Design experiments, identify variables, and assess risks like a professional physicist
In OCR written papers, you'll be given a scenario or experiment and asked to plan how you would conduct it. You won't actually perform the experiment, but you need to demonstrate that you understand the method, the variables involved, and potential safety concerns.
Questions typically ask you to:
Planning questions are worth 4-6 marks and appear in Papers 1, 2, and 3. Students often lose marks by: not being specific enough (e.g., saying "use a ruler" instead of "use a metre rule with mm precision"), forgetting control variables, or not explaining why a piece of equipment is suitable.
A hypothesis is a testable prediction about the relationship between variables.
Good hypothesis format:
"As [independent variable] increases, [dependent variable] will increase/decrease because..."
Example:
"As the length of a pendulum increases, the time period will increase because T ∝ √L according to the equation T = 2π√(L/g)"
Exam tip: Always link your hypothesis to a physics principle or equation if possible.
Independent Variable (IV): The variable YOU change
Dependent Variable (DV): The variable YOU measure (responds to the IV)
Control Variables: Everything you keep constant to ensure a fair test
Example - Measuring resistance of a wire:
Common mistake: Confusing IV and DV, or forgetting control variables entirely!
You must justify WHY you chose each piece of equipment based on:
Example:
"Use a digital stopwatch (resolution 0.01s) rather than analog (resolution 0.1-0.5s) to measure the time period of a pendulum because smaller time intervals need greater precision."
Equipment specifications to know:
For every hazard, identify:
Common hazards in A-Level physics:
| Hazard | Risk | Control |
|---|---|---|
| High voltage (>50V) | Electric shock | Use insulated wires, keep hands dry, emergency cut-off switch |
| Heavy masses | Falling objects, foot injury | Wear safety shoes, clamp securely, sand tray underneath |
| Lasers | Eye damage | Never look directly at beam, wear laser safety goggles, warning signs |
| Hot objects | Burns | Use heat-proof mats, tongs, allow cooling time |
| Radioactive sources | Radiation exposure | Use tongs, store in lead-lined box, minimize exposure time, stand behind barrier |
Exam format: "State one hazard and one safety precaution for this experiment." [2 marks]
Question:
A student wishes to determine the acceleration due to gravity (g) by dropping a steel ball bearing and measuring its time of fall. Plan this experiment.
Model Answer:
Mark Scheme:
Question:
Describe how to determine the resistivity (ρ) of a constantan wire.
Model Answer:
Mark Scheme:
Practice identifying independent, dependent, and control variables in different experiments
🚧 Simulation coming soon • ID: variable-identifier
A student investigates how the extension of a spring varies with applied force. Which of the following is the independent variable?
A: Extension of spring
B: Applied force
C: Spring constant
D: Material of spring
Answer:
Explanation:
The independent variable is what YOU change. The student applies different forces (B) and measures the resulting extension (dependent variable).
A student plans to investigate the relationship between the angle of a ramp and the acceleration of a trolley. State the independent variable, dependent variable, and two control variables.
Answer:
A student wishes to investigate how the time period T of a simple pendulum depends on its length L. Plan an experiment to test the hypothesis that T ∝ √L. Your answer should include: variables, equipment with justifications, a method, and how to process the data.
Answer: