Wave interactions with matter

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Types of Waves

Light waves (electromagnetic) transmit energy and do not require a medium.
Mechanical waves (e.g., sound, water) transfer energy by moving particles and require a medium.
Light waves are transverse; mechanical waves can be transverse or longitudinal.
Waves can be transmitted, reflected, absorbed, or refracted through materials.

Longitudinal and transverse waves.

Light Waves and Vision

We see objects when light reflects off them and enters our eyes.
Brightness is controlled by wave amplitude; color is determined by wavelength.
Longest visible wavelength appears red; shortest appears violet; the visible spectrum is in rainbow order.
In darkness, no light waves reflect off objects, so we cannot see them.

The visible spectrum, ordered by wavelength.

Sound Waves

Sound is energy transfer from vibrating objects through matter.
Sound waves are mechanical and require a medium.
A vibrating guitar string pushes air particles, creating sound waves that travel to the ear.
Sound waves vibrate the eardrum; the brain interprets these vibrations as sound.

A vibrating guitar string produces a sound wave that reaches the ear.

Reflection of Waves

Reflection occurs when a wave bounces off a surface (e.g., light off a mirror, sound causing echoes).
Even reflection from smooth surfaces produces clear images (mirrors).
Uneven reflection from rough surfaces scatters light, making objects look dull.
For reflection, the angle of incidence equals the angle of reflection.

Angle of incidence, angle of reflection, and the normal at a reflecting surface.

Transmission and Refraction

Transmission is when a wave travels through a medium (e.g., sound through air, light through glass).
Refraction is the bending of light due to a change in speed when moving between media.
A prism refracts white light, separating it into colors because different wavelengths bend at different angles.
Refraction is used in lenses (glasses, microscopes) to focus light for clearer images.

White light entering a glass prism and separating into the colours of the spectrum.

Absorption of Waves

Absorption occurs when a wave is stopped and its energy is converted to heat.
Soundproof walls absorb sound energy, making rooms quieter.
Black pavement absorbs light waves, becoming hotter than lighter surfaces.
Black objects absorb all colors of light; white objects reflect all colors.

Transparent, Translucent, and Opaque Materials

Transparent materials transmit most light (e.g., clear glass).
Translucent materials allow some light through but scatter it (e.g., plastic shopping bag).
Opaque materials absorb or reflect all light, casting shadows (e.g., cardboard).
Shadows form because light travels in straight lines and cannot pass through opaque objects.

Color and Absorption

We see an object's color from the light it reflects; other colors are absorbed.
A red ladybird reflects red light and absorbs all other colors.
Green leaves reflect green light and absorb other colors.
Black spots absorb all colors, reflecting none; black is not a color of light but absence of reflection.

How a green leaf reflects green light and absorbs other colors

How We See Light and Color

Light enters the eye through the pupil, is focused by the cornea and lens.
The retina contains light-sensitive cells that convert light into electrical impulses.
These impulses travel via the optic nerve to the brain, which interprets them as sight.
We see color because different wavelengths are reflected and stimulate cone cells in the retina.

A normal eye focusing light onto the retina.

Speed of Sound in Different Mediums

Sound travels at different speeds depending on the medium: air (346 m/s), water (1498 m/s), steel (5200 m/s).
Sound travels fastest in solids, slower in liquids, and slowest in gases.
This is because particles are closer together in solids, allowing vibrations to transfer more quickly.
In gases, particles are farther apart, so sound energy transfers more slowly.

Particle spacing in solids, liquids and gases.

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1.Light waves are mechanical waves that require a medium to travel through.
Easy
True or false?
2.Which of the following is an example of a mechanical wave?
Easy
- ALight wave
- BSound wave
- CRadio wave
- DX-ray
3.Sound waves travel faster through gases than through solids.
Easy
True or false?
4.Which of the following materials is the best transmitter of sound?
Easy
- AAir
- BWater
- CSteel
- DFoam rubber
5.What happens to the energy of a wave when it is absorbed by a material?
Easy
- AIt is converted to heat energy.
- BIt is reflected back.
- CIt is transmitted through.
- DIt is converted to light energy.
6.A student shines a light ray at a mirror. The angle of incidence is 30°. What is the angle of reflection?
Easy
- A15°
- B30°
- C60°
- D90°
7.Which of the following correctly describes the speed of light in different media?
Easy
- ALight travels faster in glass than in air.
- BLight travels faster in water than in air.
- CLight travels faster in air than in glass.
- DLight travels at the same speed in all media.
8.When light passes from air into glass at an angle, it bends away from the normal.
Easy
True or false?

Mehr Fragen

9.A red filter is placed in front of a white light source. What colour of light emerges from the filter?
Easy
- AWhite
- BRed
- CAll colours except red
- DBlack
10.Which of the following best explains why a green leaf appears green?
Medium
- AIt reflects green light and absorbs all other colours.
- BIt absorbs green light and reflects all other colours.
- CIt transmits green light.
- DIt emits green light.
11.Diffuse reflection occurs when light reflects off a smooth surface.
Medium
True or false?
12.When white light passes through a glass prism, which colour is refracted the most?
Medium
- ARed
- BGreen
- CYellow
- DViolet
13.A student looks at a pencil in a glass of water and it appears bent. This is due to:
Medium
- AReflection
- BRefraction
- CAbsorption
- DTransmission
14.Black objects appear black because they reflect all colours of light.
Medium
True or false?
15.Which of the following is NOT a correct statement about sound waves?
Medium
- ASound waves are mechanical waves.
- BSound waves can travel through a vacuum.
- CSound waves travel faster in solids than in gases.
- DSound waves are produced by vibrating objects.
16.A ray of light strikes a plane mirror at an angle of 40° to the mirror surface. What is the angle of incidence?
Medium
- A40°
- B50°
- C90°
- D140°
17.Which of the following correctly describes how we see an object?
Medium
- ALight from the object enters our eyes directly.
- BLight reflects off the object and enters our eyes.
- CLight is absorbed by the object and then emitted.
- DLight is transmitted through the object to our eyes.
18.In a vacuum, all electromagnetic waves travel at the same speed.
Medium
True or false?
19.A student places a red filter in front of a white light source and then shines the light on a green leaf. What colour will the leaf appear?
Hard
- ARed
- BGreen
- CBlack
- DWhite
20.The angle of incidence and the angle of refraction are always equal when light passes from one medium to another.
Hard
True or false?
21.Which of the following is the correct order of the visible spectrum from longest wavelength to shortest wavelength?
Hard
- ARed, orange, yellow, green, blue, indigo, violet
- BViolet, indigo, blue, green, yellow, orange, red
- CRed, yellow, orange, green, blue, violet, indigo
- DBlue, green, yellow, orange, red, violet, indigo
22.Match each term with its correct definition.
Hard
- Opaque
- Transparent
- Translucent
- Allows all light to pass through
- Allows no light to pass through
- Allows some light to pass through
23.Match each type of wave interaction with its correct description.
Easy
- Reflection
- Absorption
- Transmission
- Refraction
- Wave bounces off a surface
- Wave energy is converted to heat
- Wave passes through a medium
- Wave changes direction due to speed change
24.Arrange the following media in order of increasing speed of sound (from slowest to fastest).
Medium
- Air at 25°C
- Water at 25°C
- Steel
25.Which of the following are examples of mechanical waves? (Select all that apply)
Medium
- ASound waves
- BLight waves
- CWater waves
- DRadio waves
- ESeismic waves
26.Sound waves travel faster through gases than through liquids.
Easy
True or false?
27.Which of the following surfaces would produce the clearest (specular) reflection?
Easy
- AA crumpled piece of aluminium foil
- BA still lake
- CA rough brick wall
- DA frosted glass window
28.Which of the following are true about the absorption of waves? (Select all that apply)
Medium
- AAbsorbed wave energy is converted to heat energy.
- BBlack objects absorb all colours of light.
- CSoundproof walls work by absorbing sound waves.
- DTransparent objects absorb all light.
- EAbsorption can cause an object to appear black.
29.Match each term about how we see objects with its correct description.
Easy
- Retina
- Pupil
- Cornea
- Optic nerve
- Layer of tissue at the back of the eye sensitive to light
- Opening that lets light into the eye
- Transparent layer covering the iris
- Carries nerve impulses to the brain
30.Which of the following statements is correct about the speed of sound in different materials?
Easy
- ASound travels fastest in gases because the particles are far apart.
- BSound travels fastest in solids because the particles are close together.
- CSound travels at the same speed in all materials.
- DSound travels slowest in solids because they are dense.
31.A ray of light passes from air into a glass block at an angle of 30° to the normal. Which statement is correct?
Medium
- AThe light speeds up and bends away from the normal.
- BThe light slows down and bends towards the normal.
- CThe light speeds up and bends towards the normal.
- DThe light slows down and bends away from the normal.
32.A red filter transmits only red light and absorbs all other colours.
Easy
True or false?
33.Which of the following are examples of waves being transmitted? (Select all that apply)
Medium
- AHearing a sound through a wall
- BSeeing your reflection in a mirror
- CLight passing through a glass window
- DSound being absorbed by foam rubber
- EHearing an echo in a canyon
34.What is the relationship between the angle of incidence and the angle of refraction?
Medium
- AThey are always equal.
- BThe angle of refraction is always smaller than the angle of incidence.
- CThe angle of refraction is always larger than the angle of incidence.
- DThere is no relationship.
35.A student is investigating the reflection of light from a mirror. What is the purpose of drawing a normal line on the paper before placing the mirror?
Medium
- ATo measure the angle of incidence and angle of reflection
- BTo make the mirror stand upright
- CTo mark the position of the mirror
- DTo block stray light
36.Complete the sentence.
Easy
When light waves are absorbed by an object, the energy is changed into ____ energy.
37.The speed of sound in air at 25°C is 346 m/s. How far does sound travel in 2 seconds? (Give your answer in metres.)
Medium
38.What is the name for the type of reflection that occurs from a rough surface, producing a blurred image?
Medium
39.What is the term for the imaginary line drawn perpendicular to a reflecting surface at the point of incidence?
Medium
40.The speed of sound in water is 1498 m/s. How long does it take sound to travel 300 m in water? (Give your answer in seconds, correct to two decimal places.)
Medium
41.What is the term for a substance that allows some light to pass through but not all, making it semi-transparent?
Hard
42.The speed of sound in steel is 5200 m/s. How long does it take sound to travel 2600 m through a steel rail? (Give your answer in seconds.)
Medium
43.A student hears an echo from a cliff 2.5 seconds after shouting. The speed of sound in air is 346 m/s. How far away is the cliff? (Give your answer in metres.)
Medium
44.What is the speed of sound in water at 25°C? (Give your answer in m/s.)
Easy
45.Explain why a black object appears black.
Hard
46.Explain why a straw in a glass of water appears bent.
Challenge
47.Describe the difference between specular and diffuse reflection.
Challenge
48.A red car is parked under a blue streetlight. Explain what colour the car appears and why.
Challenge
49.Explain why a white object appears white when white light shines on it.
Hard
50.The speed of sound in air at 25°C is 346 m/s. How far does sound travel in 2 seconds? (Give your answer in metres.)
Medium
- A761 m
- B830 m
- C692 m
- D623 m
51.The speed of sound in water is 1498 m/s. How long does it take sound to travel 300 m in water? (Give your answer in seconds, correct to two decimal places.)
Medium
- A0.2 s
- B2.2 s
- C1.2 s
- D-0.8 s
52.The speed of sound in steel is 5200 m/s. How long does it take sound to travel 2600 m through a steel rail? (Give your answer in seconds.)
Medium
- A1.5 s
- B0.5 s
- C2.5 s
- D-0.5 s
53.A student hears an echo from a cliff 2.5 seconds after shouting. The speed of sound in air is 346 m/s. How far away is the cliff? (Give your answer in metres.)
Medium
- A519.1 m
- B475.8 m
- C389.2 m
- D432.5 m
54.What is the speed of sound in water at 25°C?
Easy
- A1498 m/s
- B1648 m/s
- C1798 m/s
- D1348 m/s
55.A student wants to build a model showing how the transmission of visible light is different from the transmission of sound waves. Which idea should the model show?
Medium
- ALight and sound waves can both be transmitted through empty space.
- BLight can be transmitted through empty space and through matter, but sound can only be transmitted through matter.
- CLight can be transmitted through matter only, while sound can be transmitted through empty space.
- DLight can be transmitted only through empty space, while sound can be transmitted through empty space and matter.
56.The photo shows three everyday materials. Match each material to how it mostly interacts with light.
Medium
- Aluminum foil
- Plastic wrap
- Black towel
- Reflects most of the light
- Transmits most of the light
- Absorbs most of the light
57.The diagram shows a light ray about to strike a shiny metal surface at point X. Which path does the reflected ray take?
Medium
- AUp and to the right
- BUp and to the left
- CStraight down, continuing into the block
- DStraight up, retracing the incoming path

Lernnotizen

## Wave Interactions with Matter Waves (light, sound, water) interact with materials in three main ways: **reflection**, **absorption**, and **transmission**. ### Reflection - **Reflection** is the change in direction of a wave at a boundary between two media, causing the wave to return into the original medium. - **Law of Reflection**: The angle of incidence equals the angle of reflection (θi = θr). The incident ray, reflected ray, and normal all lie in the same plane. - **Specular reflection** occurs on smooth surfaces (e.g., mirrors) and forms clear images. **Diffuse reflection** occurs on rough surfaces and scatters light. - Reflection can cause **echoes** (sound) and is used in sonar, radar, and seismic studies. ### Absorption and Transmission - When a wave hits a material, part of its energy may be **absorbed** (converted to heat) or **transmitted** through the material. - **Transparent materials** (e.g., glass, water) transmit most light; **opaque materials** absorb or reflect it. - The amount of reflection and transmission depends on the **refractive index** of the materials. Light reflects more when moving from a low to high refractive index. ### Light and Sound - **Light** reflects off mirrors (specular) and most surfaces (diffuse). The **eye** detects reflected light to see objects. - **Sound** reflects off hard surfaces, creating echoes. The **ear** detects these reflected waves. ### Key Formulas/Definitions - **Law of Reflection**: θi = θr (angles measured from the normal). - **Normal**: an imaginary line perpendicular to the surface at the point of incidence. ### Examples - Mirror: specular reflection forms a reversed image. - Echo: sound reflects off a distant wall. - Water: light reflects off the surface (partial) and transmits into the water (refraction).

Reflection: The change in direction of a wave at an interface between two different media so that the wavefront returns into the medium from which it originated.
Law of Reflection: The angle of incidence equals the angle of reflection (θi = θr); the incident ray, reflected ray, and normal all lie in the same plane.
Specular reflection: Reflection from a smooth surface where the wave is reflected in a single direction, forming a clear image (e.g., mirror).
Diffuse reflection: Reflection from a rough surface where the wave is scattered in many directions, retaining energy but losing the image.
Absorption: The process by which a wave's energy is taken up by a material, often converted to heat.
Transmission: The passage of a wave through a material.
Normal: An imaginary line perpendicular to the surface at the point of incidence, used to measure angles of incidence and reflection.
Angle of incidence: The angle between the incident wave and the normal to the surface.
Angle of reflection: The angle between the reflected wave and the normal to the surface.
Refractive index: A measure of how much a material slows down light; differences in refractive index cause reflection and refraction at boundaries.

Karteikarten

What are the three main things that can happen when a wave hits a material?

The wave can be reflected, absorbed, or transmitted through the material.

Define reflection of a wave.

Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated.

State the law of reflection.

The angle of incidence equals the angle of reflection, and the incident ray, reflected ray, and normal all lie in the same plane.

What is the difference between specular and diffuse reflection?

Specular reflection (e.g., from a mirror) preserves the image; diffuse reflection scatters light in many directions, losing the image but retaining energy.

Give an example of reflection of sound waves.

Echoes are caused by the reflection of sound waves off surfaces.

What is the normal in the context of reflection?

The normal is an imaginary line drawn perpendicular to the reflecting surface at the point where the incident ray strikes.

What happens to light when it travels from one medium to another with a different refractive index?

Some light is reflected from the interface, and the remainder is refracted (transmitted) into the new medium.

What is total internal reflection?

Total internal reflection occurs when light traveling from a denser medium to a less dense medium strikes the boundary at an angle greater than the critical angle, and all light is reflected back.

How does the phase of reflected light change when reflecting off a material with higher refractive index?

The reflected light undergoes a 180° phase shift.

How does the phase of reflected light change when reflecting off a material with lower refractive index?

The reflected light remains in phase with the incident light.

What type of surface produces specular reflection?

A very smooth surface, like a mirror or calm water, produces specular reflection.

What type of surface produces diffuse reflection?

A rough or uneven surface, like paper or a wall, produces diffuse reflection.

What is absorption of a wave?

Absorption occurs when a wave's energy is taken up by the material, often converting to heat.

What is transmission of a wave?

Transmission is when a wave passes through a material, continuing to propagate on the other side.

How does the human eye detect light?

The eye detects light when reflected or emitted light enters the eye and is focused onto the retina, where photoreceptor cells convert it into signals for the brain.

How does the human ear detect sound?

The ear detects sound when sound waves cause the eardrum to vibrate; these vibrations are transmitted through the middle ear to the cochlea, where hair cells convert them into electrical signals.

What is an echo?

An echo is a reflected sound wave that is heard after the original sound, caused by reflection off a distant surface.

What is sonar?

Sonar uses sound wave reflection to detect objects underwater by sending out pulses and listening for echoes.

What happens to a wave when it is absorbed by a material?

The wave's energy is transferred to the material, often increasing its temperature.

Give an example of transmission of light through a material.

Light passing through a glass window is an example of transmission.

What is the critical angle in total internal reflection?

The critical angle is the angle of incidence above which total internal reflection occurs when light travels from a denser to a less dense medium.

How does a mirror reflect light?

A mirror has a smooth metallic coating that reflects most incident light specularly, producing a clear image.

What is the difference between the incident ray and the reflected ray?

The incident ray is the incoming wave that strikes the surface; the reflected ray is the wave that bounces off the surface.

What is the relationship between the angle of incidence and the angle of reflection?

They are equal: angle of incidence = angle of reflection.

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