Bellringer What color would a basketball appear to be if under an orange flashlight? What color would it appear to be if under a red flashlight? Light Part II Concave Mirrors • Concave mirrors can form either virtual images, or real images. • A concave mirror is a mirror that curves inward like the inside of a bowl (think: cave-in). A concave mirror reflects light rays toward the center of the mirror. The light rays all meet at the same point, called a focal point. Concave Mirrors • • The image formed by a concave mirror is either a virtual image or a real image. This type of image depends on where the object is placed. A concave mirror forms a virtual image if the object is farther from the mirror than the focal point. (Remember, a virtual image is an upright image that seems to form behind the mirror.) Virtual Image from Concave Mirror Concave Mirrors • A concave mirror forms a real image if the object is farther from the mirror than the focal point. A real image forms when reflected light rays actually meet. A real image forms in front of the mirror. A real image is always upside down. Real Images from Concave Mirrors Convex Mirrors • Because the rays never meet, images formed by convex mirrors are always virtual and smaller than the object. • A convex mirror is a mirror with a surface that curves outward like the outside of a bowl. A convex mirror reflects light rays outward. The reflected rays spread out and never meet. However, the rays seem to be coming from a point beyond the mirror. The image looks as though it is behind the mirror. Convex Mirrors • Convex mirrors are used in cars as side mirrors. • “Objects in mirror are closer than they appear.” • Convex mirrors let you see a bigger area then other mirrors do. The compromise here is that it reduces the apparent size of the object being reflected. Refraction of Light • • • When light rays enter a medium at an angle, the change in speed causes the rays to bend, or change direction. Light travels at different speeds in different mediums. When light passes from air into water at an angle, one side of the light rays slows down before the other side. This causes the light to bend, or refract. Refraction of Light • How much a medium causes light to slow down and bend is the medium’s index of refraction. Air has an index of refraction of 1.00. Water has an index of refraction of 1.33. The higher the index of refraction, the more light slows down and bends. Refraction of Light • Remember, white light is made up of light of different wavelengths. When light enters a medium (prisms, water droplets, etc.) at an angle, longer wavelengths of light slow down and bend less than shorter wavelengths. The light separates into different colors. This is why sunlight may form a rainbow when it passes from air into raindrops. Lenses • • • An object’s position relative to the focal point determines whether a convex lens forms a real image or a virtual image. A concave lens can produce only virtual images because parallel light rays passing through the lens never meet. A lens is a curved piece of glass that is used to bend light. A lens forms a virtual image or a real image. The type of image depends on the shape of the lens and the position of the object. Lenses • A convex lens is thicker in the center than at the edges. A convex lens bends light rays toward the center of the lens. All the rays pass through the focal point. • The image formed with a convex lens can be a real image or a virtual image. If the object is farther from the lens than the focal point, a real image forms. If the object is closer to the lens than the focal point, a virtual image forms. Lenses • A concave lens is thinner in the center than at the edges. A concave lens bends light away from the center of the lens. The light rays never meet, so the image is always a virtual image. The image is upright and smaller than the object.