Reflections. I feel pretty, oh so pretty

Transcription

1 Reflections I feel pretty, oh so pretty

2 Objectives By the end of the lesson, you should be able to: Draw an accurate reflective angle Determine the focal length of a spherical mirror

3 Light Review Light travels in straight lines through space Objects like a mirror can change the path of light A new straight line is created by reflecting off a polished surface (mirror)

4 Light & Rays What is a ray? A line which start at a point (the tail) and travels in a straight line from that point. An arrow (the head) is used to represent the direction of travel Light is represented by using straight arrows called rays The study of light is called optics The study of light using rays is called ray optics

5 Reflection When light rays strike a surface they bounce off This process is called reflection Surface

6 Angle of Reflection A light ray reflects from the surface of an object at the same angle at which is strikes the object. Angles are measured from the normal line which is a line perpendicular to the surface. Normal θ θ Surface

7 Reflection The angle of incidence is always equal to the angle of reflection This is called the Law of Reflection The incident ray, the normal line, and the reflected ray all lie in the same plane and this plane is called the plane of incidence They are said to be co planar

8 Angle of Reflection vs. Angle of Incidence The Angle of Incidence is the angle between the incoming light ray and the normal line Incoming ray is the Incident Ray The Angle of Reflection is the angle between the outgoing light ray and the normal line Outgoing ray is the Reflected Ray

9 Angle of Reflection vs. Angle of Incidence Which angle is which? Angle of Incidence θ Angle of Reflection θ Surface

10 Law of Reflection θ θ

11 Reflection vs. Diffuse Reflection Diffuse Reflection: The reflection of light off a rough surface such that the incident angle reflects at many different angles How can this be if the Law of Reflection must hold true? You can t break the laws of physics

12 Reflection vs. Diffuse Reflection The light is still obeying the Law of Reflection, however, the surface and normal lines are different at each point

13 Reflection & Mirrors Highly polished surfaces used to reflect light are called mirrors To be considered a mirror, the surface must reflect most (>80%) of light striking the surface Diffuse Reflection surfaces reflect much less than 80% of light Mirror surfaces can be made of aluminum and silver These reflect about 90% of the light that strikes them Most common mirrors are made by putting a thin metal coating on glass

14 Reflection & Mirrors If the metal coating is on the first surface that the light hits, the mirror is a first surface mirror Common household mirrors have the glass in front of the metal coating for protection. This is called a second surface mirror.

15 Types of Mirrors Mirrors with flat surfaces are called plane mirrors Mirrors with spherical reflecting surfaces are called spherical mirrors

16 Spherical Mirrors: Convex Spherical mirrors can be convex Convex mirrors provide wide angle views for security but also make objects appear further away

17 Spherical Mirrors: Concave Spherical mirrors can be concave Think of concave as being gouged in like a cave

18 Spherical Mirrors Concave Mirrors: Concave mirrors reflect light off the mirror s surface to a common point, or focal point, in front of the mirror.

19 Focal Point A focal point is where the reflected rays all meet The image is formed here Reflected light off a concave surface all meet at a focal point in front of the mirror Reflected light off a convex mirror all meet at a focal point behind the mirror

20 Focal Point Focal point

21 Focal Point Focal point

22 Focal Length Imagine a spherical (curved) mirror is made of many small lengths of planar mirrors Each length has normal line Each normal line is a radius of curvature To find the focal length use this equation Focal length = ½ radius of curvature f = ½ r

23 Refraction Do not try to bend the spoon, that is impossible. Only realize the truth: there is no spoon. Then you will see that it is not the spoon that bends, it is only yourself.

24 Refraction Bending of a wave as it changes speeds due to changing the density of the medium How do we use refraction to benefit our daily lives?

25 Refraction As a wave travels, it can pass through different media Media is the plural of medium

26 Refraction Bending Rules: 1. If the wave passes from a less dense to a more dense medium, the wave will bend toward the normal 2. If the wave passes from a more dense to a less dense medium, it will bend away from the normal

27 Refraction

28 Refraction

29 Refraction

30 Refraction & Prisms White light is the combination of all colors of light When light passes through a prism, does the density of the medium change?

31 Refraction & Prisms Due to the different wavelengths of each color of light, the amount each color is bent as it enters the prism varies

32 Refraction & Prisms

33 Refraction & Lenses A lens is a transparent object that refracts light rays in such a way that they converge or diverge to create an image Converging lenses are thicker in the middle than at the edges Diverging lenses are thicker at the edges than in the middle

34 Refraction & Lenses Focal Point: Just like with spherical mirrors, lenses have focal points, but lenses tend to have focal points on either side of the lens

35 Refraction & Lenses