LENSES A lens is defined as - A ground or molded piece of glass, plastic, or other transparent material with opposite surfaces either or both of which are curved, by means of which light rays are refracted so that they converge or diverge to form an image.

LENSES Lenses can change the appearance of objects, making images appear larger or smaller than the object or making them upside down or even misshapen BECAUSE OF REFRACTION!

makes parallel light rays come together LENSES A lens is a thin, transparent piece of glass or plastic that has at least one curved side. The curved side or sides may be concave or convex. A Converging Lens A Diverging Lens makes parallel light rays come together makes parallel light rays move apart

Since lenses have 2 sides, they have a focal point on each side. CONVERGING LENSES principal Focus secondary principal Focus Since lenses have 2 sides, they have a focal point on each side. The secondary principal focus is on the same side of the lens as the incident rays

CONVERGING LENSES F F’ 2F 2F’ There is also 2F and 2F’. These two points are twice the distance away from the optical centre than the focus points.

CONVERGING LENSES 3 TYPES OF RAYS 1) Any ray that enters a lens parallel to the principal axis will pass through the focal point on the other side of the lens. 2) Any ray that travels through the centre of the lens will keep travelling in the same direction. 3) Any ray that enters the lens from the focal point will leave the lens parallel to the principal axis.

CONVERGING LENSES 1) Any ray that enters a lens parallel to the principal axis will pass through the focal point on the other side of the lens. F F’

CONVERGING LENSES 2) Any ray that travels through the centre of the lens will keep travelling in the same direction. F F’

CONVERGING LENSES 3) Any ray that enters the lens from the focal point will leave the lens parallel to the principal axis. F F’

CONVERGING LENSES Draw the ray diagram for this pencil to locate its image (you need 2 rays) , , 2F 2F

Draw the ray diagram for this pencil CONVERGING LENSES Draw the ray diagram for this pencil (you need 2 rays) 2F , , 2F

Draw the ray diagram for this pencil CONVERGING LENSES Draw the ray diagram for this pencil (you need 2 rays) 2F , , 2F

Draw the ray diagram for this pencil CONVERGING LENSES Draw the ray diagram for this pencil (you need 2 rays) 2F , , 2F

CONVERGING LENSES 2F 2F If the object is at 2F’… , , SALT -Same -Inverted -At 2 F -Real

CONVERGING LENSES The first lens known to be used was a converging lens called a reading stone. Reading stones formed images that were upright and larger than the object. How can a converging lens produce both upright and inverted images?

CONVERGING LENSES Draw the ray diagram for this pencil to locate its image (you need 2 rays) , , 2F 2F

CONVERGING LENSES Draw the ray diagram for this pencil to locate its image (you need 2 rays) , , 2F 2F

CONVERGING LENSES Draw the ray diagram for this pencil to locate its image (you need 2 rays) , , 2F 2F

CONVERGING LENSES Draw the ray diagram for this pencil to locate its image (you need 2 rays) , , 2F 2F

CONVERGING LENSES 2F 2F If the object is between F’ and the lens… , , SALT -Larger -Upright -Behind the lens -Virtual

DIVERGING LENSES

Since lenses have 2 sides, they have a focal point on each side. DIVERGING LENSES Since lenses have 2 sides, they have a focal point on each side. The secondary principal focus is on the same side of the lens as the incident rays

DIVERGING LENSES

DIVERGING LENSES Optical centre O 2F F F’ 2F’ The same focal points as those for converging lenses, except the principal focus is on the same side as where the incident rays are coming from

DIVERGING LENSES 3 TYPES OF RAYS 1) Any ray parallel to the principal axis is refracted as if it had come through the principal focus (F) 2) A ray that appears to pass through the secondary principal focus (F’) is refracted parallel to the principal axis 3) A ray through the optical centre (O) continues straight through its path

DIVERGING LENSES 1) Any ray parallel to the principal axis is refracted as if it had come through the principal focus (F) F’ F 2F’ 2F O

DIVERGING LENSES 2) A ray that appears to pass through the secondary principal focus (F’) is refracted parallel to the principal axis F’ F 2F’ 2F O

DIVERGING LENSES 3) A ray through the optical centre (O) continues straight through its path F’ F 2F’ 2F O

DIVERGING LENSES Draw the ray diagram for this pencil to locate its image (you need 2 rays) F’ F 2F’ 2F O

DIVERGING LENSES Draw the ray diagram for this pencil to locate its image (you need 2 rays) F’ F 2F’ 2F O

DIVERGING LENSES Draw the ray diagram for this pencil to locate its image (you need 2 rays) F’ F 2F’ 2F O

DIVERGING LENSES Draw the ray diagram for this pencil to locate its image (you need 2 rays) F’ F 2F’ 2F O

DIVERGING LENSES Draw the ray diagram for this pencil to locate its image (you need 2 rays) F’ F 2F’ 2F O

DIVERGING LENSES For ALL images from diverging lenses… SALT -Smaller -Upright -On the same side of the lens as the object -Virtual