range is small

Repeatable result

You can repeat an experiment multiple times and get the same results

Reproducible result

A different experimenter using different equipment and different methods can obtain similar results

Accurate result

The result is very close to the true value

Error

The difference between your measured value and the true value of whatever your measuring

Systematic error

A consistent difference between the measured values and the true values

What do systematic errors affect

-Accuracy

-Reproducibility

What don’t systematic errors affect

-Validity

-Precision

-Repeatability

How to counter systematic errors

Check the apparatus at the start of the experiment

Random error

When results vary around the true result in an unpredictable way

What do random errors affect

-Validity

-Precision

-Repeatability

-Reproducibility

-Accuracy

How to counter random errors

-Better resolution on apparatus

-Control variables more

-Do more repeats

Conclusion

Explains what the data shows

What are the limitations to a conclusion

-You can only make it if you have valid results

-Limited to the circumstances it was tested under

-Evaluate the quality of your results

-Consider how the experiment could be improved

How to improve precision

Use a computer to collect data

What is the smallest uncertainty due to

Resolution of equipment

How to calculate uncertainty due to equipment resolution

± half of the smallest division on the measuring equipment

What does uncertainty give you

The margin of error

Absolute uncertainty

The total uncertainty for a measurement

Percentage uncertainty

Uncertainty as a percentage of the measurement

Uncertainty on a mean

The largest difference between the mean and any calculated values

How to calculate uncertainty on a mean

Half the range

if no uncertainty is given, what is the assumed uncertainty

Half the increment of the last significant figure the value is given to

How to deal with uncertainties when adding/subtracting data

Add the absolute uncertainties

How to deal with uncertainties when multiplying/dividing data

Add the percentage uncertainties

How to deal with uncertainties when raising to a power

Multiply the percentage uncertainty by the power

How to show the uncertainty of individual points

Use error bars

What is this

Error box

How to find uncertainty from a graph

Draw an error bar and two lines for the maximum and minimum possible slops

How to find the uncertainty of any point on a graph

Find the difference between the maximum and minimum slope and halve it

How to find the uncertainty in the gradient

Half of the difference between the gradients of the maximum and minimum slopes

Variable

Anything that has the potential to change in an experiment

Independent variable

The thing you change

Dependent variable

The thing you measure

How to ensure your control variables have not messed up your experiment

Measure your control variables too and work out whether they are changing

What to consider when choosing apparatus

-Units of measurements

-Range of measurements

-What the apparatus measures

-Risks of apparatus

What should you do when recording data in a table

-Discard anomalous results

-Average the repeated measurements

Qualitative data

Data that can be given a numerical value

Quantitative data

Data that cannot be given a numerical value

Questions when evaluating an experimental design

-Does the experiment actually test what it is meant to

-Is the method clear enough for someone else to follow

-Is everything controlled

-Are the apparatus and techniques appropriate

-Are enough repeated measurements taken

-Is the experiment going to be conducted safely

-Ethical/environmental considerations

When should you discard anomalous results

If there is a good reason

How should significant figures be handled when analysing data

Give any values to the same number of significant figures as the data value with the lowest significant figures

What is the problem with giving a result to too many significant figures

You are saying that the final result is more precise than it is

Which axis should the independent variable go on

x-axis

Which axis should the dependent variable go on

y-axis

How should points be plotted on the graph

With a sharp pencil

Why should points be plotted onto a graph with a sharp pencil

They are as accurate as possible

How should a line/curve of best fit be drawn

Around half of the data points are above the line and around half of the data points are below the line, excluding anomalous results

Positive correlation

As one variable increases, the other increases

Negative correlation

As one variable increases, the other decreases

No correlation

No relationship between the variables

Linear

The line of best fit is straight

Linear graph equation

y = mx + c

What does it mean if y is proportional to x

The graph is linear and passes through the origin

How to find the gradient of a curved graph

Draw a tangent

Order of the scientific process before report

1- Ask a question

2- Suggest an answer by forming a theory (and form a model)

3- Make a prediction or hypothesis

4- Carry out a test

Theory

A possible explanation of observations

Model

A simplified picture of what’s going on

Prediction/hypothesis

Specific, testable statement, based on the theory, about what might happen in a test situation

Why is a test carried out

To provide evidence to support your prediction

Order of scientific process after report

1- Results of the test are noted in a report

2- Report is sent out to peers who peer review

3- Results are published in scientific journals

4- Other scientists test theory with the same experiment

5- Then use the theory to make new predictions and test them with new experiments

6- If all evidence supports the theory, it is accepted

Scientific journals

Where scientists publish their findings

Scientific report

A published finding from a scientist after a test provides evidence for their theory

What are scientific reports also called

Papers

Why must a peer review be conducted

The integrity of the report must be checked as a scientist may be dishonest or biased

Peer

An expert in the area of which a report has been sent

Peer review

Peers examine the data and results of the scientific report and check if the conclusion is reasonable

Is a scientific fact ever a fact

No

Why is scientific fact never a fact

Scientific breakthroughs may provide new ways to answer the question

How is evidence obtained

Controlled experiments in laboratories

Why are experiments performed in laboratories

It is easiest to control variables there

Why should experiments be controlled

So that the only effects seen are linked to the independent variable

What happens if a relationship between independent and dependent variable is found

Do not conclude yet as the effect and independent variable could just be correlated

Causal relationship

The effect seen is caused by changing a variable

In what ways does science affect society

-Economically

-Socially

-Environmentally

How does science affect society economically

-Society has to consider the cost of implementing changes after scientific discoveries (e.g. climate change)

-Government has to justify spending money on research

How does science affect society socially

Decisions based on science may affect lives (e.g. nuclear power plants)

How does science affect society environmentally

Some scientific implementations may be more harmful to the environment than others

Base quantity

Quantities from which all other quantities can be derived

What does SI stand for

Système International

State the base quantities

-Mass

-Length

-Time

-Current

-Temperature

-Amount of substance

-Luminous intensity

Mass SI unit

Kilogram

Length SI unit

Metre

Time SI unit

Second

Current SI unit

Ampere

Temperature SI unit

KelvinmoA

Amount of substance SI unit

Mole

Luminous intensity SI unit

Candela

Kilogram abbreviation

kg

Metre abbreviation

m

Second abbreviation

s

Ampere abbreviation

A

Kelvin abbreviation

K

Mole abbreviation

mol

Candela abbreviation

cd

Femto

10^-15

Pico

10^-12

Nano

10^-9