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 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. Refracted Ray Angle of Refraction R Angle of Incidence I Incident Ray

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

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

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

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

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

Refraction of light by a semi-circular block. Medium Critical angle Water 49o Perspex 42o Glass 41o Diamond 24o If the incident ray now enters the block at an angle greater than the critical angle (42o) no light is refracted. Incident Ray Reflected Ray All light is now reflected at the boundary. This is known as TOTAL INTERNAL REFLECTION

Refraction Calculations

Refraction Calculations 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.

Refraction Calculations 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. Sin i = constant Sin r

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

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

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

Refraction Calculations Supplement Refraction Calculations …and Refractive Index Snell’s Law

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

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

Refraction Calculations Supplement Refraction Calculations …and Refractive Index Snell’s Law Refractive Index = Sin i Sin r RI = sin i sin r 1.33 = sin 45o sin r = sin 45o 1.33 sin r = 0.532 r = 32o Air i = 45o ? RI = 1.33 Water

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

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

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

Refraction Calculations Supplement Refraction Calculations …and Refractive Index …and Critical Angles! Snell’s Law If the ray direction is reversed, the angle of incidence is now 90o, and the angle ‘c’ is now the angle of refraction (critical angle). Critical angle Incident Ray c Refracted Ray RI = sin i = sin90o sin c sin c

Refraction Calculations Supplement Refraction Calculations …and Refractive Index …and Critical Angles! Snell’s Law If the ray direction is reversed, the angle of incidence is now 90o, and the angle ‘c’ is now the angle of refraction (critical angle). Critical angle Incident Ray c Refracted Ray RI = sin i = sin90o sin c sin c RI = 1 sin c = 1 sin c RI

Refraction Calculations Supplement Refraction Calculations …and Refractive Index …and Critical Angles! Snell’s Law If the RI of glass = 1.5: sin c = 1 = 0.67 c = 42o 1.5 If the ray direction is reversed, the angle of incidence is now 90o, and the angle ‘c’ is now the angle of refraction (critical angle). Critical angle Incident Ray c Refracted Ray RI = sin i = sin90o sin c sin c RI = 1 sin c = 1 sin c RI

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

Snell’s Law Refraction Calculations Supplement Refraction Calculations …and Refractive Index …and Critical Angles! Snell’s Law The refractive index of a medium is usually denoted as ‘n’. For a medium of refractive index n: sin c = 1 n If the RI of glass = 1.5: sin c = 1 = 0.67 c = 42o 1.5 Critical angle Incident Ray c eg. What is the critical angle for diamond if the refractive index (n) = 2.42? sin c = 1 = 1 = 0.413 critical angle for diamond = 24.4o 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 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 lens Concave lens

Lenses and Refraction Convex lens Concave lens Converging lens Diverging lens

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

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

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

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

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

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

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

What happens to light as it passes through the lens? Lenses and Refraction What happens to light as it passes through the lens? Convex 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 Rays from a distant object brought to focus on a screen by a convex lens. Object Convex lens Image

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

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

Lenses and Ray Diagrams - Predicting where a convex lens will form an image. F1 F

Lenses and Ray Diagrams - Predicting where a convex lens will form an image. Standard Ray 1 – passes through the centre of the lens object F1 F

Lenses and Ray Diagrams - Predicting where a convex lens will form an image. 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 F1 F

Lenses and Ray Diagrams - Predicting where a convex lens will form an image. 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 F1 F Standard Ray 3 – passes through F1, and then leaves the lens parallel to the principal axis.

Lenses and Ray Diagrams - Predicting where a convex lens will form an image. 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 F1 F The image produced is real, inverted and smaller than the object. Standard Ray 3 – passes through F1, and then leaves the lens parallel to the principal axis.

Lenses and Ray Diagrams - Predicting where a convex lens will form an image. 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 F1 F The image produced is real, inverted and smaller than the object. Standard Ray 3 – passes through F1, and then leaves the lens parallel to the principal axis. 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. 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 F1 F The image produced is real, inverted and smaller than the object. Standard Ray 3 – passes through F1, and then leaves the lens parallel to the principal axis. As the object is moved closer towards the lens, the image becomes bigger and further away. Only two of the standard rays are required to work out where they go.

Uses of Convex Lenses 1. In a projector

Uses of Convex Lenses 1. As a magnifying glass F1 F Object between F1 and lens

Uses of Convex Lenses 2. As a magnifying glass F1 F Object between F1 and lens

Uses of Convex Lenses 2. As a magnifying glass F1 F 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. F1 F The image is virtual, upright and magnified. Object between F1 and lens

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. object F 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 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