A Text-Book of Physics Volume 2

A Text-Book of Physics Volume 2

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1912 edition. Excerpt: ...does. We can thus construct the direction of PR geometrically. In Fig. 31a we see that PR cuts CA in F, and in Fig. 316 PR proceeds as though from a point F in CA. Since QP is parallel to CA.-. i = PCF in both figures, and in Fig. 316 r = vertically opposite angle CPF, .-.in both figures %_= PCF = V = CPF, .-. in the triangle CFP-. side FC = side FP. Now so long as P is near to A the lengths FP and FA will be very nearly equal, .'. FC is very nearly equal to FA, or F is very nearly the middle point of CA. Whence we may conclude that all rays parallel to CA proceed, after reflection, either to or from a point nearly half-way between C and A. Now the rays from a very distant object such as the sun are practically parallel; consequently the image of a very distant object will lie half-way between C and A. The point where the image of a very distant object is formed by reflection in a mirror is called the Principal Focus, and the distance of this point from the mirror is called the Focal Distance or Focal Length of the mirror. Hence we have the rule that the principal focus of a mirror lies half-way between the centre of curvature and the surface of the mirror; or, the focal length of a mirror is equal to half its radius of curvature. We may express this thus in symbols: --In the case of Fig. 31a. In the case of Fig. 31&. V or/ = in both cases. 25.--Suppose that an object 00' (Fig. 32) is placed in front of a curved mirror. We know that a ray starting from 0' and passing through C, or going as though to or from C, is normal to the mirror, and is therefore reflected back along its former course. The image of 0' must therefore lie somewhere along O'C or O'C produced. We know also that such a ray as O'P, parallel to CA, will, after reflection, ...show more

Product details

  • Paperback | 46 pages
  • 189 x 246 x 3mm | 100g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236561562
  • 9781236561565