Brightness, Speed, and Evidence

Overview

In this 40-minute investigation, students test how voltage, current, and resistance affect LED brightness and motor speed in controlled 9V circuits. They organize observations and measurements, compare predictions with evidence, and revise circuit diagrams or explanations when the data does not support their original thinking.

Learning intentions

• Students will be able to predict how changing voltage, current, or resistance may affect an LED and motor.
• Students will be able to conduct a controlled circuit test and record results in a table.
• Students will be able to use evidence to explain patterns in brightness and motor speed.
• Students will be able to revise a circuit diagram or claim when observations show it is inaccurate.

Success criteria

• I can identify the variable being changed and the variables being kept the same.
• I can record voltage, current, brightness, and motor-speed observations clearly.
• I can compare my prediction with my results using specific evidence.
• I can revise an explanation or diagram and explain why the change is needed.

Curriculum links

• Washington State science learning: planning and carrying out controlled investigations, analyzing data, and using evidence to support explanations about electric circuits.
• Ratios and proportional relationships: describe relationships between changing electrical quantities and observed effects.
• Reading in Science and Technical Subjects: follow a procedure, interpret circuit data, and identify evidence supporting a conclusion.
• Writing in Science and Technical Subjects: write a concise evidence-based claim, including reasoning from observations and measurements.

Lesson structure (40 minutes)

1. 0–5 min · Hook and prediction. Open with the hook and prediction slide showing two identical LEDs or motors with a striking “Which will be brighter or faster?” comparison. Ask: “If the voltage stays at 9V, what might happen when resistance increases?” Students make a prediction and briefly justify it in their notebooks.

2. 5–10 min · Safety and investigation briefing. Use the safety and test-plan slides to review battery polarity, LED polarity, short circuits, warm components, and the rule that students change only one variable at a time. Demonstrate a baseline circuit with a 9V battery, resistor, LED, and switch; students identify the independent variable, dependent variable, and controls on the circuit investigation worksheet.

3. 10–24 min · Controlled circuit tests. Place students in five groups of five, assigning roles: builder, voltage reader, current reader, observer, and recorder. Each group tests a baseline circuit and then one controlled change, such as a different resistance value or a different number of components in series, while keeping the battery, component type, connection arrangement, and test time consistent. Students use the worksheet to record at least two trials, voltage and current readings when available, LED brightness on a 1–5 scale, and motor speed on a 1–5 scale. Circulate and ask, “What exactly changed?” and “What evidence would make your comparison fair?”

4. 24–30 min · Organize and interpret results. Display the results-table and discussion slides and ask groups to check units, labels, repeated trials, and whether their comparison is fair. Students calculate or describe the change between conditions, then write one pattern beginning, “When ___ increased/decreased, ___ because our evidence shows ___.” Groups compare results with another group that tested a different condition.

5. 30–36 min · Revise using evidence. Show two intentionally flawed circuit diagrams or explanations on the error-analysis slides—for example, an LED connected without a resistor or a claim that “more resistance always makes a motor faster.” Students select one and revise it on the worksheet, labeling the corrected circuit or rewriting the claim. They must cite one specific observation or measurement as evidence.

6. 36–40 min · Share and exit assessment. Invite two groups to share a result and a revision. Finish with the claim-evidence-reasoning exit prompt: “How did changing resistance affect the LED or motor in your test? State a claim, include one piece of data or observation, and explain why it supports your claim.” Collect worksheets as students leave.

Resources

• Five 9V battery holders or battery packs
• LEDs, resistors with several values, small low-voltage motors, switches, wires, and alligator clips
• Five digital multimeters or teacher-operated meters
• Safety glasses and component trays
• the Brightness, Speed, and Evidence slide deck
• the circuit investigation worksheet
• Five rulers or simple visual references for consistent motor-speed observation, if available

Assessment

• During testing, check whether students identify the changed variable and maintain controls; prompt groups that alter more than one condition.
• Review tables for labeled variables, units, repeated trials, and observations that match the tested setup.
• Use the exit response to assess whether students make a supported claim, refer to evidence, and explain a relationship between circuit conditions and component behavior.

Differentiation

• Provide a partially completed results table, a variable word bank, and sentence frames such as “Our data shows…” and “This supports our claim because…” for students needing support.
• Pair students strategically and assign concrete roles; allow students to report brightness and speed with the 1–5 scale before adding numerical comparisons.
• For EAL students, display visuals and gestures for voltage, current, resistance, brighter, dimmer, faster, and slower; accept labeled diagrams plus oral explanation before written revision.
• Challenge ready students to explain why a resistor protects an LED, compare the usefulness of current and voltage data, or identify a limitation in their investigation, such as subjective speed ratings or inconsistent connections.