{"product_id":"mirrorspin-foucault-speed-of-light","title":"Mirrorspin – Foucault Speed of Light \/ 298 000 km\/s Physics Sticker","description":"\u003cp\u003eMirrorspin, a helmeted knight, aims a spinning mirror and a bright orange beam.\u003c\/p\u003e\u003ch3\u003eThe Physics\u003c\/h3\u003e\u003cp\u003eIn 1862 Léon Foucault measured the speed of light in a laboratory with a rapidly rotating mirror (Comptes rendus 55, 501). Light reflects off the spinning mirror to a distant fixed mirror and back. In the round-trip time the rotating mirror turns a tiny angle, so the returning spot lands slightly displaced. From the displacement, the path length and the spin rate he got c = 298 000 ± 500 km\/s, close to the modern value.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eΔα = 2ωD\/c\u003c\/strong\u003e\u003c\/p\u003e\u003cul\u003e\n\u003cli\u003eΔα: angle the mirror turns during the round trip (rad); the returning beam is deflected by 2Δα\u003c\/li\u003e\n\u003cli\u003eω: angular speed of the mirror (rad\/s)\u003c\/li\u003e\n\u003cli\u003eD: distance to the fixed mirror (m)\u003c\/li\u003e\n\u003cli\u003ec: speed of light (m\/s)\u003c\/li\u003e\n\u003c\/ul\u003e\u003cp\u003eIn 1850 the same method showed light is slower in water than in air, against the particle theory.\u003c\/p\u003e\u003cp\u003e\u003cem\u003eHonest caveat:\u003c\/em\u003e The formula is the simplest geometry; turning the spot displacement into an angle needs the lens distances of the real setup. The modern defined value is 299 792.458 km\/s. This is a different Foucault experiment from his pendulum.\u003c\/p\u003e\u003ch3\u003eOn the sticker\u003c\/h3\u003e\u003cp\u003eMirrorspin holds a round mirror with curved motion lines and a glowing orange beam running from it. Printed text: \u003cstrong\u003eMIRRORSPIN\u003c\/strong\u003e with the line \u003cstrong\u003e298 000 km\/s\u003c\/strong\u003e. Pixel-art kiss-cut vinyl sticker, white, in 2″, 3″, 4″ and 6″ sizes.\u003c\/p\u003e","brand":"Printify","offers":[{"title":"2\" × 2\" \/ White","offer_id":50964059062375,"sku":"23487338040611958561","price":4.99,"currency_code":"USD","in_stock":true},{"title":"3\" × 3\" \/ White","offer_id":50964059095143,"sku":"26037588462490189923","price":6.99,"currency_code":"USD","in_stock":true},{"title":"4\" × 4\" \/ White","offer_id":50964059127911,"sku":"17945016735736232834","price":8.99,"currency_code":"USD","in_stock":true},{"title":"6\" × 6\" \/ White","offer_id":50964059160679,"sku":"71027428081293263858","price":11.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0596\/8746\/9159\/files\/123621653549998021_1200.jpg?v=1793659013","url":"https:\/\/pixelatedphysics.com\/nl\/products\/mirrorspin-foucault-speed-of-light","provider":"Pixelated Physics","version":"1.0","type":"link"}