Lenses and Images

Different Images Produce Different Kinds of ImagesLenses form images by refracting light and changing its direction. There are two main types of lenses converging and diverging. They have different shapes and have opposite effects on the light rays. 1. A converging lens is convex - it bulges outwards. It causes parallel rays of light to converge (move together) at the principal focus 2. A diverging lens is concave - it caves inwards.It causes the parallel rays of light to diverge (spread out)3. The axis of the lens a line passing through the middle of the lens 4. The principal focus of a converging lens is where rays hitting the lens parallel to the axis meet 4. The principal focus of a diverging lens is the point where the rays hitting the lens parallel to the axis appear to all come from - you can trace them back until they appear to meet up at the point behind the lens.There are THREE Rules for Refraction in CONVERGING Lenses...An incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side An incident ray passing through the principal focus refracts through the lens and travels parallel to the axis An incident ray passing through the centre of the lens carries in the same direction   There are THREE Rules for Refraction in DIVERGING Lenses... An incident ray parallel to the axis refracts through the lens and travels in line with the principal focus (so it appears to come from a principal focus) An incident ray passing through the lens towards the principal focus refracts through the lens and travels parallel to the axis An incident ray passing through the centre of the lens carries on in the same direction Lenses can Produce Real or Virtual Images1. A real image is where the light from an object comes together to form an image on a 'screen' - like the image formed on an eye's retina (the screen on the back of the eye)2. A virtual image is when the rays are diverging, so the light from the object appears to be coming from a completely different place You can get a virtual image from a magnifying glass - the image looks bigger than the object actually isTo describe an image properly, you need to say three things: How big it is compared to the object Whether it is upright of inverted relative to the object Whether it's real or virtual

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