Tiêu đề 99 Waves and Optics.pdf ✅

MSTC 98: Waves and Optics 1. Waves Waves are a sustained disturbance of medium that can go from one place to another. Consider a rope held at two points. When one end of the rope is shaken, the resulting wave travels to the other end of the rope. Waves that travel in this style are called transverse waves since the vibrations occur perpendicular to the direction traveled. Consider a slinky held at two ends. When one end is pushed, a “wave” seems to form and travels to the other end. Waves that travel in this style are called longitudinal waves since the vibrations are in the same direction as they travel. An example of transverse waves is light waves. An example of longitudinal waves is sound waves. The amplitude of a wave is the maximum disturbance the waves cause in the medium. Crests are the tops of the waves. Troughs are the bottoms of the waves. The wavelength is the length between two consecutive crests (or two consecutive troughs). 2. Sound Waves The celerity of a wave is the speed at which it travels in a medium. For an object with bulk modulus K and density ρ, vs = √ K ρ The speed of sound in air at 0 °C is 331 m/s. The speed of sound is dependent on the temperature of the medium. The speed of sound increases by almost 0.61 m/s for every 1 °C increase in temperature. More accurately, for temperatures expressed in °C, vs = 331√1 + T°C 273. 15 The intensity of a sound wave is the power of that wave per unit time. The loudness (β) is a logarithmic scale of the intensity of the sound. β = 10 log I I0 The unit of loudness is the decibel (dB). Consider a moving source of sound with frequency fs . If it moves away from the observer, then the observed frequency is lower. If the source moves towards the observer, then the observed frequency is higher. f0 = fs ( crest speed relative to observer crest speed relative to source ) The relative speed of the wave crest to an observer moving at a speed of v0 towards the source is equal to v + v0. The relative speed of the wave crest to the source moving at a speed of vs towards the observer is equal to v −vs . f0 = fs ( v + v0 v − vs ) This change in frequency is called the Doppler effect.
3. Light 3.1.1. Reflection of Light Light hitting a plane surface is called the incident ray. Reflected rays are symmetric with the incident ray about a line normal to the surface. 3.1.2. Mirrors Plane mirrors form an image with the same height as the original image. The virtual image is also at the same distance from the mirror as the original image. For curved mirrors, the principal focus is the point to which all reflected light goes. Concave mirrors form inverted images and are beyond the principal focus. Convex mirrors form upright images in front of the principal focus. For curved mirrors, 1 d0 + 1 di = 2 R = 1 f where d0 and di are the distances of the object and the image, respectively, R is the radius of curvature of the mirror, and f is the focal distance. The size of an image is magnified by a factor magnification factor = | si s0 | Image Sources: Schaum’s Outlines: College Physics