IGCSE UNIT 2 LIGHT Cambridge IGCSE Physics Adapted

IGCSE UNIT 2 LIGHT Cambridge IGCSE Physics Adapted by Science Department Great Neck North High School

Introduction to Light What is a luminous object? Anything that gives of light.

Luminous Objects

Rays and Beams Light travels in _______ � This is why we have shadows, the light does not bend around an obstacle � are represented in diagrams by an arrow are a stream of light that consists of many � rays

Beams of Light Arrows must be straight lines � Using a straight edge is often necessary _____have to be parallel

Beams of Light striking a material surface � Incident light is either Reflected ________________ Refracted _________________ Absorbed _________________ Warms it up

Reflection Bouncing off a boundary or surface � Particles or matter Atoms Molecules Balls � Waves or energy Light Sound Heat

Reflection of Light Plane mirror � Microscopically _______ and ______ surface that reflects light Specular reflection

Reflection of Light

Reflection of an Ambulances often have their name on the front written backwards. Why do you think this is?

Reflection of Light Plane mirror image formation � Reflects light from the ______ to the _____ Plane mirror image characteristics � ___________________ Back to front � _______ distance behind the mirror as the object is in front � _______ size, shape, and color � _______ vertical orientation

Protractor Used to measure angles

Law of Reflection _________________ � _____

Question Which letter correctly shows reflection?

Lateral Image Inversion http: //youtu. be/Ap. YVb. EAPSTo

Image Location

What is the smallest mirror you need to see your whole body? Half your height!

Line of Sight

Line of Sight

Practice Exam Question

Refraction of Light Refraction is the _____ of light as it passes from one material into another

Refraction of Light

Refraction of Light Occurs because the ____________ � Angle of incidence ( i) Angle from the normal line that the light strikes the border between the two substances � Angle of refraction ( r) Angle from the same normal line that the light travels through the new medium

Refraction of Light Refraction

Refraction of Light Object submerged in water

Refraction of Light box and transparent block

Refraction of Light

Refraction of Light slows down as it goes from air to glass/water

Refraction and Fishermen Why do fishermen aim at the tail of the fish while fishing with a spear?

Real and Apparent depth

Real and Apparent Depth If a fisherman aims his spear along the line where he thinks the head of the fish is, he will miss the body of the fish (dotted line)!

Real and Apparent Depth If a fishermen aims along the line where he thinks the tail of the fish is, he will be able to hit the body of the fish (dotted line)!

Critical Angle The angle of incidence at which the angle of refraction is _____ � The light travels along the edge of the material

Refraction of Light Internal reflection �A fraction of the light is reflected back into the material The remaining light is _____ Total internal reflection � The inside surface of the material behaves like a mirror reflecting all the light back into the material Angle of incidence_____critical angle Angle of incidence = angle of reflection

Refraction of Light total internal reflection

Example of Total Internal Reflection: Fiber Optics

Total Internal Reflection

Uses of Fiber Optics Communications: sending information along a light beam. Ex. Telephone, television, radio, computer networks, etc. Endoscopy: seeing down inside a patient’s body Illuminating road signs using only one bulb

Example of Total Internal Reflection: Periscope

Practice Exam Question The figure below shows part of the path of a ray of light through a glass block. The critical angle for the glass/air boundary is 42°. State the name that describes what is happening to the ray � At A, ____________________ � At B, ____________________ On the figure, draw the path of the ray after it has reached C.

Optical Lenses Curved pieces of glass that refract light

Lenses – Observation Activity There are two lenses being passed around. One that is thick in the middle ______and one that is thin in the middle _______Write down your observations of each.

Thin Converging Lens

Thin Converging Lens Causes parallel light passing through the lens to refract and cross the principal axis at a fixed point known as the focal point

Thin Converging Lens Principal focus (focal point) � Point where light rays intersect the _______ Light is focused at this point Focal length � Distance from the_____of the lens to the principal focus

Thin Converging Lens Draw three rays to determine location, size, and orientation of the image � Line traveling parallel to the principal axis and is refracted so that it passes through the principal focal point on the other side of the lens � Line travels through the principal focal point on the same side of the lens as the object and is refracted by the lens so that it travels parallel to the principal axis on the other side of the lens � Line travels through the center of the lens

Thin Converging Lens

Thin Converging Lens

Virtual Images Virtual images cannot be projected onto a screen � The rays appear to come from the object

Real Images Real images can be projected onto a screen � The light rays come directly from the object and actually pass through the lens or refracting material

Dispersion of Light White light is ______ (separated) into the colors of the rainbow � Occurs because different ________ __of light are diffracted at slightly different angles

Mirages A mirage occurs on very hot days when a layer of hot, low density air lies on the ground. Light from the sky will be totally internally reflected at this layer and so you see what looks like a pool of water – it’s actually a reflection of the sky! http: //www. youtube. com/watch? v=Hz. IBmu. LHMSE&list=UUzei. F O 28_167 DXW--p. N-p. AA&index=10&feature=plcp

Mirages also occur in very cold countries. See if you can explain why. In the picture below the mirage appears in the sky and the polar bear seems to be flying upside down!