StemUp: A level STEM General Practical

What is an independent variable? (2)

- An independent variable is the variable that is changed in an experiment.

- This is done to test its effects on the dependent variable.

What is a dependent variable? (2)

- A dependent variable is the variable that is measured in an experiment.

- This variable is affected by the independent variable.

What are controlled variables? (2)

- Controlled variables are factors that are kept constant during an experiment.

- These ensure that any any changes in the dependent variable are due to the independent variable only.

What is the mean of a data set? (2)

- The mean is a measure of average.

- This is the sum of all values divided by the number of values in the data set.

What are qualitative observations? (2)

- Qualitative observations are observations that deal with descriptions.

- For example, this would include colours.

What are quantitative observations? (1)

Quantitative observations are numerical values.

What is accuracy? (2)

- Accuracy describes how close a reading is to the true value.

- A value is considered accurate if it is close to the true result.

How do you interpret volumes? (1)

- When reading volume from a measuring cylinder or syringe, take the measurement from where the meniscus is.

How do you reduce random errors in measurements? (3)

- To reduce random errors, take multiple measurements and calculate an average.

- Use more precise instruments.

- Increase sample size.

What is the uncertainty in a measurement? (2)

- Uncertainty is the range within which the true value is expected to lie.

- This is given by the precision of the instrument used and the repeatability of the measurements.

How do you calculate the percentage uncertainty of a measurement? (1)

To calculate the percentage uncertainty use

(Absolute uncertainty / Measurement value) x 100.

What should you include when drawing a graph in an experiment? (4)

- Labelled axes (with units).

- Title.

- Line of best fit.

- Data points plotted (with error bars if applicable).

What is the purpose of a control experiment? (3)

- A control experiment is used to compare results.

- This helps to confirm that the effect on the dependent variable is due to the independent variable alone.

- This ensures that the results were obtained without any interference from other factors.

How do you ensure an experiment is reliable? (3)

- To ensure an experiment is reliable, repeat the experiment multiple times.

- Maintain consistent controlled variables.

- Use precise instruments.

What are systematic errors? (2)

- Systematic errors are consistent, repeatable errors.

- They are caused by faulty equipment or flawed experimental design.

How can systematic errors be minimised? (3)

- Calibrate instruments.

- Use appropriate methods.

- Cross-check results with different methods.

Why is it important to calibrate instruments before taking measurements? (3)

- Calibrating instruments ensures that they provide accurate readings.

- This is done by comparing them to a known standard.

- Thereby, systematic errors are reduced.

What is a colorimeter? (2)

- A colorimeter is apparatus that measures light absorbance or light transmission.

- It is used to measure colour change.

What questions are asked in a risk assessment? (3)

- What could harm you?

- What harm could it cause you?

- What actions could be put in place to prevent / treat harm?

What are some ways in which pH is measured? (3)

BIOLOGY AND CHEMISTRY ONLY

- Indicator paper.

- Indicator solution.

- pH metre.

How is length measured? (2)

- Ruler.

- Tape measure.

What needs to be considered when measuring length? (2)

- The scale needs to be considered.

- High enough precision of equipment should be ensured.

How is temperature measured? (2)

- Thermometer.

- Data logger.

How is volume of a gas measured? (1)

Gas volume is measured using a gas syringe.

How is volume of a solution measured? (2)

- Measuring cylinder.

- Syringe.

How is time measured? (1)

Time is measured using a stop watch.

How is mass measured? (1)

Mass is measured using balances/scales.

What is an anomaly? (2)

An anomaly is an outliner in a set of results

What is standard deviation? (2)

- Standard deviation measures the spread of data around the mean value.

- This is useful when comparing consistency between different data sets.