Practical Skills in Physics

Working like a physicist

Physics is not only a set of facts. It is a way of finding things out by careful, fair testing, and the practical exam rewards those skills. This module works through the whole process: - Planning: choosing variables and a fair method.\n- Measuring: using the right apparatus correctly.\n- Analysing: repeats and the mean, tables, graphs and anomalies.\n- Concluding: drawing a sound conclusion from the evidence. The physics topics themselves are covered in the other modules. Here the focus is entirely on how to carry out and interpret an investigation.

Words for practical work

Five terms you need before you use them. Learn what each one means.

Match each instrument to what it measures

Accurate against precise

These two words are often mixed up, but they mean different things. A good experiment aims to be both.

Which is the control variable?

A student investigates how the length of a wire affects the current through it. Which of these is a control variable?

• The thickness of the wire, kept the same throughout
• The length of the wire, which is changed each time
• The current, which is measured as the result
• The reading shown on the clock

Tap the two things that make a test fair

Tap the TWO things that keep an investigation a fair test.

• Changing only one variable at a time
• Keeping the control variables the same
• Changing several variables at once
• Guessing the results in advance

Handling your data well

Good data handling turns a set of readings into a trustworthy result. A few habits make all the difference. Take repeat readings at each setting and work out the mean, which smooths out small errors. If one reading is far from the rest and clearly does not fit, treat it as an odd one and leave it out of that mean. Record everything in a clear table with the correct units, then plot a graph. A straight line passing through the origin shows that one quantity is in direct proportion to the other, and the shape of the line is often the clearest part of your evidence.

Pick the true facts about practical work

Select the TWO statements that are true.

• Taking repeat readings and averaging improves reliability
• A straight line through the origin shows direct proportion
• An anomalous result should always be kept in the mean
• The dependent variable is the one you deliberately change

Order how to plan and run an investigation

Put the stages of a good investigation in a sensible order.

• Write a hypothesis to test
• Identify the variables and plan a fair method
• Carry out a risk assessment
• Take repeat readings and record them in a table
• Plot a graph and draw a conclusion

One investigation, done well

Follow how Niamh investigated how far a spring stretches when weights are hung on it.\n\nPlanning: she decided to change the load on the spring and to measure the stretch each time, keeping the same spring and the same ruler throughout. Fair testing: by changing only the load and keeping everything else the same, she made sure the test was fair. Repeats: at each load she measured three times and took the mean, which made her results more trustworthy. Spotting the odd one: one reading was far larger than the rest and plainly did not fit, so she left it out of that mean. The conclusion: she plotted the stretch against the load, drew a straight line through the origin, and concluded that the stretch is in direct proportion to the load.

Complete the practical skills facts

The one factor you deliberately change is the _____ variable. The factor you measure to see the effect is the _____ variable. A factor you keep the same to be fair is a _____ variable. A reading that does not fit the pattern is an _____ result.

Work out the mean

A student takes five readings of a length in millimetres: 12, 14, 16, 18 and 50. One reading is clearly anomalous. Ignore the anomalous reading, then work out the mean of the other four readings.

Build a practical skills point

Choose the words that complete this statement about fair testing.

Improve the experiment

Read each situation and choose the best way to improve the investigation, then think about why.

• A student changes both the length and the thickness of a wire at the same time. What is wrong with this?
• One result sits far from all the others and does not fit the pattern. What should the student do?
• A student takes only a single reading for each measurement. How could the results be made more reliable?

Explain how to carry out a good investigation

A classmate is about to do their first physics investigation. Explain how to carry it out well using what this module has covered.

• Explain the three types of variable in an investigation
• Explain how to make a test fair
• Explain why repeat readings and a mean are useful
• Explain what to do with an anomalous result
• Finish by explaining how a graph helps you draw a conclusion