1.1.6States of Matter
Investigating Force and Extension — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions
5 min read 5 parts Lesson 3 of 30 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 5Variables and Apparatus
A fair test depends on changing one variable and measuring the effect, while keeping the others the same.
Independent variable
- Independent variable The force applied to the spring, changed by adding masses to a hanger, with the weight of each mass found using W = m × g.
Dependent variable
- Dependent variable The extension of the spring, found from the final length minus the original length and read from a ruler.
Control variable
- Control variable The spring itself, kept the same throughout, so that its spring constant does not change during the test.
Resolution
- Resolution The smallest change a measuring instrument can detect, so a ruler with 1 mm resolution limits how precisely the length is read.
Section 2 of 5Method
Repeating the readings and taking averages reduces the effect of random errors.
1
Record the unloaded length of the spring against the ruler, using a pointer fixed to the lower end of the spring.
2
Add a 100 g mass to the hanger, wait until the spring is still, and record the new length and the total mass in kilograms.
3
Repeat, adding a further 100 g each time until all the masses have been added, recording the mass and length every time.
4
Remove the masses and repeat the whole procedure until there are three complete sets of results, then average the lengths.
Section 3 of 5Analysis and Evaluation
Analysis and Evaluation
Processing
- Processing Convert each mass into a force using F = m × g with g = 9.8 N/kg, and each length into an extension.
Graph
- Graph Plot force against extension and draw a line of best fit, using the straight region of the graph to show proportionality.
Parallax
- Parallax Read the ruler at eye level, since reading from an angle causes a systematic parallax error.
Limit
- Limit Keep the forces small, because stretching beyond the limit of proportionality means the spring no longer obeys the relationship.
Section 4 of 5Worked Example
Question
- A spring has an original length of 12.0 cm.
- Readings are taken for masses of 0.100 kg, 0.200 kg and 0.300 kg, giving lengths of 14.0 cm, 16.0 cm and 18.0 cm.
- Calculate the force and extension for the 0.300 kg mass, and the spring constant.
- ForceF = m × g = 0.300 × 9.8 = 2.94 N.
- Extensione = 18.0 − 12.0 = 6.0 cm = 0.060 m.
- Spring constantk = F ÷ e = 2.94 ÷ 0.060 = 49 N/m.
- Check0.100 kg gives 0.98 N and an extension of 0.020 m, which again gives 49 N/m, so the relationship is proportional.
Answer For 0.300 kg, F = 2.94 N and e = 0.060 m, giving k = 49 N/m.
Section 5 of 5Exam Checklist & Tips
1.1.6 – Key Points for the Exam
- Independent variable The variable the experimenter changes on purpose.
- Dependent variable The variable measured to see how it responds to the independent variable.
- Control variable A variable kept constant so that it does not affect the result.
- Resolution The smallest change that a measuring instrument can show.
- Parallax error A systematic error caused by reading a scale from an angle rather than at eye level.
Common Mistakes
- Recording the final length as the extension, instead of subtracting the original length.
- Reading the ruler from an angle, which causes a parallax error.
- Taking readings before the mass has stopped moving, which adds random error.
- Plotting the dependent variable on the horizontal axis without stating that the axes have been chosen this way.
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