09 - Total Internal Reflection

Thursday 13 June 2024 1
3.2 – Total Internal Reflection Learning objective: explore what is total internal
reflected and its real-life applications.
Starter Success criteria:

 Recall what is reflection
 Understand concept of total internal reflection and
1. True or false: speed of light decreases as it enters a less dense medium. critical angle
 Explore real-life application of TIR
2. What is a refractive index of a medium?
3. If the angle of incidence is 42 degrees and angle of refraction is 31

degrees, what would be the refractive index of this material?
Challenge Support Video

4. Explain using wavefronts why refraction takes place. Support
Keywords
Total Internal Reflection, Critical Angle,
3.2 – Total Internal Reflection
Starter Purple Pen: Self-Assessment
1. True or false: speed of light decreases as it enters a less dense medium.
False – speed of light increases – less resistance.
2. What is a refractive index of a medium?
Ability of a medium to bend light
3. If the angle of incidence is 42 degrees and angle of refraction is 31 degrees, what would be the refractive
index of this material?
1.3
Challenge
4. Explain using wavefronts why refraction takes place.
Wavefronts enter medium at different times causing one part to travel slower than the other bending the motion
of light.
3
Waves
Learning Journey
1.1 – Describing Waves
1.2 – Wave Equation
1.3 – Types of Waves
1.4 – Electromagnetic Spectrum
2.1 – Sound Waves

2.2 – Measuring Sound Waves
2.3 – Assessment
3.1 – Reflection
3.3 – Refraction
Introduction
Light entering the prism is totally internally reflected twice. It emerges from the prism travelling back in the
direction from which it originally came – like in bicycle or car reflectors.
Introduction
Images produced by prisms are often brighter and clearer than those produced by mirrors. A periscope that
uses prisms to reflect the light is called a prismatic periscope.
Light passes through the surface AB of the first prism at 90 O and so does not change direction. It then strikes
the surface AC of the prism at an angle of 45O.
Critical angle for glass is 42O so the ray is totally internally reflected and is turned through 90O.
Task: explain what is critical angle and how it is linked to total internal
reflection?
Critical Angle
Investigation
Task: investigate how total internal reflection is used in the following 3 applications:
Binoculars
Optical Fibres
Endoscope
Some points to include:
• What is each application.

• What each is used for.
• Draw a diagram of how light rays travel in each application.
Binoculars Purple Pen: Self-Assessment
Light entering the prism is totally internally reflected twice. It emerges from the prism travelling back in the
direction from which it originally came – like in bicycle or car reflectors.
Each side of a pair of binoculars contains two prisms to totally internally reflect the incoming light.
Optical Fibres Purple Pen: Self-Assessment
One of the most important application – very thin piece of fibre composed of two different types of glass;
centre is made of a glass with high refractive index and the surrounding glass lower
As the fibres are very narrow, light entering the inner core always strikes the boundary of the two glasses at
an angle that is greater than the critical angle – no light escapes across this boundary – therefore acts as a
‘light pipe’ providing a path even when fibre is curved.
Optical Fibres Purple Pen: Self-Assessment
Modern telecommunications systems use optical fibres rather than copper wire to transmit messages as less
energy is lost. Electrical signals from a telephone are converted into light energy produced by tiny lasers –
these send pulses of light into the ends of optical fibres.
Light-sensitive detector at the other end changes the pulses back into electrical signal which then flow to the
telephone receiver.
Endoscope
Light passes through two layers of air with different temperatures. Desert sun heats the sand, which in turn
heats the air just above it.
Hot air bends light rays and reflects the sky.
When seen from the distance, different air masses colliding with each other act like a mirror.
When light moves through the cold air and into the layer of hot air it is refracted.
Endoscope Purple Pen: Self-Assessment
Doctors use periscopes to see inside the body and engineers to see hard-to-reach parts of machinery.
Light travels down one bundle of fibres and shines on the object being viewed – light reflected by the object
travels up a second bundle of fibres – an image is created by eyepiece.
13
Plenary – Critical Thinking Grid

Challenge: connect 5
colours based on your
learning in the lesson.
Learning objective:
explore what is total internal
reflected and its real-life
applications.
Success criteria:
 Recall what is reflection
 Understand concept of
total internal reflection and
critical angle
 Explore real-life
application of TIR

09 - Total Internal Reflection

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Thursday 13 June 2024 1

Starter Success criteria:

2. What is a refractive index of a medium?

3. If the angle of incidence is 42 degrees and angle of refraction is 31

Challenge Support Video

1. True or false: speed of light decreases as it enters a less dense medium.

False – speed of light increases – less resistance.

2. What is a refractive index of a medium?

Ability of a medium to bend light

2.1 – Sound Waves

Some points to include:

• What is each application.

Hot air bends light rays and reflects the sky.

Plenary – Critical Thinking Grid

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