Working Scientifically
Working scientifically is the set of practical and mathematical skills used across all 13+ Common Entrance Science, including identifying variables, planning fair tests, choosing and reading apparatus correctly, and processing results such as means, anomalies, rates and percentage change. It is assessed both through stand-alone questions and embedded within biology, chemistry and physics questions on the ISEB papers.
Method
- Identify the independent variable (the one changed), the dependent variable (the one measured) and the control variables (the ones kept the same) in any investigation described.
- Choose the correct apparatus and unit for each measurement, for example a measuring cylinder in cm^3, a thermometer in degrees C, or a balance in g.
- Read scales carefully at eye level to avoid parallax error, taking the reading level with the bottom of a curved meniscus for liquids.
- Repeat measurements, identify any anomalous results (values that do not fit the pattern) and calculate a mean using only the consistent readings.
- For rate and percentage change calculations, find the change in the quantity first, then divide by the total time (for rate) or by the original value (for percentage change), and multiply by 100 for a percentage.
- Remember that a correlation between two variables does not prove that one causes the other; a third factor could explain both trends.
Worked example
A student measures the time for a ball to roll down a ramp three times: 3.24 s, 3.31 s and 3.18 s. (a) Calculate the mean time, giving your answer to 3 significant figures. (b) State why it is good scientific practice to repeat a measurement more than once.
- Add the three readings together: 3.24 + 3.31 + 3.18 = 9.73.
- Divide by the number of readings: 9.73 / 3 = 3.243333...
- Round to 3 significant figures: 3.24 s.
- For part (b), repeating a measurement allows anomalies to be spotted and a mean to be calculated, which makes the result more reliable.
- Final answer: mean time = 3.24 s; repeating measurements improves reliability by allowing anomalies to be identified and a mean found.
Practice questions
Try each question, then tap to reveal the answer.
Exam-style questions
Written in the style of a 13+ Common Entrance exam paper, with a full mark scheme.
Match each term to its correct definition. Terms: 1. Precision 2. Validity. Definitions: A. How close repeated measurements are to each other, regardless of whether they are close to the true value. B. Whether an investigation measures what it is actually intended to measure, with all variables other than the independent variable properly controlled.
Over several decades, both the number of smartphones owned in the UK and the number of people who wear glasses have increased. A student concludes that owning a smartphone causes people to need glasses. (a) State the type of relationship shown by this data. (b) Explain why the student's conclusion is not justified.
Kofi investigates the reaction between a 4 cm strip of magnesium ribbon and 40 cm^3 of dilute hydrochloric acid. He collects hydrogen gas in a gas syringe every 10 seconds. Time (s): 0, 10, 20, 30. Volume of gas (cm^3): 0, 16, 28, 34. (a) State the independent variable and the dependent variable in this investigation. (b) Calculate the rate of gas production between t = 0 s and t = 20 s, in cm^3/s. Give your answer to 2 significant figures. (c) State one hazard in this experiment and a suitable control measure.
Free printable worksheet
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