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D2.2 · Investigate which materials hold or transfer electric charge

Learn to investigate which materials hold or transfer electric charge through clear examples and targeted practice.

Ontario Grade 9 Science

Physics: Principles and Applications of Electricity

A Grade 9 lesson on fair comparisons, observable effects, and careful conclusions

A plastic comb rubbed on dry hair may attract tiny pieces of paper. The pieces move even though the comb does not touch them. This everyday observation raises a science question: Do different materials hold or transfer electric charge differently? Charge itself is not visible in this kind of test. Instead, we look for an effect, such as a detector responding or a light object moving. A careful comparison can show how particular samples behaved under particular conditions. It cannot prove that every object made from a material always behaves the same way.

What you will learn

Explain what it means for a material to hold or transfer electric charge.
Plan a safe, fair comparison using teacher-approved materials and procedures.
Use repeated observations to make a limited conclusion and describe what the evidence cannot show.

From an everyday effect to a science question

Electric charge is a property of matter. Matter is the material that objects are made of. In this investigation, you do not need to see charge directly. You look for an effect that suggests charge is present, such as a detector responding.

A material that holds charge allows charge to remain in a region long enough for an effect to be detected. A material that transfers charge allows charge to move between places or objects. These descriptions help us ask questions, but the result can also depend on the sample’s condition and how it is tested.

A useful question is: When samples are treated in the same way, do they differ in how long a charge effect can be detected, or in whether they transfer charge during contact? A fair test is a comparison that changes the material being studied while keeping other important conditions as similar as possible.

Look for an observable effect rather than claiming to see charge directly.
Holding charge means an effect remains detectable for a time; transferring charge means charge moves between places or objects.
A fair comparison changes the material, not several test conditions at once.

Plan a safe and fair classroom inquiry

A model is a simplified way to describe something that is difficult to observe directly. Imagine charge as something that can move between objects or spread through a material. This model can help explain why a detector might respond differently for different samples. It is not a picture of charge that can be seen with the eyes, and it does not replace observations.

A teacher may provide clean, dry samples, a safe method for treating them, and a simple detector or light-object test. Follow the teacher’s directions and use only approved classroom equipment. Do not use wall outlets, mains electricity, batteries, flames, or chemical treatments for this investigation. Do not try the activity at home without a responsible teacher’s approval and suitable equipment.

Choose one main factor to compare: the material. Use samples of similar size where practical. Treat each sample with the same approved procedure. Keep the detector or test object, distance, waiting time, and contact method consistent. If the test involves touching two objects together, keep the contact time and area similar. These steps make it more likely that a difference in the result is linked to the material rather than to a different procedure.

Repeat trials and record what happened before explaining why. For example, “the detector responded in two trials” is an observation. “This sample held charge better” is an interpretation. The interpretation needs repeated comparisons and should be limited to the conditions tested. Handling, moisture, sample coatings, or uneven treatment can affect results.

Use teacher-approved equipment and procedures; do not improvise electrical or chemical tests.
Keep test conditions consistent and repeat comparisons.
Record observations first, then make a conclusion that fits them.

Use evidence without overstating it

Evidence is information gathered through observations or measurements. If a detector responds more often for one sample than another under the same conditions, that is evidence that the tested samples behaved differently in that test. It does not prove that every object made from the first material will always hold charge longer.

A simplified model helps organize or explain evidence, but the model is not the evidence. A detector response is an observation. Saying that charge remained on a sample is a model-based explanation of that observation. The test may not show exactly where charge moved or how much remained.

Every test has limits. A detector may fail to show a weak effect. Damp air, dirt, coatings, sample shape, or handling may change the result. If no response is detected, the careful statement is that no response was detected under those conditions. That is not proof that no charge remained.

Scientific evidence is different from a social or ethical judgment. Evidence can help answer how samples behaved in a test. It does not, by itself, decide whether a material is good, bad, or the best choice for a human purpose.

Distinguish an observation from an explanation based on a model.
Limit conclusions to the samples and conditions actually tested.
A detector’s lack of response does not prove that no charge remains.

Observation and conclusion

Observation	What it can support
The detector responded in two of three trials.	A detectable effect occurred in those trials.
One sample responded more often than another under the same procedure.	The tested samples behaved differently in that comparison.
The detector did not respond after a wait.	No effect was detected then; this does not prove that no charge remained.

Worked example

Compare repeated results

Hypothetical classroom scenario: A teacher-led test uses one plastic strip and one cloth strip. The strips are treated using the same approved procedure, and the same detector is used at the same distance. The detector responds to the plastic strip in three repeated trials and to the cloth strip in one of three trials. What can you conclude?

Identify the evidence
The evidence is the detector response in each repeated trial. The plastic sample produced a response in all three trials, while the cloth sample produced a response in one.
Make a limited comparison
Under this test procedure, the plastic sample showed a detectable charge effect more consistently than the cloth sample. This conclusion applies to these samples and these conditions.
State a limit
These hypothetical results do not prove that all plastic holds charge better than all cloth. Surface condition, handling, or other differences between samples could affect the outcome.

Answer: In this hypothetical test, the plastic sample showed a detectable charge effect more consistently. The evidence supports a comparison of the tested samples, not a universal rule about plastic and cloth.

Check: The conclusion matches the repeated observations and does not claim more than the test established.

Worked example

Spot an unfair comparison

A student rubs a metal spoon for a short time and a plastic ruler for a much longer time. The ruler affects a nearby paper piece, but the spoon does not. Is this enough to decide which material holds charge better?

Plan a fair material comparison

This is a planning model, not experimental evidence. It does not show or measure charge; spacing is schematic.

Find the extra difference
The samples were treated for different lengths of time. Because the procedure changed as well as the material, the test does not show which material caused the different result.
Improve the comparison
With teacher guidance, repeat the test using the same approved treatment procedure and time for each sample. Keep the paper piece and test distance the same too.
Compare repeated observations
Record several trials for each sample. A repeated difference under the same conditions gives better evidence than one unmatched trial.

Answer: No. Different treatment times make the comparison unfair. Repeat the test with the same procedure and conditions before drawing a conclusion about the materials.

Check: A fair comparison keeps important conditions similar so the material being tested is the main difference.

Worked example

Interpret an effect that fades

A treated sample affects a detector soon after a classroom test. After a short wait, the detector no longer responds. What does this tell you?

State what was observed
The detector responded soon after the test and did not respond after the wait. These are observations made at two different times.
Connect the observations to the question
The sample did not keep a detectable effect for the whole waiting period. Charge may have moved away, or the effect may have become too small for this detector to show.
Recognize what remains unknown
The test does not show exactly where charge went. It also does not prove that the sample can never hold charge. The detector and test conditions have limits.

Answer: A detectable effect was present at first but was not detected after the wait. This suggests that the sample did not maintain a detectable effect under those conditions; the test does not show exactly what happened to the charge.

Check: A missing response means no effect was detected in that test at that time. It does not prove that no charge remained.

Common mistakes and how to avoid them

Treating “holds charge” as meaning charge stays forever.

Correction: Describe how long an effect remained detectable and under which conditions.

Using one observation to claim that every object made from a material behaves the same way.

Correction: Limit the conclusion to the samples tested and repeat the comparison.

Changing the material and the procedure at the same time.

Correction: Keep the procedure consistent so the material is the main difference.

Treating a model as if it were directly observed.

Correction: The detector response is evidence; a model is a simplified way to explain it.

Lesson summary

Different samples may differ in how readily charge moves or how long a charge effect is detected.
A fair investigation uses a consistent procedure and repeated trials.
Evidence supports conclusions, but conclusions should stay within the limits of the test.
A model helps explain observations but does not replace them.

Check your understanding

Question 1

A student wants to compare two materials. Which plan gives the fairest test?

Use the same procedure, test distance, and detector for both materials.
Treat one material for longer so its effect is easier to see.
Use a different detector for each material.
Test one material once and the other several times.

Show answer and explanation

Use the same procedure, test distance, and detector for both materials.

Keeping the procedure, distance, and detector consistent makes the material the main difference in the comparison.

Question 2

A detector responds to one sample but not another in one trial. Which conclusion is best?

The first material always holds more charge.
The first tested sample produced a detectable effect in that trial, while the other did not.
The second sample contains no electric charge.
The detector proves exactly where charge moved.

Show answer and explanation

The first tested sample produced a detectable effect in that trial, while the other did not.

This conclusion describes what happened in one trial without claiming that the result applies to all samples or reveals exactly what happened to charge.

Key terms

Electric charge: A property of matter that can produce effects, such as a detector response.
Hold charge: Allow charge to remain in a region long enough for an effect to be detected.
Transfer charge: Allow charge to move from one place or object to another.
Evidence: Information gathered through observations or measurements.
Model: A simplified way to describe or explain something that is difficult to observe directly.
Fair test: A comparison that changes the factor being investigated while keeping other important conditions similar.

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About this lesson and its review

Published by DoAssignment. This reviewed lesson follows Ontario Grade 9 Science (SNC1W), expectation D2.2. It is a study resource, not an official curriculum publication.

Before publication, content is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability. Errors can still occur, so corrections are welcomed.

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