Types of Variables

1. What is meant by the term independent variable?
2. What is meant by the term dependent variable?
3. What is meant by the term control variable?
4. In the spring extension required practical, what is the independent variable?
5. In the spring extension required practical, what is the dependent variable?
6. Give two control variables in the spring extension required practical.
7. Explain why control variables must be kept the same throughout an investigation.
8. A student investigates how the voltage across a lamp affects the current through it. Identify the independent variable and the dependent variable.
9. A student investigates how the height of a ramp affects the speed of a toy car. Give one independent variable, one dependent variable and one control variable.
10. A student investigates how the temperature of water affects the time taken for a sugar cube to dissolve. Identify the independent variable, dependent variable and two control variables.

Answers to Types of Variables

1. The independent variable is the variable that is changed by the investigator.
2. The dependent variable is the variable that is measured during the investigation.
3. A control variable is a variable that is kept the same throughout the investigation.
4. The independent variable is the force (or weight) applied to the spring.
5. The dependent variable is the extension of the spring.
6. Any two from: use the same spring, keep the ruler vertical, keep the pointer horizontal.
7. Control variables must be kept the same so that any changes in the dependent variable are caused only by changes in the independent variable.
8. Independent variable: voltage across the lamp. Dependent variable: current through the lamp.
9. Independent variable: height of the ramp. Dependent variable: speed of the toy car. Control variable: same toy car.
10. Independent variable: temperature of the water. Dependent variable: time taken for the sugar cube to dissolve. Control variables: size of the sugar cube and volume of water.

Random Errors

Random Errors GCSE Questions

1. What is an accurate measurement?
2. In an experiment, why is it important for a measurement to be close to the true value?
3. A student reads a thermometer while looking straight at the top of the liquid. Why is this the correct way to read it?
4. What is parallax error?
5. A student looks down at the liquid in a thermometer and records 56 °C instead of 55 °C. What type of error has happened?
6. A second student looks up at the liquid in a thermometer and records 54 °C instead of 55 °C. Why is this reading less accurate?
7. What are random errors?
8. Why can random errors cause variation in results?
9. Give one example of random error when using a thermometer.
10. Give one example of random error when using a stopwatch.
11. Why might different students get slightly different times when timing the same experiment?
12. Why can a digital thermometer reduce parallax error?
13. Students measure the highest temperature reached when magnesium reacts with acid. Why might their temperature readings vary each time?
14. Students cut strips of magnesium for an experiment. Why might this introduce random error?
15. Why can random errors never be completely avoided?
16. How can scientists reduce the effect of random errors?
17. Why should students repeat measurements in an experiment?
18. What is calculated after taking repeat measurements?
19. Why does calculating a mean help improve the reliability of results?
20. Why should GCSE students avoid using the phrase “human error” in exam answers?

Answers to Random Errors

1. An accurate measurement is one that is close to the true value.
2. It is important because it makes the result more reliable and useful.
3. This avoids parallax error and gives a more accurate reading.
4. Parallax error is caused when a scale is read from the wrong angle.
5. Parallax error has happened.
6. The student is viewing the thermometer from the wrong angle.
7. Random errors are unpredictable errors that cause results to vary.
8. They cause results to be slightly higher or lower each time.
9. Reading the thermometer from slightly different angles each time.
10. Starting or stopping the stopwatch at slightly different times.
11. Different students have different reaction times.
12. A digital thermometer shows a number on a display, so there is no scale to read from an angle.
13. Students may read the thermometer slightly differently each time.
14. The strips may not all be cut to exactly the same length.
15. Small variations happen naturally when taking measurements.
16. Scientists can take repeat measurements and calculate a mean.
17. Repeats help reduce the effect of random errors.
18. A mean value is calculated.
19. It reduces the effect of unusually high or low readings.
20. GCSE exam answers should use scientific terms such as random error, not human error.

Repeatable and Reproducible Measurements

The questions below relate to this free science lesson video

Repeatable and Reproducible Measurements GCSE Questions

1. What is meant by a reactant?
2. What is the aim of a rate of reaction practical?
3. In the marble chips and acid experiment, what gas is produced?
4. How can the volume of gas produced be measured?
5. Why is the gas collected in an upturned measuring cylinder?
6. What fixed volume of gas could students choose to measure in this experiment?
7. What happens to the time taken when the concentration of acid is increased?
8. What happens to the rate of reaction when the concentration of acid is increased?
9. Why might repeat results be slightly different from each other?
10. What is meant by random error?
11. What is meant by repeatable measurements?
12. If one student repeats an experiment three times under the same conditions and gets similar results, what word describes the measurements?
13. In the disappearing cross experiment, where is the cross placed?
14. Why does the cross eventually disappear from view?
15. What is a precipitate?
16. How can the disappearing cross experiment be used to measure rate of reaction?
17. What happens to the time taken for the cross to disappear when concentration is increased?
18. What is meant by reproducible measurements?
19. If two different students use different equipment but get similar patterns in their results, what word describes the measurements?
20. What is the main difference between repeatable and reproducible measurements?

Answers

1. A reactant is a chemical that takes part in a reaction.
2. The aim is to investigate how a factor affects the speed of a reaction.
3. Carbon dioxide gas is produced.
4. The gas can be collected and measured using an upturned measuring cylinder.
5. The gas collects at the top and pushes the water down.
6. Students could measure the time taken to produce 20 cm³ of gas.
7. The time taken decreases.
8. The rate of reaction increases.
9. Repeat results may be slightly different because of random errors.
10. Random errors are unpredictable small variations in measurements.
11. Repeatable measurements are similar results obtained by the same person using the same method and equipment.
12. The measurements are repeatable.
13. The cross is placed on a piece of paper underneath the conical flask.
14. The cross disappears because a cloudy precipitate forms.
15. A precipitate is an insoluble solid formed in a reaction.
16. Students time how long it takes for the cross to disappear.
17. The time taken decreases.
18. Reproducible measurements are similar results obtained by different people or using different equipment.
19. The measurements are reproducible.
20. Repeatable means the same investigator gets similar results, while reproducible means different investigators get similar results.