2. Magnification Upon completion of the topic of Magnification, you will be able to: Calculate the magnification of an object Describe how a converging lens is used in a magnifying glass.

3. Calculating Magnification

4. Worked Example If the magnification is 1, the image is the same height as the object. If the magnification is less than one then the image is smaller than the object. If light from an object of height 40 cm passes through a lens with magnification 0.5, what height is the image? 0.5 = x/0.4 X=(0.5)(0.4) = 0.2 m = 20 cm.

5. Basic Questions An image 2 cm high is focussed onto a film. The object is 10 cm high. Calculate magnification. Light from a 2 cm high object produces an image 56 cm high. Calculate magnification. An image 4.8 cm high is focussed on a CCD by a lens. The object being photographed is 19.2 cm tall. Calculate the magnification.

6. A magnifying glass uses a single converging lens to magnify an object. For the lens to act as a magnifying glass, the object must be close to the lens. It needs to be nearer to the lens than the principal focus ( distance from lens must be less than the focal length) The image produced by the magnifying glass is on the same side as the object. Magnified, Upright, Virtual image which is further away from the lens.

7. The Human Eye You should be able to Describe the Structure of the Human Eye, and state the functions of each part of the eye. State the range of vision of the human eye.

8. The Human Eye: Main Parts The eye contains a ________. This is held in place by __________ ________. It is unlike most others in that it can change ________. Once light passes through this, it is _________ and focussed onto the back of the eye onto a layer called the ____________. This detects the light, and sends a signal to the brain through the _________ ________. lens suspensoryligaments shape refracted retina optic nerve DON’T TAKE DOWN

9. The Human Eye: Other Parts The eye needs to be protected from two things! Physical Damage Too much light which would desensitise the retina. - The cornea is a hard, transparent layer. - The Iris is the coloured part of the eye. It controls how much light enters the eye through the pupil. - The pupil is the gap in the centre of the iris. DON’T TAKE DOWN

10. Complete the table PartFunction Iris Pupil Lens Retina Optic Nerve Cornea Suspensory Ligaments Only one sentence is needed! Factual & Concise

11. Changing Focus As the lens is able to change the shape of its lens, the focal point can change. This occurs due to the ciliary muscles, which can contract and expand. When they contract, the lens is stretched, and far away objects can be seen. When they expand, the lens is compressed, and we can see nearby objects.

12. The range of vision The range of vision describes the distance from the nearest point of to the furthest point that the eye can focus on. The range of human vision is 25 cm to infinity The eye can see objects so far away as the light from these is travelling parallel to the principal axis.

13. AQA Questions How does the lens change shape? Mention the two kep parts in your answer. Suggest a reason as to why it becomes difficult for the eye to focus on nearby objects.

14. Problems with Eyesight After studying this topic, you should be able to Understand what is meant by Long- and short- sightedness. Know the reasons for each condition. Describe how corrective lenses can be used.

15. What causes problems with eye- sight?? The lens The cornea The overall shape of the eye Lazy ligaments Crazy Ciliarys Each of these can result in light not being focussed on the retina.

16. Long-Sightedness The eye can not focus on objects that are close to the eye. 1. Eye may be too short 2. May not be able to make the lens fat enough to focus the light. 3. Often happens as people get older, as the lens loses elasticity. Get me my reading glasses!!

17. Short Sightedness Cant focus on objects that are far away. 1. Eye may be slightly long 2. Can’t make the lens thin enough to focus the light on the retina. People naturally squint to try and see things far away.

18. Using Glasses Corrective Lenses are used to help form a clear image. These refract the light passing through them so as to form a clear image on the retina.

19. Correcting Long-Sightedness Yay…. A convex lens is used. Converges light from nearby objects onto the retina. This would be used in reading glasses. Hypermetropia is the medical term for longsightedness.

20. Correcting Short Sightedness We use a diverging lens to correct this. Allows the light to be focussed on the retina instead of in front of it. Myopia is the medical term for short- sightedness.