TIR and critical angle

TIR and critical angle

By Malcolm Harrison

Objectives: Students will be able to perform calculations regarding TIR and critical angles

Some text here about the topic of discussion

Multiple Choice

Total Internal Reflection can only occur when light is traveling from a high index to a low index

• True

• False

Open Ended

Glass has a critical angle of 41⁰. Explain what this means.

Multiple Choice

If Total Internal Reflection occurs the light will bounce back at the same angle it came in

• True

• False

Open Ended

Refractive index and critical angle

Multiple Choice

If light hits at an angle larger than the critical angle it will refract and pass through the material

• True

• False

Multiple Choice

Diamond has a refractive index of 2.42. Find its critical angle.

• 24.4⁰

• 20.4⁰

• 25⁰

• 30⁰

Multiple Choice

Light travels from glass (n=1.66) to water, what is the critical angle for these two mediums?

• 53.2

• 48.8

• 37

• not possible

Multiple Choice

Light travels from air to water (n=1.33), what is the critical angle?

• 48.8

• 46.4

• 52.4

• not possible

Fill in the Blanks

The refractive index of a transparent material is 2. Find its critical angle.

Multiple Choice

Light travels from oil (n=1.48) to water at an angle of 60 degrees relative to the normal. What will happen to the light?

• reflect back at an angle of 60 degrees

• refract through at an angle of 74.5 degrees

• refract through at an angle of 51.1 degrees

• reflect back at angle of 30 degrees

Multiple Choice

If the refractive index were less than 2, would the critical angle be less or greater than before?

• Yes, because sin c would be less.

• No, because sin c would be less

• yes because sin c would be more

• no because sin c would be more

Multiple Choice

Refraction occurs when light changes mediums, but does not change speeds

• True

• False

Multiple Choice

The higher the index of refraction, the faster light travels in that medium

• True

• False

Dispersion

Multiple Choice

Light traveling from a higher index of refraction to a lower index of refraction will bend towards the normal (refract at a smaller angle)

• True

• False

Prism

*A prism is a triangular block of glass or plastic.

*The sides of the prism are not parallel.

*So, when light is refracted by prism, it comes out in a different direction.

Multiple Choice

Light traveling from a low index of refraction to a higher index of refraction will get slower and bend away from the normal (refract at an larger angle)

• True

• False

• If a beam of white light is passed through a prism, it splits into a range of colours called spectrum.

Multiple Choice

What is the speed of light in ice (n=1.309)

• 2.29 * 10^8 m/s

• 2.43 *10^ 8 m/s

• 4.36 * 10^-9

• 4.36 *10^8 m/s

Multiple Choice

Which of the colours gets most deviated from the incident ray?

• red

• violet

• yellow

Multiple Choice

What is the index of refraction for a material that allows light to travel at 2.8 *10⁸ m/s?

• 1.07

• .67

• 1.5

• not possible

Poll

What might be the reason for dispersion?

• different colours have different wavelength

• different colours have same speed everywhere

• different colours travel with different speed in a medium

• The angle of incidence determines the dispersion

Multiple Choice

Find the angle of refraction for a ray of light that enters water (n=1.33) from glass (n=1.5) at an angle of 25 degrees to the normal.

• 22

• 28.5

• 57.5

• 32.8

Multiple Choice

Which of the colour in the spectrum will have largest refractive index for glass?

• Orange

• Violet

• Red

• Green

Multiple Choice

Light traveling from air to some unknown material makes an angle of 40 degrees to the normal and refracts at an angle of 26 degrees, what is the index of refraction of the new material?

• 1.47

• .68

• 1.2

• 1.67

Refractive index of different colours

n = velocity in vacuum/ velocity in medium

Also V=nλ

Violet has least wavelength.

So it has least speed.

Hence refractive index (n= c/v) will be maximum for violet.

Multiple Choice

A ray of light enters the top of a glass of water at an angle of 36 degrees with the vertical. What is the angle between the refracted ray and the vertical?

• 2.26 degrees

• 26.2 degrees

• 51.4 degrees

• 36.5 degrees

Multiple Choice

A person shines a light at a friend who is swimming underwater. If the ray in the water makes an angle of 36.2 with the normal, what is the angle of incidence?

• 26.4 degrees

• 2.25 degrees

• 51.8 degrees

• not possible