小型望远镜-ckw.PPT

GOT IT 懂嗎 ?. 31.3. You look through a lens at this page and see the words enlarged and right-side up. 你用一個透鏡來看這一頁，文字都放大而且正立。 Is the image you observe real or virtual? 你看到的像是實或虛？ Is the lens concave or convex? 透鏡是凹或凸？ Example 31.3. Fine Print 小字印刷 You ‘re using a magnifying glass (converging lens) with a 30-cm focal length to read a telephone book. 你用一個焦距為 30-cm 的放大鏡 (收斂透鏡 )來看電話簿。 How far from the page should you hold the lens in order to see the print enlarged three times? 如果要把字體放大三倍，透鏡應該離頁面多遠？ Image is upright enlarged so it must be virtual. 成像正立且放大，所以一定是虛的。 Hence 因此, h? 0, s? 0. 31.3. Refraction in Lenses: The Details鏡片內的折射：詳情 Refraction at a Curved Surface in the Paraxial Approximation 近軸假定下，彎曲表面的折射 Snell’s law: 史耐爾定律： ? paraxial approx. 近軸假定 Green line is tangent to lens surface at point A. 綠線與鏡面相切於 A 點。 It merges with segment AB in the paraxial approx. 在近軸假定下，它與 AB 弦融合。 T(BOC): T(BOA): T(BAC): T(BCI): T(IBA): Snell’s law: 史耐爾定律 Example 31.4. Cylindrical Aquarium 圓筒形魚缸 An aquarium consists of a thin-walled plastic tube 70 cm in diameter. 一個魚缸由一條直徑 70 cm 的薄壁塑料管組成。 For a cat looking directly into the aquarium, 對一頭直視魚缸的貓來說， what is the apparent distance to a fish 15 cm from the aquarium wall? 一條離魚缸壁 15 cm 的魚，看似有多遠？ Top view 下視圖 Plastic wall thin ? negligible. 塑料壁薄 ? 可忽略 nwater = 1.333 positive if 正號條件 s always 必然 s?, f, R same side of outgoing ray 與外出光線同一邊 h, h? above axis 在鏡軸之上 Lenses, Thick Thin 透鏡，厚和薄的 O1 ? I1 = O2 ? I2 LHS 左邊 (O1 ? I1 ) : RHS 右邊 (O2 ? I2 ) : Thin lens薄透鏡 (t ? 0) : Lensmaker’s formula 磨鏡人的公式 positive if 正號條件 s always 必然 s?, f, R same side of outgoing ray 與外出光線同一邊 h, h? above axis 在鏡軸之上 Common Lens Types 常見的透鏡形式 平-凸 双凸 新月凸面 平-凹 双凹 新月凹面 Example 31.5. Plano-Convex Lens 平-凸透鏡 Find an expression for the focal length of the plano-convex lens, given refractive index n and radius R for the curved surface. 已知折射率 n 和曲面半徑 R，求平-凸透鏡的焦距。 Object on left hand side: