{"product_id":"aragos-rotating-disc-plate-017-physics-poster","title":"Arago's Rotating Disc – Plate 017 Physics Poster","description":"\u003cp\u003ePlate 17 speaks for itself: \u003cem\u003e“Spin the copper and the needle follows, though copper isn't magnetic.”\u003c\/em\u003e\u003c\/p\u003e\u003ch3\u003eThe Physics\u003c\/h3\u003e\u003cp\u003eA spinning copper disc drags a magnetic needle hung above it. Copper is not ferromagnetic; motion through the needle's field drives eddy currents in the disc, and their field pulls the needle along.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eJ = σ (E + v × B)\u003c\/strong\u003e\u003c\/p\u003e\u003cul\u003e\n\u003cli\u003eJ: current density, A m⁻²\u003c\/li\u003e\n\u003cli\u003eσ: electrical conductivity, S m⁻¹\u003c\/li\u003e\n\u003cli\u003eE: electric field, V m⁻¹\u003c\/li\u003e\n\u003cli\u003ev: conductor velocity, m s⁻¹\u003c\/li\u003e\n\u003cli\u003eB: magnetic flux density, T\u003c\/li\u003e\n\u003c\/ul\u003e\u003cp\u003eEddy currents drag the needle. Arago, 1824. Faraday explains it, 1831.\u003c\/p\u003e\u003cp\u003e\u003cem\u003eHonest caveat:\u003c\/em\u003e Copper is weakly diamagnetic, but that is not what drives the effect.\u003c\/p\u003e\u003ch3\u003eSources\u003c\/h3\u003e\u003cul\u003e\u003cli\u003eM. Faraday, Phil. Trans. R. Soc. 122, 125 (1832).\u003c\/li\u003e\u003c\/ul\u003e\u003ch3\u003eOn the poster\u003c\/h3\u003e\u003cp\u003ePlate 017, “Arago's Rotating Disc”: the pixel-art plate with its slogan “Spin the copper and the needle follows, though copper isn't magnetic.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.\u003c\/p\u003e","brand":"Printify","offers":[{"title":"9'' x 12\" (Vertical) \/ Matte","offer_id":50961776083047,"sku":"29709477457904281467","price":19.99,"currency_code":"USD","in_stock":true},{"title":"9'' x 12\" (Vertical) \/ Fine Art","offer_id":50961776115815,"sku":"21144517803829792619","price":29.99,"currency_code":"USD","in_stock":true},{"title":"9'' x 12\" (Vertical) \/ Semi Glossy","offer_id":50961776148583,"sku":"14356346635627709131","price":19.99,"currency_code":"USD","in_stock":true},{"title":"18″ x 24″ (Vertical) \/ Fine Art","offer_id":50961776181351,"sku":"67851339446528583939","price":44.99,"currency_code":"USD","in_stock":true},{"title":"18″ x 24″ (Vertical) \/ Semi Glossy","offer_id":50961776214119,"sku":"23454805723292233205","price":29.99,"currency_code":"USD","in_stock":true},{"title":"18″ x 24″ (Vertical) \/ Matte","offer_id":50961776246887,"sku":"12730000276258388156","price":29.99,"currency_code":"USD","in_stock":true},{"title":"36'' x 48\" (Vertical) \/ Matte","offer_id":50961776279655,"sku":"84685913912978185628","price":69.99,"currency_code":"USD","in_stock":true},{"title":"36'' x 48\" (Vertical) \/ Fine Art","offer_id":50961776312423,"sku":"26014987520623631793","price":119.99,"currency_code":"USD","in_stock":true},{"title":"36'' x 48\" (Vertical) \/ Semi Glossy","offer_id":50961776345191,"sku":"15869839363140163074","price":69.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0596\/8746\/9159\/files\/7474024340863785901_2048.jpg?v=1793632568","url":"https:\/\/pixelatedphysics.com\/tr\/products\/aragos-rotating-disc-plate-017-physics-poster","provider":"Pixelated Physics","version":"1.0","type":"link"}