Sample Curriculum Unit: Series and Parallel Circuits

Unit overview and where it sits

Subject: high school physics or physical science. Length: ten lessons of roughly fifty minutes, so two standard weeks. Assumed prior knowledge: students can rearrange a simple equation and have met the idea of electric current informally. No prior circuit analysis is assumed.

Enduring understanding: how components are connected determines how current divides and how voltage drops, and that arrangement is a design choice with consequences you can predict before building anything.

Compelling question for the unit: why do the lights in your house stay on when one bulb burns out, when the old string of holiday lights all went dark together?

That question is doing real work. It is genuinely puzzling to a fifteen year old, it is answerable with exactly the physics in this unit, and it gives every lesson somewhere to point.

Learning objectives

Each objective names an observable action, the condition, and the standard. This is the list everything else in the unit is checked against, and any lesson or assessment item that does not serve one of these does not belong in the unit.

• 1. Given a circuit diagram, the student identifies each section as series or parallel and justifies the identification by reference to the number of current paths.
• 2. Given a series circuit with stated resistances and source voltage, the student calculates total resistance, current, and the voltage drop across each element, to within two percent.
• 3. Given a parallel circuit with stated resistances and source voltage, the student calculates total resistance, total current, and the current through each branch, to within two percent.
• 4. Given a combination circuit of at most two levels, the student reduces it stepwise to a single equivalent resistance and shows each reduction.
• 5. Given measured values from a physical circuit, the student compares measurement to prediction and accounts for the difference in terms of a named physical cause rather than the phrase human error.
• 6. Given a stated design requirement, the student chooses series or parallel, builds the circuit, and defends the choice using the behavior of current and voltage in each arrangement.

Assessment evidence, decided before the lessons

Backward design means this section is written before any lesson is planned. If we cannot name what would count as proof, we are not ready to teach it.

• Objective 1: a five item sorting check on circuit diagrams, with a written justification required on two of them.
• Objectives 2 and 3: a problem set with an answer key that lists the common wrong answers and the mental model producing each one.
• Objective 4: three combination circuit problems requiring the reduction steps to be shown, not just the final number.
• Objective 5: the lab write-up, specifically the discrepancy section.
• Objective 6: the summative design task described further down.

Lesson sequence

Ten lessons. The sequence is built so that measurement comes before calculation, because students who calculate first treat the lab as a check on their arithmetic rather than as a source of evidence.

• Lesson 1. The compelling question, and a demonstration: two bulb circuits, one series and one parallel, and one bulb removed from each. Students write a prediction before the removal and a revised explanation after. No formulas yet. This lesson exists to create the question the rest of the unit answers.
• Lesson 2. Current has paths. Students trace paths on diagrams and sort circuits by the number of paths. Objective 1 is taught here. Formative check A at the end.
• Lesson 3. Measurement before theory. Students build one series and one parallel circuit and measure current and voltage at several points, recording without explaining. The pattern is what matters, not the numbers.
• Lesson 4. Series relationships. Students derive from their own lesson 3 data that current is the same everywhere and voltage drops add. The equation is written on the board only after the class has stated the pattern.
• Lesson 5. Series calculation practice. Worked example, then near transfer, then varied surface stories. Objective 2. Formative check B.
• Lesson 6. Parallel relationships, following the same shape as lesson 4 using their own data: voltage is common, currents add, total resistance is less than the smallest branch.
• Lesson 7. Parallel calculation practice, including the reciprocal formula. Objective 3. Formative check C, which specifically targets the belief that resistances add in parallel.
• Lesson 8. Combination circuits. Stepwise reduction, taught explicitly as a procedure with the intermediate diagram redrawn at each step. Objective 4.
• Lesson 9. Lab: prediction, measurement, discrepancy. Full detail below. Objective 5.
• Lesson 10. Summative design task, and returning to the compelling question from lesson 1 with an answer students can now actually give. Objective 6.

The lab, designed against real constraints

This lab is specified the way we specify every lab, which means it is designed around what a school actually has rather than around ideal equipment.

Materials per group of three: one battery holder with two AA cells, four identical bulbs in holders or four resistors between 100 and 470 ohms, one multimeter, six alligator clip leads, one switch. If the school has no multimeters, the lab runs with bulb brightness as a qualitative proxy and the write-up shifts from numbers to ranked comparisons, which still serves objective 5.

Cost note: built from resistors rather than bulbs, a class set for ten groups is inexpensive and the components are reusable indefinitely. Bulbs are more intuitive for students and burn out, so we specify resistors for the calculation work and bulbs for the demonstrations.

Setup time: fifteen minutes to lay out trays before class, five minutes to collect at the end. The lab fits a fifty minute period only if the trays are pre-built, and the teacher guide says so plainly rather than leaving it to be discovered.

Procedure: students predict all values from their calculations first and write the predictions in ink, then build, then measure, then compare. Predicting first is the whole point and the sequence is enforced by the worksheet layout.

Expected results and realistic error: measured current typically runs five to fifteen percent below prediction with AA cells, because internal resistance and lead resistance are real and are not in the model. That gap is not a mistake, it is the lesson. Students who write human error in the discrepancy section have not met objective 5 and the rubric says so.

Fallback: if a group's circuit does not work, the troubleshooting sequence is check the switch, check each lead by continuity, check the battery voltage under load, then swap one component at a time. This sequence is printed on the student sheet, because a teacher with nine other groups cannot debug them one at a time.

Formative checks, and what each one detects

A formative check that only produces a score is a waste of the lesson time it consumes. Each of these is built to separate one specific wrong mental model from correct understanding.

• Check A, after lesson 2. Detects the belief that a circuit that looks visually branched on the page is parallel, regardless of whether the branches carry separate current paths. Distractors are drawn to look branched while being electrically series.
• Check B, after lesson 5. Detects current being consumed as it travels, meaning students expect less current after a resistor than before it. One item asks for current at two points in the same series loop, and any answer where they differ names the misconception exactly.
• Check C, after lesson 7. Detects resistances being added in parallel. Two resistors of 100 ohms in parallel: the answer 200 ohms means the reciprocal relationship has not landed, and the answer 50 ohms means it has. This one item is worth more diagnostically than a whole quiz.
• Each check takes under five minutes and is scored as a class tally, not individually. The teacher guide states the action threshold: if more than a third of the class holds the misconception, reteach before moving on, and the reteach sequence is written out.

Summative task

Students receive a design brief rather than an exam paper. Design and build a circuit for a model room with three lights, meeting these requirements: any one light can fail without the others going out, all three light at similar brightness, and one switch controls all three together.

They must submit a predicted circuit diagram with calculated values before building, the built circuit demonstrated working, measured values compared against prediction, and a written defense of the series and parallel choices they made in terms of current and voltage behavior.

This task requires objectives 1 through 6 in combination and cannot be completed by pattern matching to a worked example, which is the test of whether the unit taught what it claimed.

Rubric

Four criteria, four levels. The descriptions below are the level three, meeting expectations, anchor for each criterion. The full unit includes all four levels and two anchor examples per level.

• Circuit identification and reasoning. Meets: correctly identifies series and parallel sections in the design and justifies each by reference to current paths, not by visual appearance.
• Calculation. Meets: predicted values are correct to within two percent, and the working shows each reduction step rather than only the final result.
• Measurement and discrepancy. Meets: measurements are recorded with units and appropriate precision, and the difference from prediction is explained by a named physical cause such as internal resistance or lead resistance.
• Design defense. Meets: explains why the chosen arrangement satisfies each stated requirement, using the behavior of current and voltage, and identifies at least one arrangement that would fail a requirement and why.

Standards alignment

Mapped rather than asserted. This unit aligns to NGSS HS-PS3-3 in its design dimension, and carries the science and engineering practices of developing and using models, planning and carrying out investigations, and analyzing and interpreting data, with the crosscutting concepts of systems and system models, and energy and matter.

The practice dimension is designed into the tasks rather than added to the cover sheet. Students plan and carry out an investigation in lesson 9 and develop and use a model throughout, which is the part of three dimensional alignment that purchased curriculum most often only claims.

A full delivery includes the state standards map alongside the NGSS map, in a spreadsheet, so an administrator can check the claim rather than take it.

What a full delivery adds to this

This page is the unit's design and content. A delivered unit also includes the student-facing files, meaning the printable lab sheet, the problem sets with answer keys, and the slides, plus the full four level rubric with anchor examples, the standards map as a spreadsheet, and the teacher guide with pacing notes and reteach sequences.

Everything is delivered in editable formats and you own it. If this is the standard you want across a course or a whole program, the scope and process are on the curriculum development page.