PSC20 - Properties of Waves 3 The speed of light is in a vacuum. it travels 299 972 458 m/s. (rounded to m/s). Speed of light is given the symbol comes from the word meaning. How far do you think light would travel in exactly minute? If the circumference of the Earth is km, how many times will light travel around it in that minute? (very hypothetical as light travels in a straight line!) What is the wavelength of light that has a frequency of Hz? What colour is this light? As light passes through transparent substances, it due to interaction with the atoms. It actually is as it is repeatedly by the atoms, effectively slowing it down. This is quantified using the. n = Index of c = Speed of light in a ( ) v = the speed of light in the Note: The higher the Index, the the speed.
The speed of light in water is m/s. Find its Index of Refraction. The Index for Ethanol is. Find the speed of light in Ethanol. Refraction and Snell s Law As a light ray passes between of different optical densities (different speeds of light), the rays change direction due to. when a ray passes from, some of the light is reflected while some is refracted. This is called partial and partial. Light bends the normal if traveling into something more (air to glass) Light bends from the normal if traveling into something dense (glass to air) If the angle of incidence is, there is no. Principle of Reversibility of Light - if a light ray is, it travels back along the same. The angle the ray refracts to can be calculated using: Where: n = the index of refraction in medium 1 or 2. θ = the angle of the ray in medium 1 or 2. ***All angles are measured from the normal!***
A light beam in air (n= ) strikes the surface of a pond at an angle of. Find the angle the ray refracts to inside the water (n= ). A ray of light travels from water (n= ) into an unknown substance. If the angle of incidence is and the angle of refraction is, what is the index of refraction? What is the substance? A ray of light is travels from ethyl alcohol into an unknown substance where the speed of light is m/s. If the angle in the unknown substance is, what was the angle of incidence? Total Internal Reflection Critical Angle When the speed of light (glass to air) light is to a greater extent than in the cases where speed. As the angle of incidence, reflected rays become more. The angle of also increases to a maximum of. After this point, all light is. This point is called. This can only occur when light is up. (ie. going into a medium that is ).
Critical Angle - when the angle of refraction is. When calculating the critical angle, set the refractive angle to. What is the critical angle for light traveling from crown glass into air? What is the critical angle for light traveling from diamond into water? Lenses There are 2 types 1) (Convex) in the middle Bring light rays together 2) (Concave) in the middle cause light rays to spread apart
Images in Lenses (O) geometric center. - From the center of the lens to the principle axis (P.A.) straight line perpendicular to the lens. (F) the point at which light rays are refracted through (l) distance between O and F. - Measured along the principle axis. Rules for Rays in a Converging Lens 1. A ray parallel to the P.A. is through the. 2. A ray that passes through the principal focus (F ) is refracted to the P.A. 3. A ray that passes through the (O) goes straight through (no bending). h o = cm d o = cm f = cm h o = cm d o = cm f = cm
h i = cm d i = cm f = cm Images Formed in Diverging Lenses Parallel rays are The principle focus in a converging lens is, where in a diverging lens it is. All images are ALWAYS,, and. Rules for Rays in Diverging Lenses 1. A ray parallel to the P.A. is refracted to pass through F. 2. A ray that passes through F is refracted parallel to the P.A. 3. A ray that passes through O goes straight through. h o = cm d o = cm f = cm
h o = cm d o = cm f = cm Thin Lens Equation ***This is the same as the MIRROR EQUATION Sign Conventions All distances are measured from the. Distances of real images are. Distances of virtual images are. Object and image heights are when measured upwards from the P.A. It is for any inverted image. Magnification Equation An object cm high is cm from a converging lens having a focal length of cm. How far from the image is the lens and how tall is it?
A diverging lens has a focal length of cm. If an image is found cm from the lens, how far from the lens is the object? If the image is m tall, what is the height of the object? What is the magnification? The Human Eye Cornea covering of the eye found in front of the pupil. helps to the image. Lens and. Converges light and focuses images to the back of the. Lens is thin in the middle when the muscles are. Lens is in the middle when muscles. This muscle adjustment is called. Retina a thin layer of nerve cells that line the back of the eye. consist of and are more numerous and do not detect color. detect color. Color Blindness caused by lack of development of. Blind Spot Is the junction between the and. There are no light sensitive cells in this area. Vitreous Humour part of the eye.
Ciliary Muscles they contract and relax in order to change the. This changes the of your lens and allows us to focus. Aqueous Humour Liquid between the and the. Sclerotic tough outer. Optic Nerve is the junction between the and the. It sends electrical signals to the brain. The image is actually on the retina but the straightens it out for you. Iris (Diaphram) located at the of the eye. Pupil the in the center of the eye. The size of the hole is controlled by the. Farsightedness (hypermetropia / hypermyopia) Is a defect in the eye resulting in the inability to see objects clearly. Usually occurs because the distance between the lens and the retina is. Can also occur if the cornea and the lens is too the image on the retina. Can be corrected by a lens. Nearsightedness (myopia) Is an inability to see objects clearly. The distance between the lens and the retina is too or the lens-cornea combination is. This means the parallel light rays focus in of the retina. Can be corrected with a lens. Astigmatism If the is curved more in one way than the other. This causes a image. Corrected with lenses that have more where the eye has less and vice-versa.