Year 9 Half-Yearly Exam Revision - Waves

• Common properties of waves • Sound waves • Light waves and EM spectrum

What is the particle model of matter?

1. All substances are made of particles

2. The particles are attracted to each other (some strong

Apply the particle model of matter to the 3 states of matter

Solids: • Little energy

What is a wave?

A travelling distubrance of energy without the net transfer of particles E.g → Dropping a stone in water creates ripples that travel outward

What is an energy transformation?

Conversion of energy from one form to another E.g → Light energy to chemical energy during photosynthesis

What is an energy transfer?

Movement of energy from one place to another without changing form E.g → Heat energy from a gas flame transferred to a saucepan

Define propagate

To spread energy from one place to another. When waves propagate energy

What is a mechanical wave?

Waves that need a medium

Mechanical vs Electromagnetic Wave

Mechanical waves - Need a medium; can travel through a vacuum E.g. → Radio waves, ultraviolet

Speed of electromagnetic waves in a vacuum vs Speed of sound in air

• Speed of light → approx 3 x 10⁸ m/s (299 792 458 m/s) • • • Speed of sound → approx 343 m/s in air at 20℃ This difference causes us to often see lighting before we see the thunder

Transverse vs Longitudinal Waves

Transverse Waves - Particles in the medium move perpendicular to wave motion/ transfer of energy E.g. → Water waves

Define wavelength (λ)

Distance between two consecutive crests (for transverse waves) or compressions (for longitudinal waves)

Define amplitude (A)

Maximum displacement of a particle from its rest position (crest or trough in a transverse wave). Larger amplitude means more energy. Measured in cm or m

Define crest

A position of maximum upward displacement of a particle - the 'top of the wave'

Define trough

A position of maximum downward displacement of a particle - the 'bottom of the wave'

Define frequency (f)

Number of waves passing a point per second

Define wave speed (v)

How fast a wave travels

Define period (T)

The time it takes a source to produce a complete wave. This is the same as the time taken for a complete wave to pass a given point. The period is measured in seconds

Define compression

Where particles are closest together; areas of high pressure/ density

Define rarefraction

Where particles are furthest apart; areas of low pressure/ density

Relate wave features to sound waves

• Pitch refers to the frequency of a sound (higher frequency = higher pitch) • Loudness of sound waves depends on amplitude (greater amplitude = louder sound) • Wave speed depends on the medium the sound is travelling through (highest in solids

Relate wave features to light waves

• Higher frequency radiation in the electromagnetic spectrum carry higher energy intensity and hence can penetrate objects

Formula for relationship between velocity

frequency and wavelength

What are sound waves?

Vibrations create sound waves. Sound waves are mechanical longitudinal waves composed of compressions and rarefactions that require a medium for propagation

• As particles in longitudinal waves vibrate back and forth

Explain a displacement-time graph

Representing sound waves (longitudinal waves) as transverse waves on a displacement-time graph allows us to measure the particle displacement from equilibrium

Investigate traditional instruments

Digeridoo → Made from hollowed out eucalytpus branches • When the player's lips vibrate at one end

Describe how the human ear works

1. Outer ear → Sound energy is collected by auricle and chanelled into the ear canal
2. The sound energy is passed on to the eardrum as kinetic energy - it starts to vibrate with the changing pressure of air particles
3. Middle ear → The ear drum passes the energy on to the ossicles (the three smallest bones in the human body—the malleus (hammer)

Identify and label parts of the human ear

What is the Doppler effect?

A change in an observed frequency due to the movement of a sound's source relative to the observer (normally starting high pitch

Identify situations where the Doppler effect can be observed

Emergency vehicles - an ambulance or police car siren sounds higher-pitched as it drives toward you and drops to a distinctly lower pitch as it passes and moves away Passing vehicles - the engine of a speeding motorcycle sounds high-pitched as it apporaches

Describe how sound waves can be used in medical diagnosis

Ultrasound for pregnancy

Absorpment of light

Light can be absorbed by different surfaces High abosrbance: black asphalt

Ray diagrams for reflection (plane surfaces)

The law of reflection states the angle of incidence (i) = the angle of reflection (r)

• When measuring these angles

we measure the angle of reflection from the reflected ray to the normal. • Almost all light from the object is reflected. The image appearing behind the mirror is the same distance away and same size as the object

but is laterally inverted.

Ray diagrams for reflection (curved surfaces)

Curved mirrors may be a. concave (curved inwards) or b. convex (curved outwards). They also follow the law of reflection

Define refraction

The bending of light when it passes from one medium of different optical density to another medium. When light travels from one transparent medium to another

Examples of refraction

• Viewing underwater objects • Rainbows • Lenses & eyeglasses • Optical fibres

Use Snell's law

The ratio of the sine of the angle of incidence in refraction to the sine of the angle of refraction is called the refractive index of the boundary. Snell's law defines the relationship between the angles of incidence (O1) and angles of refraction (O2). It states the ratio of the sines of the angles is equal to the inverse ratio of the refractive indices (n1

Dispersion of white light through a prism

A prism is a transparent optical element with flat

Ray diagram of light in convex lenses

Ray diagram of light in concave lenses

State common applications for concave and convex lenses

Concave - • Makeup mirrors • Corrective eyeglasses (Myopia - nearsightedness) • Camera lenses • Binoculars • Vehicle headlights Convex - • Magnifying glasses • Corrective eyeglasses (Hyeropia - farsightedness) • Microscopes & telescopes • Blind-spot mirrors • Projectors

Ray diagram of total internal reflection

Total internal reflection only occurs when: • The rays are travelling in a dense medium towards a less-dense medium

Example of a practical use of total internal reflection

Bicycle reflectors and 'cats eyes' reflectors on roads → built so that they reflect back the light from a car headlight

Describe the scattering of light

Rough surfaces - When parallel light rays hit uneven or rough surfaces

Describe the structure and function of each component of the eye

1. Ciliary muscles - contract to thin the lens when viewing distant objects
2. Suspensory ligaments - attach the ciliary muscle to the lens
3. Pupil - the opening through which light travels towards the lens. The iris opens and closes to control its size
4. Iris - the coloured ring of muscle that opens and closes to control the amount of light entering the pupil
5. Cornea - refracts the incoming light

How does light enter your eye?

1. Light reflected from your surroundings enters your eye and is refracted as it passes through the transparent outer surface of the eye (the cornea

however

the brain processes the signals coming from the retina so that you see things the right way up.

Describe the 7 types of EM waves and their order in terms of increasing frequency/ decreasing wavelength: First 3

Radio - • Low in energy intensity • Used in: TV

microwaves used in radar

wireless internet

mobile phone communication • Frequency of radio waves causes electrons in receiving antennas of radios and TVs to vibrate at same frequency

results in sound and images being produced in these devices Microwave - • Absorbed by water/fat to create heat • Cause polar molecules (like water) to vibrate rapidly

Describe the 7 types of EM waves and their order in terms of increasing frequency/ decreasing wavelength: Middle

• Represents only a very small part of electromagnetic spectrum • Contains all colours of rainbow • Necessary for vision in humans

Describe the 7 types of EM waves and their order in terms of increasing frequency/ decreasing wavelength: Last 3

UV -

• Invisible to the human eye
• Essential for vitamin D production in the body
• More energetic than visible light

causes tanning and potentially sunburn with prolonged exposure

• Long-term exposure can increase the risk of skin cancer
• Some sunscreens contain chemicals that absorb UV light to protect the skin
• Used in water treatment facilities to kill pathogens and in hospitals to sterilize instruments X-rays -
• High energy allows them to pass through human tissues

used in medical imaging

• Shadows formed on photographic film indicate denser tissues like bones and tumors
• CT/CAT scanners utilize rotating X-ray machines for detailed imaging of tissues
• Employed in cancer treatment via radiotherapy to target cancer cells
• Industrially

X-rays detect weaknesses in metals

used in medical imaging

• Shadows formed on photographic film indicate denser tissues like bones and tumors
• CT/CAT scanners utilize rotating X-ray machines for detailed imaging of tissues
• Employed in cancer treatment via radiotherapy to target cancer cells
• Industrially

X-rays detect weaknesses in metals

Explain the difference between emission and absorption spectra

Emission spectrum - Shows the specific wavelengths of light or energy released by an excited substance

How can the chemical composition of stars be determined?

Every element absorbs and emits light at specific

How can a star's relative motion to the Earth be determined?

Measuring shifts in its light spectrum

Outline Hubble's contribution to our understanding of the nature of the universe

In the 1920s