======Electromagnetic Survey With Magnets and Compass====== **Materials: **{{$demo.materials_description}}\\ **Difficulty: **{{$demo.difficulty_description}}\\ **Safety: **{{$demo.safety_description}}\\ \\ **Categories:** {{$demo.categories}} \\ **Alternative titles:** Magnetic Prospecting, Compass Deflection Ore Model ====Summary==== {{$demo.summary}} ====Procedure==== - Fill a tray about 3-4 cm deep with dry sand. - Bury several small magnets beneath the surface at different depths and positions. Keep their locations hidden from observers. - Smooth the sand surface so no magnet positions are visible. - “Fly” the compass slowly over the sand surface, following straight survey lines across the tray (like an aerial survey). - Observe and record any deflection of the compass needle as it passes over certain areas. - Mark these positions on a simple grid map to represent zones of magnetic anomaly. - Once the survey is complete, uncover the magnets and compare the detected positions to the actual buried locations. ====Links==== *None available. ====Variations==== * Use magnets of different strengths to simulate ore bodies of varying sizes. * Bury magnets at different depths and compare the magnitude of compass deflection. * Create a contour map of magnetic field strength using multiple compass readings. ====Safety Precautions==== * Handle strong magnets carefully to avoid pinching fingers or damaging electronics. * Keep magnets away from computers, credit cards, and magnetic storage devices. * Do not use loose iron filings — they can stick to magnets. ====Questions to Consider==== * How does the compass needle behave near a magnet compared to the background field? * Why do magnetic surveys help locate buried ore bodies? * How would the strength and depth of a real ore body affect the magnetic anomaly measured? * What other geophysical survey methods (e.g., electrical, seismic) can detect underground structures? * How is this model similar to and different from real airborne magnetic surveys?