GCSE Physics- Waves (Y10)

What are the 2 types of wave?

• Transverse

• Longitudinal

What kind of wave are the ripples on a water surface?

transverse

What makes something a transverse wave?

Oscillations are perpendicular to the direction of the energy transfer / wave travel

What makes something a longitudinal wave?

• Oscillations are parallel to the direction of energy transfer / wave travel

• Show areas of compression (where the particles are closest together) and rarefaction (where the particles are furthest apart)

What is an example of a longitudinal wave?

Sound waves travelling through air

What is the amplitude of a wave?

• The maximum displacement of a point on the wave away from its undisturbed position

• (On transverse wave, measure height from undisturbed middle line or half of the height from trough to peak)

What does higher amplitude of a wave mean?

The bigger the amplitude of the waves, the more energy the waves carry

What is the wavelength of a wave?

• The distance from a point on one wave to the equivalent point on the adjacent wave

• (So the distance from one peak/trough/compression to the next)

What is the frequency of a wave?

• The number of waves passing a point each second

• (Also the number of oscillations per second)

• Measured in Hertz (Hz)

What happens to the wavelength when the frequency increases?

decreases

What is the period of a wave?

The time taken for one whole wave to pass a point

What is wave speed?

The speed at which the energy is transferred (or the wave moves) through the medium

How would you measure the speed of sound waves in air?

• Measure time between seeing and hearing loud far away action

• Speed = distance / time

How would you measure the speed of ripples on a water surface?

• Take picture of ripple tank next to ruler to find wavelength

• Count number of waves that pass a point in 10 secs (can be on slow motion video with stopwatch if needed) then divide by 10 to find frequency

• wave speed = frequency x wavelength

How would you illustrate the reflection of a wave using a ray diagram?

1. Draw a normal (a dashed line 90° from the surface it's reflecting off)

2. Measure and label the angle of incidence (angle between normal and ray that hasn't yet been reflected)

3. Draw and label reflected ray - the angle of incidence = the angle of reflection (from the normal, but on the other side of it)

4. Draw arrows on all rays to show the direction of energy transfer

Can sound waves travel through all mediums?

• Yes

  • Can travel through solids causing vibrations in the solid

How do we hear?

Sound waves cause the ear drum and other parts of the ear to vibrate which causes the sensation of sound

Why is human hearing restricted?

The conversion of sound waves to vibrations as solids works over a limited frequency range

What happens to our perception of a sound wave when we increase its amplitude?

Its volume increases / it gets louder

What happens to our perception of a sound wave when we increase its frequency?

It gets higher (pitch changes)

What is the range of normal human hearing?

20 Hz to 20 kHz

How do ultrasound waves work?

• Have higher frequency than our upper limit of hearing

• Partially reflected when they meet a boundary between 2 different media

• The time taken for the reflections to reach a detector can be used to determine how far away such a boundary is

• This allows ultrasound waves to be used for both medical and industrial imaging

What are seismic waves?

Waves produced by earthquakes

What are P-waves?

• Longitudinal seismic waves

• Travel at different speeds through solids and liquids

• Detected on the opposite side of Earth

• Refractions between layers cause 2 shadow zones where no P-waves are detected. The size and positions of these indicate there's a solid inner core

What are S-waves?

• Transverse seismic waves

• Can ONLY travel through solids

• Slower than P-waves

• Aren't detected on the other side of the world which suggests the mantle is solid but the outer core must be liquid

What is one use of echo sounding using high frequency sound waves?

Detecting objects in deep water and measuring water depth

What are electromagnetic waves?

Transverse waves that transfer energy from the source of the waves to an absorber

What is the difference between the speeds of the different waves in the electromagnetic spectrum?

All types of electromagnetic wave travel at the same velocity through a vacuum (space) or air

How are the waves in the electromagnetic spectrum grouped?

• Wavelength

• Frequency

What is the electromagnetic spectrum from long to short wavelength (or low to high frequency)?

• Radio

• Microwave

• Infrared

• Visible light (red to violet)

• Ultraviolet

• X-rays

• Gamma rays

Acronym for electromagnetic spectrum

Rich Martians Invaded Venus Using X-Ray Gadgets

What parts of the electromagnetic spectrum do our eyes detect?

Visible light so a limited range of electromagnetic waves

What are the 4 things that may happen to waves at the boundary between 2 materials?

• Absorb

• Transmit

• Reflect

• Refract

Why does refraction happen?

Due to the difference in velocity of the waves in different substances

How do you know which way a wave will refract?

When a wave travels from a fast to slow medium (e.g air to glass) it will bend towards the normal at the boundary and vice-versa

How do you illustrate the refraction of waves using a ray diagram?

1. Draw refracted ray refracting in correct direction

2. If needed, the angle of refraction is between the refracted ray and the normal (dashed line 90° to boundary)

3. If going back to original medium, the transmitted ray (ray that comes out of medium after refraction) will be refracted the same amount as the incident ray was but in the opposite direction so will be parallel to incident ray

How may radio waves be produced?

by oscillations in electrical circuits

What may radio waves do when they're absorbed?

• May create an alternating current with the same frequency as the radio wave itself

• So radio waves can themselves induce oscillations in an electrical circuit

What can changes in atoms and the nuclei of atoms result in?

• Electromagnetic waves being generated or absorbed over a wide frequency range

• Gamma rays originate from changes in the nucleus of an atom

Which waves can have a hazardous effect on human body tissue?

• Ultraviolet waves

• X-rays

• Gamma rays

What does the effect of hazardous waves on the body depend on?

• Type of radiation

• Radiation dose

What is radiation dose?

• A measure of the risk of harm resulting from an exposure of the body to the radiation

• Measured in sieverts (Sv)

How can ultraviolet waves be dangerous?

• Can cause skin to age prematurely

• Can increase risk of skin cancer

How can X-rays and gamma rays be dangerous?

• Ionising radiation

• Can cause the mutation of genes and cancer

What are some uses of radio waves?

Television and radio

What are some uses of microwaves?

• Satellite communications

• Cooking food

What are some uses of infrared?

• Electrical heaters

• Cooking food

• Infrared cameras

What are some uses of visible light?

Fibre optic communications

What are some uses of ultraviolet?

• Energy efficient lamps

• Sun tanning

What are some uses of X-rays and gamma rays?

Medical imaging and treatments

How does a lens form an image?

By refracting light

What happens in a convex lens?

Parallel rays of light are brought to a focus at the principal focus (converging)

What is focal length?

The distance from the lens to the principal focus

What type of image can be produced by a convex lens?

Real or virtual, inverted or upright, magnified or diminished or same size

What type of image can be produced by a concave lens?

Only virtual, upright, diminished

How do you draw a ray diagram for a convex lens?

1. Draw one ray going straight to lens from top of image, then down through the focal point

2. Draw another ray going straight through centre line

3. If they overlap, draw arrow from centre line to place where they do. This is image. Downwards arrow = inverted.

   • If lines don't cross over, follow them the other way to create a virtual image

How do you draw a ray diagram for a concave lens?

1. Draw one ray going straight to lens from top of image, then line up ruler with focal point on same side as image and point where ray met lens and draw a virtual ray.

2. Draw another ray going straight through centre line

3. Virtual image is where they overlap.

What is the magnification equation?

• magnification = image height / object height

• the units of height should be the same as each other

How can a convex lens be represented on a ray diagram?

How can a concave lens be represented on a ray diagram?

Why do we see different colours within the visible light spectrum?

Each colour has its own narrow band of wavelength and frequency

What are the primary colours of light?

red, green, blue

Which colour has the highest frequency and shortest wavelength?

Violet

Which colour has the lowest frequency and longest wavelength?

Red

What is specular reflection?

Reflection from a smooth surface in a single direction

What is diffuse reflection?

Reflection from a rough surface which causes scattering

How do colour filters work?

By absorbing certain wavelengths (colours) and transmitting other wavelengths (colours)

How is the colour of an opaque object determined?

• By which wavelengths of light are most strongly reflected

• Wavelengths that are not reflected are absorbed

• If all wavelengths are reflected equally the object appears white

• If all wavelengths are absorbed the object appears black

What do you call objects that transmit light?

Transparent or translucent

What emits infrared radiation?

• All bodies, no matter what temperature, emit and absorb infrared radiation

• The hotter the body, the more infrared radiation it radiates in a given time

What is a perfect black body?

• An object that absorbs all of the radiation incident on it

• Does not reflect or transmit any radiation

• Since a good absorber is also a good emitter, a perfect black body would be the best possible emitter

What determines how much radiation a body (object) emits?

• All bodies emit radiation

• The intensity and wavelength distribution of any emission depends on the temperature of the body

When would the temperature of a body increase?

• A body at constant temperature is absorbing radiation at the same rate as it is emitting radiation

• The temperature of a body increases when the body absorbs radiation faster than it emits radiation

What are some factors affecting the temperature of the Earth?

• The rates of absorption and emission of radiation

• Reflection of radiation into space

G (prefix)

Giga, 10⁹

M (prefix)

Mega, 10⁶

k (prefix)

kilo 10³

c (prefix)

centi 10^-2

m (prefix)

milli 10^-3

μ (prefix)

micro 10^-6

n (prefix)

nano 10^-9

What are the units for the period of a wave?

seconds (s)

What are the units for frequency?

Hertz (Hz)

What are the units for wave speed?

m/s

What are the units for wavelength?

m