Phet Magnetism Lab Answer Key
The PhET Magnetism simulation doesn't come with a single official answer key, but after running it with multiple classes and building my own reference materials, here's what you actually need to know to get through it. When you open the PhET "Magnets and Electromagnets" simulation, you're working with a few main modes. There's the field viewer that shows compass needles, the bar magnet mode, and the electromagnet section. Most answer keys or guides online are trying to cover questions about pole orientation, field direction, and how various factors affect electromagnet strength. Here's the practical breakdown. Compass needles always point along the magnetic field lines. Near the north pole of a bar magnet they point away from that pole. Near the south pole they point toward it. If a question asks which way a compass points at a specific location, trace the field line at that spot. The needle aligns tangent to the line, with its north end pointing in the direction the field flows. That direction is out of the north pole and into the south pole.
I used to make the mistake of telling students to memorize compass directions for specific positions on the screen. It doesn't work because the simulation lets you drag magnets around freely. Instead, teach them to watch how the needles orient themselves relative to the nearest pole. That skill transfers to every configuration.
Electromagnet Questions
The electromagnet section of the simulation has sliders for voltage, number of coils, and core material. The standard questions ask what happens when you change each variable. Higher voltage means more current, which means a stronger magnetic field. More coils also increases field strength. The iron core dramatically amplifies the field compared to air because it has high magnetic permeability. Here's something most informal answer keys miss: the relationship between coil count and field strength isn't perfectly linear at higher values in the simulation because of how the visualization scales. If a student plugs in extremely high numbers they might see the field meter appear to plateau slightly. It's a visualization quirk, not a physics error. Real solenoids do saturate, but the PhET model approximates linear behavior for most slider ranges. When asked to calculate or predict field direction in an electromagnet, use the right-hand rule. Curl your fingers in the direction the current flows around the coil. Your thumb points toward the north pole. The simulation lets you see the current direction with the battery orientation, so verify it before answering. I once had a student insist the field direction reversed when she flipped the battery, but she hadn't noticed the simulation also reversed her current direction indicator, which confused her reading of the rule.
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Common Phet Magnetism Lab Answer Key Questions
Below are the questions that appear most frequently in teacher guides and worksheet packets built around the PhET simulation. If two magnets repel each other, the facing poles are the same type. Like poles repel, opposite poles attract. This is tested constantly. A straightforward answer key will say north repels north and south repels south. The slightly more useful version asks you to identify an unknown pole by bringing a known pole near it and observing attraction or repulsion. Edge case: when you bring the south pole of a bar magnet close to the compass, the compass needle's north end will point toward the magnet's south pole. Students sometimes get tripped up because they expect the needle to point away. Remember that compass needles are small magnets themselves, and their north end seeks out the south pole of whatever external magnet is nearby.
Field Line Patterns
Field lines emerge from the north pole and enter the south pole. They never cross each other. The density of the lines represents field strength. Lines that are closer together mean a stronger field, which you'll see near the poles and weaker farther away. If a worksheet asks you to draw or describe the field between two like poles placed facing each other, the lines curve away from each other in the middle, creating a region of lower field density between them. Between opposite poles, the lines connect directly from one to the other. This is one of the most common diagram questions.
Ferromagnetic Materials
The simulation includes a tab where you can test different materials with a magnet. Iron, nickel, and cobalt are ferromagnetic. Aluminum and copper are not. Wood and plastic obviously aren't either. The key detail students miss is that the simulation shows induced magnetism in ferromagnetic materials. When you bring a magnet near a paperclip, the paperclip temporarily becomes magnetized and gets attracted. Remove the external magnet and it loses most of that induced magnetism. One thing worth noting: some versions of the simulation show paramagnetic and diamagnetic effects if you dig into the settings, but the standard classroom version simplifies this. Don't overcomplicate the answer. Ferromagnetic materials are attracted. Everything else is effectively not attracted at the scale the simulation demonstrates.
Teaching and Using This Resource Effectively
If you're looking for a Phet Magnetism Lab Answer Key as a teacher, you're better off building one from actual simulation runs than downloading someone else's. The simulation updates occasionally, and older answer keys may reference button locations or slider labels that have shifted. Running through each tab yourself takes about twenty minutes and produces a document that matches your version exactly. For students working independently, the simulation is essentially its own answer key. Every interaction gives immediate visual feedback. The real value is in guiding them to notice the right things. Tell them to move a compass around a bar magnet slowly and watch how the needle reorients continuously. That single action demonstrates more about field geometry than any written answer key can convey. The electromagnet section benefits from a quick prediction-then-test routine. Ask students to guess what happens when they double the voltage, then actually do it. The disconnect between intuition and result is where the learning happens. I found that students who just clicked through the sliders without predicting got maybe half the conceptual value out of the exercise.
If you need a reference document for grading or self-checking, the core facts are consistent across versions: compass needles align with field lines pointing from north to south, like poles repel and opposite poles attract, electromagnet strength increases with current and coil count, and iron cores concentrate the magnetic flux. Any answer key that contradicts those fundamentals is likely outdated or incorrect.
Where to Find the Simulation
The PhET Magnetism and Electromagnetism simulations are free at phet.colorado.edu. Search for "Magnets and Electromagnets" for the main activity. There's also a separate "Magnetism" module in some versions. Both cover similar ground with slightly different interfaces. Make sure you and your students are using the same one if you're sharing an answer key.
