# KS4 Light and Lenses

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# Light, The Eye & LensesLearning Objectives Candidates should use their skills, knowledge and understanding of how science works:

• to construct ray diagrams to show the formation of images by diverging lenses and converging lenses.

• to explain the use of a converging lens as a magnifying glass and in a camera.

• draw and interpret ray diagrams in order to determine the nature of the image.

• evaluate the use of different lenses for the correction of defects of vision.

• t o calculate the magnification produced by a lens or mirror using the formula:

magnification = image height ÷ object height

Their skills, knowledge and understanding of how science works should be set in these substantive contexts:

• Refraction is the change of direction of light as it passes from one medium to another.

• A lens forms an image by refracting light.

• In a convex or converging lens, parallel rays of light are brought to a focus at the principal focus.

• The distance from the lens to the principal focus is called the focal length.

• refractive index = sin i ÷ sin r

• The nature of an image is defined by its size relative to the object, whether it is upright or inverted relative to the object and whether it is real or virtual.

• The nature of the image produced by a converging lens for an object placed at different distances from the lens.

• The use of a converging lens as a magnifying glass.

• The nature of the image produced by a concave or diverging lens.

• The construction of ray diagrams to show the formation of images by converging and diverging lenses.

• The structure of the eye, limited to:

• retina

• lens

• cornea

• pupil /iris

• ciliary muscle

• suspensory ligaments

• Correction of vision using convex and concave lenses to produce an image on the retina:

• long sight, caused by the eyeball being too short, or the eye lens being unable to focus

• short sight, caused by the eyeball being too long, or the eye lens being unable to focus

• Range of vision - the eye can focus on objects between the near point and the far point.

• Comparison between the structure of the eye and the camera.

• The power of a lens is given by: P = 1 ÷ f

• The focal length of a lens is determined by:

• the refractive index of the material from which the lens is made

• the curvature of the two surfaces of the lens

• For a given focal length, the greater the refractive index, the flatter the lens. This means that the lens can be manufactured thinner.

• Total internal reflection and critical angle.

• refractive index = 1 ÷ sin c

• Visible light can be sent along optical fibres.

• The laser as an energy source for cutting, cauterising and burning. 