VCE Physics 1/2 Unit 1: AOS1

- electromagnetic radiation - thermal energy - Interaction of thermal energy and electromagnetic radiation

What are the key features of mechanical wave that can be identified on a graph?

• amplitude

• wavelength

• frequency

• period

• speed

Wave properties

Amplitude, wavelength, period, and frequency define the characteristics of a wave.

What does amplitude represent?

How intense the sound or light is

What are wavelength and wave speed dependent on?

the medium in which light travels through

Label the parts of reflection in order

incident ray, angle of incidence, normal, angle of reflection, reflected ray

What is specular reflection?

it occurs when light reflects off a smooth surface, where the angle of incidence is equal to the angle of reflection

What is diffuse reflection?

it occurs when light reflects off a rough surface, scattering the light in many directions, and doesn't form a clear image

What is refraction?

the bending of light (change in direction) as it passes from one medium to another, caused by changes in speed

When does refraction occur?

if a light strikes a material at an angle other than 90 degrees, the light bends

light in air is ?

faster

light in water is ?

slower

when light is going from fast → slow

• light bends towards normal

when light is going from slow → fast

• light bends away from normal

Refractive index: n=c/v, what do each of the letters stand for?

n - refractive index c - speed of light in a vacuum v - speed of light in a medium

How to know how much the light bends?

depends on the difference in speed of light in the medium

What is light?

a form of electromagnetic radiation

Low frequency = ?

high wavelength

High frequency = ?

low wavelength

What is total internal refraction?

occurs when the angle of refraction goes past 90°, which means that the surface boundary acts as a mirror and no light gets past. it can only occur when slow → fast

What is the significance of the critical angle in total internal refraction?

critical angle = angle of incidence when the angle of refraction is 90°

What is dispersion?

A part of refraction, is the separation of white light into different colours when it passes through a medium such as water droplets or a prism.

Why does dispersion occur?

different wavelengths of light have different refractive indexes in a given medium

What kind of light waves refract less?

lower frequencies like red

What kind of light waves refract more?

higher frequencies like violet

Name the colours of the rainbow in order of least to most refracted

red, orange, yellow, green, blue, indigo, violet (ROYGBIV)

Light waves bend towards?

cooler air

Why is the sky blue?

As white light hits molecules in the atmosphere, blue refracts the most and scatters across the sky. This blue light bounces from the atmosphere towards our eyes, giving the appearance of a blue sky.

Why is the sky red-orange at sunset?

The Sun is very low in the sky, which means the light has to travel through a thicker amount of atmosphere, causing significant levels of refraction of blue, making it scattered and deflected before it reaches us.

What is chromatic aberration, and what is it caused by?

a type of distortion caused by different frequencies of light being focused at different points due to refraction

How can chromatic aberration be resolved?

• using a lens with longer focal length: decreases the angle at which light is refracted, leading to less refraction overall

• using achromatic lenses, as they are made of different materials with different refractive indices

• taking separate pictures with different coloured filters and combining them to form a single multi-coloured

What are optical fibre cables, and what are they used for?

they make use of total internal refraction to direct light through a cable and are used for sensors, communication, and more.

Which refracts less? Hot or cold air?

Hot air, due to the density of the molecules. Molecules are spread apart when it's hot.

What does the brain assume about light?

light travels in a straight line path

How does refraction affect how we see objects?

when light refracts, it can enter our eyes from a different direction, making objects appear to be located somewhere where they actually aren't

The outer cladding of optical fibre cables have?

a low refractive index

The inner core of optical fibre cables have?

a high refractive index

What is an inferior mirage?

the perceived object (where we think it is) appears below the real object (where it actually is)

Why does an inferior mirage look like water on the ground?

The brain interprets the bent light as a reflection, making the surface appear as if it's covered with water

When does an inferior mirage occur?

when cooler air is over warmer air, causing light to bend upwards, and is usually inverted because of this

What is a superior mirage?

a mirage where the perceived object appears above the real object. They may be inverted or upright.

When does a superior mirage occur?

when warmer air is over cooler air, causing light to bend downward

How do mirages form?

because of refraction and total internal reflection when light bends as it passes through layers of air with different temperatures

What is a wave?

the transfer of energy without the net transfer of matter.

How does energy transfer in a wave?

the oscillation of particles, moving back and forth or up and down around an average position, without net matter transfer.

What is a mechanical wave?

A wave that requires a medium (physical substance) to transmit (carry or transfer) energy

What type of waves are electromagnetic waves?

Transverse waves

What is a wave pulse?

singular wave caused by one initial disturbance, carries energy away from source because it travels away

What is a periodic wave?

a wave that repeats at regular time intervals, transferring energy without net matter transfer. It is caused by the oscillation of particles within the medium, which is caused by the continuous vibration of the source.

What is the source of any mechanical wave?

vibration

What is a transverse wave?

Waves in which the particles in a medium vibrate up and down in a perpendicular/transverse direction to the motion of the wave energy.

What is a crest?

the maximum positive point of displacement of particles in a wave

What is a trough?

the maximum negative point of displacement of particles in a wave

What is a longitudinal wave?

a wave where the vibration of the particles is parallel to/same direction as the direction of the energy flow

What is a compression, and what does it correspond to in a transverse wave?

where the coils come together, corresponds to crest because it's an area of high pressure --> particles are close together

What is a rarefaction, and what does it correspond to in a transverse wave?

the areas of expansion in the coil, correspons to troughs because the pressure is lower --> particles are spread out

Example of a longitudinal wave?

sound wave! 🎶🎧

What happens to longitudinal waves if the vibration comes from a single point?

the waves spread out spherically

water waves:

in practical situations, transverse and longitudinal waves don't always occur in isolation, Water waves are an example of this, where the surfer moves forward while the water moves elliptically

What is the speed of electromagnetic waves in a vacuum?

The speed of light (c)

Do electromagnetic waves require a medium to travel?

No, they do not require a medium.

What is an example of an electromagnetic wave?

Sunlight

Mechanical wave

-> requires a medium to transmit (carry or transfer) energy

What is a medium?

A physical substance

What shape does a wave take as it moves through a medium?

spreads in the shape of a sine or cosine function as it moves through a medium.

What does a displacement-time graph show?

how the position (displacement) of a particle changes over time as it oscillates around a central position.

Define amplitude

The maximum displacement of a wave from its equilibrium position. a.k.a. the middle of a wave to a trough/crest.

• a particle will move the total distance of twice the amplitude in one cycle

What are the units amplitude?

m

What is wavelength?

The distance between any two successive points in phase.

What does it mean for two particles to be in phase?

They have the same displacement from the average position and are moving in the same direction.

What represents wavelength?

λ (lambda)

What is frequency in a wave?

the number of complete cycles that pass a given point per second. It is measured in hertz (Hz).

How can wave motion be analysed using distance-time graphs?

by comparing multiple displacement-time graphs, you can determine the wave's speed, direction of motion of particles, and direction of the wave.

What is the purpose of a displacement-time graph?

to track the position of one point in time as the wave moves through that point

What are the differences between displacement-distance graphs and displacement-time graphs?

crests, troughs, and amplitude is the same, but wavelength is period in displacement-time

What is the period in a displacement-distance graph?

the time taken for any point on the wave to go through a complete cycle (e.g. from crest to crest). The period of a wave is inversely related to its frequency.

What can a displacement-time graph determine about a wave?

the amplitude, period, and direction of motion of a particular particle

WATCHOUT!!

the displacement-time graph looks very similar to the displacement-distance graph of a transverse wave, so be careful to check the horizontal axis label!!

What letter represents frequency?

f

Formula for period of wave

T=1/f (freq)

Wave equation

𝜆 = 𝑣/𝑓 = 𝑣𝑇, where 𝜆 is wavelength, 𝑣 is velocity, 𝑓 is frequency, and 𝑇 is period.

wavelength is measured in?

m

One wavelength occurs in the time of?

one period 😁😜

What types of waves does the wave equation apply to?

mechanical waves (e.g. water waves, sound waves and seismic waves) or electromagnetic waves (including light waves)

What is the electromagnetic spectrum?

A set of possible wavelengths that visible light is a small part of.

What type of wave is light?

a transverse wave that doesn't need a medium to travel. Like all electromagnetic radiation (EMR), it can travel through a vacuum.

What two fields make up light waves?

Light consists of two perpendicular waves:

• one is an electric field wave

• one is a magnetic field wave

How are the electric and magnetic fields oriented in a light wave?

the electric and magnetic fields are perpendicular to both eachother and the direction of radiation propagation

What is wave propagation?

the movement or spreading of a wave through a medium or a space. Mechanical waves require a medium, whilst electromagnetic waves can propagate through a vacuum or medium.

What is the difference of the wave equation applied to EMR?

The wave equation also applies to EMR, however, the speed of light is always constant in a vacuum, regardless of the speed of the source/observer, so it has it's own constant.

The wave equation for EMR and what it stands for

λ=c/f c= speed of light 3.0x10^8 f= frequency (Hz)

Is the speed of light lower or higher in a medium such as glass and also air?

speed of light in air is not that different from in a vacuum; however, in a medium such as glass, it is much lower

How does Earth's atmosphere affect electromagnetic radiation (EMR)?

Earth's atmosphere blocks many types of EMR, allowing only certain wavelengths to reach the surface.

What part of the atmosphere blocks high-energy EMR?

The ionosphere contains charged particles that block gamma rays & xrays

How is Ultraviolet (UV) absorbed in the atmosphere?

The ozone layer and the nitrogen in the lower atmosphere absorb about 70% of UV radiation, preventing most of reaching earth

Why does visible light pass through the atmosphere?

it is not energetic enough to be absorbed by earth's atmospheric gases

Why does the atmosphere block infrared and microwave radiation?

The atmosphere becomes increasingly opaque in the microwave and infrared bands due to absorption by water vapour

What happens to the atmosphere at even lower energies

The atmosphere appears transparent to shorter wavelengths of low-energy EMR, such as radio waves, allowing them to reach the surface

Can all low-energy EMR reach earth's surface?

No, very long wavelength EMR (some radio waves) cannot penetrate the atmosphere and are blocked

Wave velocity

Determined by the medium through which the wave travels, while frequency is set by the source.

What does the electromagnetic spectrum include?

Includes radio, microwave, infrared, visible, ultraviolet, X-ray, and gamma waves, each with different wavelengths and frequencies.