Waves And Cosmology

Types Of Wave

Longitudinal, Transverse

Longitudinal Energy Transfer

Parallel to the direction of particle vibration

Transverse Energy Transfer

At 90° to the direction of particle vibration

Amplitude

Distance from the rest point of a wave to a peak or trough

How a longitudinal wave travels

As a series of compressions and rarefactions

Rarefaction

The part of a wave where particles are spread out

Example of longitudinal waves

Sound

Examples of transverse waves

Light, water

Wavelength

The distance between two like points on a wave, measured in meters

Time period

The time take for one whole wave to form

Frequency

The number of waves in one second

Unit for wavelength

metres (m)

Unit for time period

seconds (s)

Unit for frequency

Hertz (Hz)

Increase pitch of sound

Increase frequency of vibration

Increase volume of sound

Increase amplitude

Human hearing range

approx. between 20 and 20,000 Hz

Ray

A line showing the path taken by a wave with arrows to show the direction of travel

Wavefront

A series of lines at 90° to the ray that show the crests of the wave

Crest

a point on a wave where the displacement is at its maximum above the equilibrium (rest) position

Equation linking wavelength λ (m), frequency F (Hz) and wave speed v (m/s)

wave speed (v) = frequency (F) x wavelength (λ)

Equation linking time period T (s) and frequency F (Hz)

T = 1 / F

Normal

The dotted line in reflection diagrams that is perpendicular to the surface.

Incident Ray

Incoming ray / wave

Reflected ray

Outgoing ray

Angle of Incidence

Angle between incident ray and normal

Angle of reflection

Angle between reflected ray and normal

Law of reflection

angle of incidence = angle of reflection

Echo

Reflection of sound waves

Echolocation

when an echo is used to work out the distance to objects

Distance to objects

(speed of sound wave in medium) x (time it takes for echo) / 2 (because the wave has to go to the object and back)

Varieties of electromagnetic waves in correct order

Radio waves, microwaves, infrared radiation, visible light, ultraviolet, x-ray, gamma ray

Shortest E.M wave

Gamma

Longest E.M wave

Radio

Waves with higher frequency...

have more energy

Radio Waves

Used for communication in radio, television, and mobile phones; generally considered safe.

Microwaves

Utilized in cooking and certain communication technologies; can cause burns if exposure is excessive.

Infrared Radiation

Employed in heating and remote controls; prolonged exposure may lead to skin burns.

Visible Light

The portion of the spectrum visible to the human eye; essential for vision but can cause eye strain.

Ultraviolet Radiation

Used in sterilization and tanning; excessive exposure can lead to skin cancer and eye damage.

X-Rays

Utilized in medical imaging; high doses can increase cancer risk.

Gamma Rays

Employed in cancer treatment; highly penetrating and can cause significant biological damage.

Safety Measures for UV Exposure

Use sunscreen, wear protective clothing, and limit sun exposure during peak hours.

Microwave Safety

Avoid standing close to operating microwaves and ensure appliances are well-maintained.

X-Ray Safety

Minimize exposure time and use lead shields during medical imaging procedures.

Radio Frequency Safety

Limit prolonged exposure to high-intensity radio frequency fields to reduce potential health risks.

Infrared Safety

Use protective eyewear when working with high-intensity infrared sources.

Electromagnetic Spectrum

The range of all types of EM radiation, from radio waves to gamma rays.

Non-Ionizing Radiation

Includes radio waves, microwaves, and visible light; generally less harmful than ionizing radiation.

Ionizing Radiation

Includes X-rays and gamma rays; has enough energy to remove tightly bound electrons from atoms, potentially causing damage.

Preventive Measures for EM Exposure

Implement shielding, maintain safe distances, and use protective equipment when necessary.

Properties of E.M waves

All transverse waves and travel at the same speed in a vaccuum

Refraction

The bending of a wave as it passes at an angle from one medium to another

Refraction of light

Bends towards normal when entering block of glass, bends away from normal when exiting glass into air

Refractive Index

a measure of the light-bending ability of a medium

Relation between refractive index, angle of incidence and angle of refraction

n = sin i (angle of incidence) / sin r (angle of refraction)

Refraction of water waves

water waves travel slower in shallow water and faster when they go into deep water

Water wavelength in shallow water

Shorter

Water wavelength in deep water

Longer

Bending of water in shallow water

Towards the normal

Bending of water in deep water

Away from the normal

Total Internal Reflection

The complete reflection that takes place within a substance.

Condition for Total Internal Reflection (angle)

The angle of incidence of light must be greater than the critical angle.

Condition for Total Internal Reflection (medium)

Ray must be going from a high refractive index material (i.e glass) into a low refractive index material (i.e air)

Doppler Effect

The change in frequency and wavelength of a wave in relation to an observer moving relative to the source.

What happens to the observed wavelength when a source moves towards an observer

The observed wavelength decreases and the frequency increases.

What happens to the observed wavelength when a source moves away from an observer

The observed wavelength increases and the frequency decreases.

Red shift

The phenomenon where light from distant stars shifts towards the red end of the spectrum, indicating they are moving away from us.

Evidence that supports the existence of helium in the Sun

The presence of black lines in the absorption spectrum of sunlight where helium has absorbed light.

What does an increased red-shift in light from distant galaxies indicate?

That the galaxies are moving away from us and that the further away a galaxy is, the faster it is moving away.

What does the red-shift of distant galaxies suggest about the Universe?

It suggests that the Universe is generally expanding.

What is the Big Bang theory?

A theory stating that about 13.8 billion years ago, all matter in the Universe was concentrated in a tiny point that began to expand rapidly.

What is cosmic microwave background radiation (CMBR)?

Radiation thought to be the heat left over from the original explosion of the Big Bang, detected from all parts of the Universe.

What two features of distant galaxies support the Big Bang theory?

All distant galaxies are moving away from us, and the further away a galaxy is, the faster it is moving away.

What is the significance of the pattern of lines in the absorption spectrum of a distant star?

It indicates the presence of elements like helium and shows how the light has shifted due to the star's motion.

How does the Doppler Effect apply to light?

It causes the light from objects moving towards us to appear blue-shifted and light from objects moving away to appear red-shifted.

What does the observation of red-shifted light from galaxies imply about the motion of the Universe?

It implies that the entire Universe is expanding, with galaxies moving away from each other.

What is the relationship between the speed of galaxies and their distance from us?

The further away a galaxy is, the faster it is moving away from us, consistent with the expansion of the Universe.

What is the most likely explanation for the observed red-shift in galaxies?

The whole Universe is expanding, supporting the Big Bang theory.

What does the term 'expanding Universe' refer to?

The concept that all galaxies are moving away from each other, indicating that the Universe is growing larger over time.

What kind of evidence do scientists use to support the Big Bang theory?

Observations of red-shifted galaxies and the detection of cosmic microwave background radiation.

What does the term 'absorption spectrum' refer to?

The spectrum of light that shows dark lines where specific wavelengths have been absorbed by elements in a star.

Why is the Big Bang theory considered a significant scientific theory?

It provides a comprehensive explanation for the origin and evolution of the Universe based on extensive observational evidence.

What does the observation of the cosmic microwave background radiation suggest?

It suggests that the heat from the Big Bang is still present and detectable throughout the Universe.

When refraction occurs

Angle of incidence is smaller than critical angle

When reflection occurs

Angle of incidence is greater than critical angle

Uses of total internal reflection

Transferring information through fiber optic cables

What type of wave are sound waves?

Longitudinal waves

What category of wave do sound waves belong to?

Mechanical waves

Why are sound waves not electromagnetic waves?

They require a medium to travel through

Why are sound waves not ionising radiation?

They do not have enough energy to remove electrons

How do sound waves transfer energy?

Through vibrations in a medium

What direction do particles move in a sound wave?

Parallel to the direction of wave travel

What is the wave speed formula?

Wave speed = frequency × wavelength

What is the unit of wave speed?

metres per second (m/s)

What is the unit of frequency?

hertz (Hz)

What is the unit of wavelength?

metres (m)

What is frequency?

Number of waves passing a point per second

What is wavelength?

Distance between two corresponding points on a wave

What is amplitude?

Maximum displacement from equilibrium