1.1.4Development of Practical Skills in Physics
Investigative Approaches and Methods
5 min read 9 parts Lesson 5 of 29 1 quiz Virtual lab
1.1.4 Investigative Approaches and Methods — OCR A Level Physics A notes: Choose between different types of investigation and select appropriate methods for collecting evidence in physics.Not all physics investigations take the same form.
- Fair-test or controlled experiments
- Determination of a constant
- Observational or survey methods
- Modelling and simulation
- Primary data
- secondary data
Section 1 of 9Types of investigation
Not all physics investigations take the same form. Common approaches include:
- where one variable is changed and another measured.
- (for example current against potential difference for a component)
- where a quantity such as g, the specific heat capacity of a metal or the wavelength of light is found from a graph or equation.
Section 2 of 9Choosing a method
The method should match the question.
When a quantity is too small, too fast or too slow to measure directly, think of an indirect method: measuring the combined thickness of many sheets of paper; timing many oscillations; using light gates or video analysis for fast motion.
Section 3 of 9Primary and secondary data
Primary data are collected by the experimenter, and secondary data come from other sources, such as published tables of the speed of sound or the half-life of a nuclide. Secondary data are useful for comparison but their reliability must be checked: who measured them, how, and with what uncertainty. A conclusion is stronger when it is supported by both.
Section 4 of 9Qualitative and quantitative evidence
Quantitative data are numerical; qualitative data are descriptive, such as the colour of a flame or whether a wave pattern is clear. In physics numerical evidence is usually preferred because it allows a calculation of uncertainty and a graphical test. Qualitative observations can still support a plan, for instance to note that a wire glows red at a high current.
Section 5 of 9Testing a hypothesis
Experiments cannot prove a theory; they can support it or show it is wrong.
Section 6 of 9Data loggers, video and simulation
Modern investigations often use electronic methods.
- where the time between frames is known from the frame rate.
- such as radioactive decay or planetary orbits,
- and results from a model can be compared with experimental data.
When evaluating which approach to use, compare them on cost, time, precision and safety.
Section 7 of 9Worked examples
Describe how to determine the acceleration of free fall g using a drop of height h and time t, and what graph to plot.
Release a steel ball from an electromagnet at height h (metre rule). Start a timer as the ball is released and stop it as it hits a trapdoor switch. Repeat three times for each of at least six heights.
Since h = ½gt2, plot h (y) against t2 (x). The gradient is ½g, so g = 2 × gradient.
A graph of h against t2 has gradient 4.85 m s−2. Find g.
g = 2 × 4.85 = 9.70 m s−2.
This differs from 9.8 by about 1%, which would be commented on in terms of the uncertainty in timing.
Section 8 of 9Key terms
| Term | Meaning |
|---|---|
| Primary data | Data collected directly by the experimenter. |
| Secondary data | Data obtained from published or other sources. |
| Quantitative | Expressed as numbers with units. |
| Qualitative | Descriptive and not numerical. |
| Hypothesis | A testable prediction based on theory. |
| Indirect method | Finding a quantity by measuring others and calculating. |