PHYSICS – Total Internal Reflection and Lenses

LEARNING OBJECTIVES Core Describe the formation of an optical image by a plane mirror, and give its characteristics Recall and use the law angle of incidence = angle of reflection Describe an experimental demonstration of the refraction of light Use the terminology for the angle of incidence i and angle of refraction r and describe the passage of light through parallel- sided transparent material Give the meaning of critical angle Describe internal and total internal reflection Describe the action of a thin converging lens on a beam of light Use the terms principal focus and focal length Draw ray diagrams for the formation of a real image by a single lens Describe the nature of an image using the terms enlarged/same size/diminished and upright/inverted Supplement Describe the formation of an optical image by a plane mirror, and give its characteristics Recall and use the law angle of incidence = angle of reflection Recall and use the definition of refractive index n in terms of speed Recall and use the equation sin I / sin r=n Recall and use n = 1 / sin c Describe and explain the action of optical fibres particularly in medicine and communications technology Draw and use ray diagrams for the formation of a virtual image by a single lens Use and describe the use of a single lens as a magnifying glass Show understanding of the terms real image and virtual image

Refraction of light by a semi-circular block. Incident Ray Refracted Ray I R Angle of Incidence Angle of Refraction

Refraction of light by a semi-circular block. Incident Ray Refracted Ray I R Angle of Incidence Angle of Refraction When a ray of light travels through a semi-circular block, the ray will be refracted ………

Refraction of light by a semi-circular block. Incident Ray Refracted Ray I R Angle of Incidence Angle of Refraction When a ray of light travels through a semi-circular block, the ray will be refracted ……… Reflected Ray …… but there will also be some reflection.

Refraction of light by a semi-circular block. Incident Ray Refracted Ray Reflected Ray As the incident ray approaches the ‘critical angle’ (approximately 42 o ) the refracted ray travels at right- angles to the normal. There is now more internal reflection

Refraction of light by a semi-circular block. Incident Ray Reflected Ray If the incident ray now enters the block at an angle greater than the critical angle (42 o ) no light is refracted.

Refraction of light by a semi-circular block. Incident Ray Reflected Ray If the incident ray now enters the block at an angle greater than the critical angle (42 o ) no light is refracted. All light is now reflected at the boundary. This is known as TOTAL INTERNAL REFLECTION

Refraction of light by a semi-circular block. Incident Ray Reflected Ray If the incident ray now enters the block at an angle greater than the critical angle (42 o ) no light is refracted. All light is now reflected at the boundary. This is known as TOTAL INTERNAL REFLECTION MediumCritical angle Water49 o Perspex42 o Glass41 o Diamond24 o

Refraction Calculations

Snell’s Law When light is refracted, an increase in the angle of incidence i produces an increase in the angle of refraction r. Supplement

Refraction Calculations Snell’s Law When light is refracted, an increase in the angle of incidence i produces an increase in the angle of refraction r. Supplement Sin i = constant Sin r

Refraction Calculations Snell’s Law Supplement Air Glass i = 15 o r = 10 o sin 15 o = 0.26 sin 10 o = 0.17 = 1.5

Refraction Calculations Snell’s Law Supplement Air Glass i = 15 o r = 10 o sin 15 o = 0.26 sin 10 o = 0.17 = 1.5 i = 45 o r = 28 o sin 45 o = 0.71 sin 28 o = 0.47 = 1.5

Refraction Calculations Snell’s Law Supplement Air Glass i = 15 o r = 10 o sin 15 o = 0.26 sin 10 o = 0.17 = 1.5 i = 45 o r = 28 o sin 45 o = 0.71 sin 28 o = 0.47 = 1.5 i = 60 o r = 35 o sin 60 o = 0.87 sin 35 o = 0.57 = 1.5

Refraction Calculations Snell’s Law Supplement …and Refractive Index

Refraction Calculations Snell’s Law Supplement …and Refractive Index Refractive Index = Sin i Sin r

Refraction Calculations Snell’s Law Supplement …and Refractive Index Refractive Index = Sin i Sin r Air Water i = 45 o RI = 1.33 ?

Refraction Calculations Snell’s Law Supplement …and Refractive Index Refractive Index = Sin i Sin r Air Water i = 45 o RI = 1.33 ? RI = sin i sin r 1.33 = sin 45 o sin r sin r = sin 45 o 1.33 sin r = r = 32 o

Refraction Calculations Snell’s Law Supplement …and Refractive Index…and Critical Angles!

Refraction Calculations Snell’s Law Supplement …and Refractive Index…and Critical Angles! If the angle of incidence is greater than the critical angle, we will get total internal reflection.

Refraction Calculations Snell’s Law Supplement …and Refractive Index…and Critical Angles! Incident Ray Refracted Ray Critical angle c If the ray direction is reversed, the angle of incidence is now 90 o, and the angle ‘c’ is now the angle of refraction (critical angle).

Refraction Calculations Snell’s Law Supplement …and Refractive Index…and Critical Angles! Incident Ray Refracted Ray Critical angle c If the ray direction is reversed, the angle of incidence is now 90 o, and the angle ‘c’ is now the angle of refraction (critical angle). RI = sin i = sin90 o sin c sin c

Refraction Calculations Snell’s Law Supplement …and Refractive Index…and Critical Angles! Incident Ray Refracted Ray Critical angle c If the ray direction is reversed, the angle of incidence is now 90 o, and the angle ‘c’ is now the angle of refraction (critical angle). RI = sin i = sin90 o sin c sin c RI = 1 sin c = 1 sin c RI

Refraction Calculations Snell’s Law Supplement …and Refractive Index…and Critical Angles! Incident Ray Refracted Ray Critical angle c If the ray direction is reversed, the angle of incidence is now 90 o, and the angle ‘c’ is now the angle of refraction (critical angle). RI = sin i = sin90 o sin c sin c RI = 1 sin c = 1 sin c RI If the RI of glass = 1.5: sin c = 1 = 0.67 c = 42 o 1.5

Refraction Calculations Snell’s Law Supplement …and Refractive Index…and Critical Angles! Incident Ray Critical angle c If the RI of glass = 1.5: sin c = 1 = 0.67 c = 42 o 1.5 The refractive index of a medium is usually denoted as ‘n’. For a medium of refractive index n: sin c = 1 n

Refraction Calculations Snell’s Law Supplement …and Refractive Index…and Critical Angles! Incident Ray Critical angle c If the RI of glass = 1.5: sin c = 1 = 0.67 c = 42 o 1.5 The refractive index of a medium is usually denoted as ‘n’. For a medium of refractive index n: sin c = 1 n eg. What is the critical angle for diamond if the refractive index (n) = 2.42? sin c = 1 = 1 = critical angle for diamond = 24.4 o n 2.42

LEARNING OBJECTIVES Core Describe the formation of an optical image by a plane mirror, and give its characteristics Recall and use the law angle of incidence = angle of reflection Describe an experimental demonstration of the refraction of light Use the terminology for the angle of incidence i and angle of refraction r and describe the passage of light through parallel- sided transparent material Give the meaning of critical angle Describe internal and total internal reflection Describe the action of a thin converging lens on a beam of light Use the terms principal focus and focal length Draw ray diagrams for the formation of a real image by a single lens Describe the nature of an image using the terms enlarged/same size/diminished and upright/inverted Supplement Describe the formation of an optical image by a plane mirror, and give its characteristics Recall and use the law angle of incidence = angle of reflection Recall and use the definition of refractive index n in terms of speed Recall and use the equation sin I / sin r=n Recall and use n = 1 / sin c Describe and explain the action of optical fibres particularly in medicine and communications technology Draw and use ray diagrams for the formation of a virtual image by a single lens Use and describe the use of a single lens as a magnifying glass Show understanding of the terms real image and virtual image

Lenses and Refraction Convex lensConcave lens

Lenses and Refraction Convex lensConcave lens Converging lens Diverging lens

Lenses and Refraction Convex lensConcave lens Converging lens Diverging lens Principal focus Focal length

Lenses and Refraction Convex lensConcave lens Converging lens Diverging lens Principal focus Focal length Principal focus Focal length

Lenses and Refraction Convex lens What happens to light as it passes through the lens?

Lenses and Refraction Convex lens What happens to light as it passes through the lens?

Lenses and Refraction Convex lens What happens to light as it passes through the lens?

Lenses and Refraction Convex lens What happens to light as it passes through the lens? As light passes through the first face of the lens it bends towards the normal (refraction)

Lenses and Refraction Convex lens What happens to light as it passes through the lens? As light passes through the first face of the lens it bends towards the normal (refraction) As light passes through the second face of the lens it bends away from the normal (refraction)

Lenses and Refraction Convex lens What happens to light as it passes through the lens? As light passes through the first face of the lens it bends towards the normal (refraction) As light passes through the second face of the lens it bends away from the normal (refraction)

Lenses and Images ObjectConvex lens Image Rays from a distant object brought to focus on a screen by a convex lens.

Lenses and Images ObjectConvex lens Image Rays from a distant object brought to focus on a screen by a convex lens. The image on the screen is real and inverted (upside- down)

Lenses and Images ObjectConvex lens Image Rays from a distant object brought to focus on a screen by a convex lens. The image on the screen is real and inverted (upside- down) Light rays from a distant object are considered to be parallel to each other, so the image passes through the principal focus.

Lenses and Ray Diagrams - Predicting where a convex lens will form an image. F1F1 F

Lenses and Ray Diagrams - Predicting where a convex lens will form an image. F1F1 F Standard Ray 1 – passes through the centre of the lens object

Lenses and Ray Diagrams - Predicting where a convex lens will form an image. F1F1 F Standard Ray 1 – passes through the centre of the lens Standard Ray 2 – parallel to the principal axis, and then passes through F after leaving the lens. object

Lenses and Ray Diagrams - Predicting where a convex lens will form an image. F1F1 F Standard Ray 1 – passes through the centre of the lens Standard Ray 2 – parallel to the principal axis, and then passes through F after leaving the lens. Standard Ray 3 – passes through F 1, and then leaves the lens parallel to the principal axis. object

Lenses and Ray Diagrams - Predicting where a convex lens will form an image. F1F1 F Standard Ray 1 – passes through the centre of the lens Standard Ray 2 – parallel to the principal axis, and then passes through F after leaving the lens. Standard Ray 3 – passes through F 1, and then leaves the lens parallel to the principal axis. The image produced is real, inverted and smaller than the object. object

Lenses and Ray Diagrams - Predicting where a convex lens will form an image. F1F1 F Standard Ray 1 – passes through the centre of the lens Standard Ray 2 – parallel to the principal axis, and then passes through F after leaving the lens. Standard Ray 3 – passes through F 1, and then leaves the lens parallel to the principal axis. The image produced is real, inverted and smaller than the object. object Only two of the standard rays are required to work out where they go.

Lenses and Ray Diagrams - Predicting where a convex lens will form an image. F1F1 F Standard Ray 1 – passes through the centre of the lens Standard Ray 2 – parallel to the principal axis, and then passes through F after leaving the lens. Standard Ray 3 – passes through F 1, and then leaves the lens parallel to the principal axis. The image produced is real, inverted and smaller than the object. object Only two of the standard rays are required to work out where they go. As the object is moved closer towards the lens, the image becomes bigger and further away.

Uses of Convex Lenses 1. In a projector

Uses of Convex Lenses 1. As a magnifying glass F1F1 F Object between F 1 and lens

Uses of Convex Lenses 2. As a magnifying glass F1F1 F Object between F 1 and lens

Uses of Convex Lenses 2. As a magnifying glass F1F1 F Object between F 1 and lens The image is virtual, upright and magnified. The rays appear to be coming from a position behind the lens. The image is upright and magnified, and it is called a virtual image because no rays actually meet to form it and the image cannot be formed on a screen.

Ray Diagram for a Concave Lens - Predicting where a concave lens will form an image. F

Ray Diagram for a Concave Lens - Predicting where a concave lens will form an image. F object The image is virtual, upright and diminished (smaller than the object).

LEARNING OBJECTIVES Core Describe the formation of an optical image by a plane mirror, and give its characteristics Recall and use the law angle of incidence = angle of reflection Describe an experimental demonstration of the refraction of light Use the terminology for the angle of incidence i and angle of refraction r and describe the passage of light through parallel- sided transparent material Give the meaning of critical angle Describe internal and total internal reflection Describe the action of a thin converging lens on a beam of light Use the terms principal focus and focal length Draw ray diagrams for the formation of a real image by a single lens Describe the nature of an image using the terms enlarged/same size/diminished and upright/inverted Supplement Describe the formation of an optical image by a plane mirror, and give its characteristics Recall and use the law angle of incidence = angle of reflection Recall and use the definition of refractive index n in terms of speed Recall and use the equation sin I / sin r=n Recall and use n = 1 / sin c Describe and explain the action of optical fibres particularly in medicine and communications technology Draw and use ray diagrams for the formation of a virtual image by a single lens Use and describe the use of a single lens as a magnifying glass Show understanding of the terms real image and virtual image

PHYSICS – Total Internal Reflection and Lenses