P2 - Waves Flashcards
What are the different parts of a wave called?
Amplitude = from middle to top of wave Crest = top of a wave Trough = bottom of a wave Wavelength = distance from crest to crest or tough to trough
What is the equation for time period and frequency
Time period (s) = 1/frequency (Hz)
Define transverse waves
The oscillations of the wave go up and down and are perpendicular to the direction of energy transfer.
Examples: electromagnetic waves, ripples and waves in water
Define longitudinal waves
The oscillations are parallel to the direction of energy transfer.
Examples: sound waves, shock waves
What is the equation for wave speed?
Wave speed (m/s) = frequency (Hz) x wavelength (m)
What can you use oscilloscopes for?
To find the wave;engage pf sound waves generated between two microphones
What are the three things that can happen when a wave arrives at a boundary between two different materials?
They can either be:
- Absorbed = transferred to the material’s energy stores
- Transmitted = carry on travelling through
- Reflected
How do you draw a simple ray diagram?
- Draw the line for the object the Ray is being reflected onto (boundary)
- the normal is 90 degrees from the boundary and touches at the point of incidence
- The incoming ray touched the point of incidence
- The reflected ray comes out of the point of incidence
- the angle of incidence is between the incoming ray and the normal
- the angle of refraction is between the reflected ray and the normal
- the angle of incidence and the nag,e of refraction are both equal
Define specular reflection
When a wave is reflected in a single direction by a smooth surface
Define diffuse reflection
When a wave is reflected by a touch surface so the reflected rays are scattered in lots of different directions. Happens because the normal is different for each incoming ray meaning the angle of incidence is different to each Ray.
What happens when a wave crosses a boundary between materials at an angle?
It changes direction and is refracted. If the material is denser the wave travels through it slower and will bend towards the normal. If the material is less denser then the wave will speed up and bend away from the normal. The wavelength changes but the frequency stays the same.
How do you draw a ray diagram for a refracted light ray?
- Draw the boundary and the normal
- Draw the incidence ray (if given use protractor to draw)
- if the second material is denser than the first the refracted ray will bend towards the normal
- This means the angle of refraction will be smaller than the angle of incidence
- If the second material is less dense than the first then the opposite will happen and the angle of refraction will be bigger.
Describe the investigating light practical
Equipment: glass block, ray box, ruler, protractor, pencil
- Shine ray of light using ray box into the middle of the glass block at an angle (this is the incident ray)
- Mark where the light comes out of the glass block on the other side, and trace the incident ray
- Remove the block and use a ruler to join up the incident and refracted ray
- Draw the normal at the point where the light ray entered the block
- Use a protractor to measure the angle of incidence and angle of refraction
- You can repeat at different incident angles or change the material so you have different densities affecting the angle of refraction.
What is the order of the electromagnetic spectrum
Radio waves Microwaves Infrared radiation Visible light Ultraviolet X-rays Gamma rays
Define EM wave
Transverse waves that transfer energy from a source to an absorber. They travel at the same speed through air or a vacuum. They are all used for different purposes due to their different wave lengths.
What are radio waves used for?
They have wavelengths longer than 10cm so they are used for communications.
- Long wave radio (wavelengths of 1-10km)
- Short wave radio signals (wavelengths of 10-100m)
- Bluetooth (uses short wave radio to send data without wires)
- Medium wave signals (reflect from the ionosphere)
- TV and FM radio (very short wavelengths)
What are microwaves used for?
- Communication to and from satellites (including TV and satellite phones)
- Microwave ovens (absorbed by water molecules in food causing it to heat up)
What is infrared radiation used for?
Infrared is given out by all hot objects
- Infrared cameras (detect IR radiation and monitor temperature)
- Toasters
- Electric heaters
What is visible light used for?
Fibre optic cables use visible light to transmit data
What is ultraviolet radiation used for?
- Fluorescent lights (generate UV and re-emit as visible light)
- Security pens (mark property with your name can only be seen under UV light)
- Produced by the sun and gives you a suntan
- Tanning salons with UV lamps (gives artificial suntan but overexposure is dangerous)
What are x-rays use for?
- X-ray photographs (amount of radiation absorbed gives x-ray image, does not pass through bones or metal)
- X-rays used in radiotherapy to treat those with cancer (directed towards cancer cells)
What are gamma rays used for?
- Radiotherapy to treat cancer patients
- Medical tracer (gamma-emitting source injected into patient)
What EM radiation is harmful to people?
High frequency waves transfer lots of energy and so can cause lots of damage.
- UV radiation damages surface of cells leading to sunburn, blindness, and skin cancer
- X-rays and gamma rays are ionising radiation (they can knock electrons off of atoms) which can cause gene mutation, cell destruction, and cancer.
Define convex lens
Bulges outwards, causes rays of light parallel to the axis to converge at the principal focus. When drawn it is parallel rays passing through the lens and then all converge after they have passed through.
Define concave lens
Caves inwards, causes parallel rays of light to spread out. The principal focus is where the rays hitting the lens parallel to the axis appear to all come from meaning they can all be traced back to a point behind the lens.
What are the three rules for refraction in a convex lens?
- Incident ray parallel to axis refracts through lens and passes through principal focus on other side
- Incident ray passing through principal focus refracts through lens and travels parallel to axis
- Incident ray passing through centre of lens carries on in same direction.
What are the three rules of a concave lens?
- Incident ray parallel to axis refracts through lens and travels in line with principal focus
- Incident ray passing through lens towards principle focus refracted through lens and travels parallel to axis
- Incident ray passing through centre of lens carries on in same direction
How do lenses produce real images?
The light from an object comes together to form an image on a screen.
Example: image formed in retina of eye
How do lenses produce virtual images?
The rays diverge so the light appears to be coming from a completely different place.
Example: mirror
How do you draw ray diagrams for a convex lens?
- Draw incident ray going from top of object to lens parallel to axis
- Draw another ray from top of object through middle of lens (where the axis meet)
- Draw line from incident ray to principle focus on other side of lens
- Where the two lines meet is where the image is formed
How do you draw ray diagrams for a concave lens?
- Draw incident ray from top of object to lens parallel to axis of lens.
- Draw ray from top of object through middle of lens
- Draw dotted line from principal focus (on the object side) to where the incident ray meets the lens
- Carry on this line beyond the lens but without it being dotted
- Where the ray that passes through the axis meets the line from the principal focus is where the image is.
What kind of lens do magnifying glasses use?
Convex lens to create a virtual image
What type of radiation do all objects absorb and emit?
Infrared radiation
Which is better at absorbing and emitting radiation: Black and Matt or white and shiny?
Black objects and matt objects are better
Define a perfect black body
A perfect black body is an object that absorbs all of the radiation that hits it. None is reflected or transmitted.
How does radiation affect the earth’s temperature?
Day - Lots of radiation (light) is transferred to earth from sun and is absorbed causing increase in temperature
Night - less radiation is absorbed than emitted causing decrease in temperature
What are sound waves?
They are caused by vibrating objects asa series of compressions and rarefactions. It is a longitudinal wave and is fastest in solids. This is because it can vibrate through the particles. It can’t travel in space because there are no particles to move or vibrate in.
What are echoes?
They are just reflected sound waves
Why do sound waves speed up when they enter a denser material?
The wavelength changes but the frequency stays the same so the speed has to increase.
Define ultrasound
Sound with frequencies higher than 20,000 Hz. They are mechanical vibrations that are sound waves beyond the range of human hearing.
What is partial reflection?
When a wave passes from one medium into another, and some is reflected and some is transmitted.
What is ultrasound used for?
- Medical imaging (scanning of foetus)
- Industrial imaging (finding flaw in materials - if there is a crack in an object the wave will be reflected sooner)
- Echo sounding (to find the depth of water they are in to locate objects in deep water)
What kind of waves do earthquakes and explosions cause?
Seismic waves.
What are the two types of seismic waves?
P waves - longitudinal, travel through solids and liquids, faster than S waves
S waves - transverse, can’t travel through liquids or gases, slower than P waves
