AP1200_Ch4_Optics-2008

AP1200_Ch4_Optics-2008 - AP1200 Foundation Physics Limited...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
AP1200 Foundation Physics Limited wisdom and incorrect predictions: "Everything that can be invented has been invented." -- Charles H. Duell, Commissioner, U.S. Office of Patents, 1899. Chapter 4: Optics The properties of light have been of interest for many centuries: z The ancient Greeks believed light was made up of particles. z Newton explained reflection and refraction using this particle description of light. z In 1678, Huygens explained many other properties of light by proposing light to be a wave. z In 1801, Young observed interference using double slits giving strong support to the wave theory of light. z In 1865, Maxwell developed the theory that electromagnetic waves travel at the speed of light. The wave theory of light seemed to be firmly established. z In 1900, Planck needed to use a particle theory of light to explain black body radiation. z Einstein, 1905, then used the particle model to explain the photoelectric effect. Today, we accept that light has a dual character, called particle-wave duality: light exhibits properties of both waves and particles. In this chapter, we will consider only a simple model of light: light as rays. This model is used in geometric optics . 4.1 Measuring the Speed of Light The earliest estimates for the speed of light were based on astronomical measurements. The first successful laboratory experiment was made by Fizeau (Fig. 4.1). Light was passed through a toothed wheel and reflected off a mirror. As the wheel is sped up, the forward beam may pass through slot A, but the reflected beam may be blocked by tooth B. Speeding up the wheel further allows the reflected beam to pass though slot C. Knowing the number of slots and the rate of rotation of wheel allows the speed of light to be measured. Fizeau obtained 3.1 × 10 8 m/s. Today the accepted value is: 8 10 9979 . 2 × = c m/s
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Fig. 4.1 Fizeau’s Experiment 4.2 The Ray Approximation in Geometric Optics In geometric optics, it is assumed that light travels in a straight line as it passes through a uniform medium. Light changes direction only if the optical properties of the medium change. We use the ray approximation, which states that rays are straight lines perpendicular to the wave fronts (Fig. 4.2). Fig. 4.2 Light Rays
Background image of page 2
If a wave meets a barrier in which there is a small circular whole of diameter d (Fig. 4.3), then z if d >> λ , the emerging wave continues in a straight line z if d ~ , the emerging wave will spread out – diffusion due to diffraction z if d << , the emerging wave will spread more such that the hole approximates to a point source (Huygens’ Principle). This implies that the ray approximation is only valid for wavelengths that are small compared to the size of the objects in the path of the light. Fig. 4.3
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 19

AP1200_Ch4_Optics-2008 - AP1200 Foundation Physics Limited...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online