Lenses and ray diagrams

• Lenses can focus and disperse light using refraction, with two main types: convex lenses refract parallel rays of light inwards to a single point called the principal focus, while concave lenses refract parallel rays outwards
• All lenses have a principal focus on both sides, equal distances from the center, and the principal focus always sits on the axis passing through the middle of the lens
• The distance between the principal focus and the center of the lens is the focal length, and the shorter the focal length, the more powerful the lens is in refracting light
• Real images are formed when light rays actually converge to form the image, like when light rays from different parts of an object converge through a lens to create an image on a screen
• When describing images in exams, mention if they are real or virtual, upright or inverted, and bigger or smaller than the object
• Concave or diverging lenses cause light rays to diverge and spread out
• When drawing a ray diagram for a concave lens, use a symbol with outwards pointing V shapes at either end to represent the lens getting wider towards the ends
• Add an axis, focal points on either side, and a dot labeled 2f on either side, twice as far away from the lens as the focal point
• In a ray diagram for a concave lens, incident rays are drawn coming out of the object, one parallel to the axis and another going towards the center of the lens
• The ray going through the center of the lens won't be refracted, while the other ray will be refracted towards the focal point
• To find the point where the rays cross and form the image, follow the refracted rays and find their intersection point
• The image formed by a concave lens is virtual, upright, and smaller than the object
• Convex or converging lenses focus light onto a single point
• If the object is between the focal point and the lens itself, the refracted rays won't meet, so the image is found by tracing them backwards using virtual rays