Waves - Paper 2 Flashcards
To revise waves (paper 2)
What do waves transfer?
Energy
What are the two types of wave?
Transverse and longitudinal
Describe a transverse wave
The vibrations of the wave are perpendicular** to the direction in which **energy is transferred.
Give some examples of transverse waves
Ripples on a water surface
Any wave in the electromagnetic spectrum
S waves
Describe a longitudinal wave
The vibrations of the wave are parallel** to the direction in which **energy is transferred.
Longitudinal waves show areas of compression** and **rarefaction.
Give some examples of longitudinal waves
Sound waves
Ultrasound
P waves
Define amplitude
The amplitude of a wave is the maximum displacement of a point on a wave away from its undisturbed position.
It shows us how much energy a wave has.
Define wavelength
The wavelength of a wave is the distance from a point on one wave to the equivalent point on the adjacent wave. Measured in meters
Define frequency
It is the number of waves that pass a point per second. Measured in hertz (Hz)
Define period (T)
Its the time for one exact wave to pass a point. Measured in seconds
T = 1 / f
State the wave equation with all units
wave speed (m/s) = frequency (Hz)× wavelength (m)
Describe an experiment to find the speed of sound through air
- Measure a distance of 100 m from a wall.
- Hit two blocks together to make a sound and start timing.
- Stop timing when the hear the reflected sound (echo).
- Divide the time recored by 2 as the sound has travelled to the wall and back again
- use the equation Speed = distance / time
Describe a method to measure the speed of ripples on a water surface.
- Set up a ripple tank.
- Find the wavelength by using a ruler to measure across 10 wavelengths.
- Divide the answer by 10 to find 1 wavelength.
- Use a stopwatch and count the number of waves produced in 10 seconds.
- Dived the answer by 10 to find the frequency.
- Use the equation speed = wavelength x frequency
What can happen to waves when they reach a boundary between two materials?
- They can be reflected
- They can be absorbed (this will cause a small temperature rise)
- They can be transmitted (they will pass through)
What is the law of reflection
The angle of incident = angle of reflection for a flat plain mirror.
What is refraction?
When a wave travels from one medium to another and changes direction.
Why does refraction take place?
The change in medium means a change in density which caused a change in speed.
When a substance moves from a more dense to a less dense substance, what is the affect of waves speeds, frequency and wavelength?
- Wave speed - decreases
- Frequency - same
- Wavelength - decreases
When a substance moves from a less dense to a more dense substance, what is the affect of waves speeds, frequency and wavelength?
- Wave speed - increases
- Frequency - same
- Wavelength - increases
When light slows down which direction does it refract?
Towards the normal
When light speeds up which direction does it refract?
Away from the normal
Explain why light refracts as it passes from air into glass?
As light moves from air into glass it slows down.
The edge of the wave front entering the glass first slows down first
Part of the wave front that is still in the air continues at a higher speed causing it to travel further and to change in direction
State the normal human hearing range
From 20 Hz to 20 kHz
How do we detect sound waves?
Within the ear, sound waves cause the ear drum and other parts to vibrate. These vibrations are converting into an electrical signal which is passed onto the brain.
Why do humans have a limited range of frequencies they can detect?
The conversion of sound waves to vibrations of solids works over a limited frequency range. This restricts the limits of human hearing.
What is the effect of a louder sound on the ear drum?
larger vibrations
What is the effect of a higher pitched sound on the ear drum?
Faster vibrations
What is a ultrasound?
Ultrasound waves have a frequency higher than the upper limit of hearing for humans (20000 Hz)
How can ultrasound be used for medical and industrial imaging?
- Ultrasound waves are partially reflected and partially transmitted when they meet a boundary between two different media.
- The time taken for the reflections to return to the detector can be measured
- This can be used to determine how far away such a boundary is. 2 x Distance = speed x time
What are seismic waves
Waves produced by Earthquakes
What type of waves are P-waves?
longitudinal
What type of waves are S-waves?
Transverse
Which earthquake wave scant travel through the liquid core?
S-waves as they are transverse
What is a shadow zone?
An area where no p waves or s waves are detected
What does a shadow zone show us?
There must be a liquid core because:
P waves are refracted at the core mantle boundary
S waves can’t travel through the liquid core
State the waves that make up the electromagnetic spectrum, in order of increasing wavelength
- Radio waves
- Microwaves
- Infrared
- Visible light
- Ultraviolet
- X-rays
- Gamma rays
What do all electromagnetic waves have in common?
- They are all transverse waves
- They can all travel through a vacuum
- They all travel at the speed of light through a vacuum
How are radio waves produced?
By an oscillating electrical current in the transmitter. The frequency of the current will make the frequency of the radiowaves.
What happens when radio waves are absorbed by an aerial?
When radio waves are absorbed they will create an alternating current with the same frequency as the radio wave itself
What are the dangers of ultraviolet waves
- Can age skin prematurely
- Can burn skin which can lead to skin cancer
- Damage eyes which can lead to blindness
What are the dangers of X-rays and gamma rays?
X-rays and gamma rays are ionising radiation.
Low doses can damage DNA and cause cancer
Large doses can kill cells
State some uses of radio waves
television and radio, these waves stay within the earths atmosphere.
State some uses of microwaves
Satellite communications eg mobile phone and satellite TV. Microwaves can travel to space and back.
Cooking food.
State some uses of infrared
electrical heaters, cooking food, infrared cameras
State some uses of visible light
fibre optic communications
State some uses of ultraviolet
energy efficient lamps
sun tanning
security markings
State some uses of X-rays and Gamma rays
medical imaging and cancer treatment.
Describe how x-rays are used for medical imaging
pass through soft tissue
but are absorbed by bone
How does a lens work?
A lens forms an image by refracting light to a focal point
When describing the nature of an image formed the key words to use are?
- Real or virtual
- Magnified or diminished
- Upright or inverted
What are the units of magnification
no units as it is a ratio
In a ray diagram the symbol for a convex lens will be represented by?
A vertical line with arrow heads at each end
In a ray diagram the symbol for a concave lens will be represented by?
A vertical line with inverted arrow heads at each end
For a lens ray diagram label
Principle axis
Focal point
Focal length
Principle axis - hoziontal reference line through the centre of the lens
Focal point - the point where the rays of light are focused
Focal length - the distance from the centre of the lens to the focal point
Desribe the role of a converging lens
It will take parallel rays of light and converge them to a focal point after the lens.
Describe the role of a diverging lens
It will take parallel rays of light and diverge them from a focal point in front of the lens
Desribe how to draw a ray diagram for a converging lens when the object is a large distance from the lens.
Describe the nature of the image
- Draw a ray of light from the top of the object, through the centre of the lens in a straight line
- Draw a ray of light from the top of the object so it is parallel to the principle axis, once it hits the centre of the lens it will be refracted through the focal point
- Where the two rays of light meet draw an arrow and label it the image.
The image will be real, inverted and diminished
Desribe how to draw a ray diagram for a converging lens when the object is a close to the lens.
Describe the nature of the image
Draw a ray of light from the top of the object, through the centre of the lens in a straight line
Draw a ray of light from the top of the object so it is parallel to the principle axis, once it hits the centre of the lens it will be refracted through the focal point
Draw virtaul rays of light with dashed lines to show where the rays of light appear to have trevelled from.
Where the two virtual rays of light meet draw an arrow and label it the image.
The image will be virtaul, upright and magnified
Desribe how to draw a ray diagram for a diverging lens.
Describe the nature of the image
Draw a ray of light from the top of the object, through the centre of the lens in a straight line
Draw a ray of light from the top of the object so it is parallel to the principle axis, once it hits the centre of the lens it will be refracted away from the focal point that is in front of the lens.
Draw virtaul rays of light with dashed lines to show where the rays of light appear to have trevelled from.
Where the two rays of light meet draw an arrow and label it the image.
The nature of the image is virtual, diminished and upright
Describe specular reflection
Reflection from a smooth surface in a single direction is called specular reflection.
Angle of incidence = Angle of relection
Describe diffuse reflection
Reflection from a rough surface causes scattering: this is called diffuse reflection.
Explain how a red filter works
A red filter will allows the red wavelength to be transmitted** whilst the wavelengths of all the other colours will be **absorbed.
Describe how we can see a blue object.
A blue object will reflect** the blue wavelengths into our eyes. All the other wavelengths and colours will be **absorbed.
Describe how we can see a white object.
If all wavelengths are reflected equally the object appears white.
Describe how we can see a black object.
If all wavelengths are absorbed the objects appears black.
Objects that transmit light are called?
transparent or translucent
What is the relationship between the temperature of an object and the amount of infrared radiation it emits?
The hotter the body, the more infrared radiation it radiates in a given time.
Describe a perfect black body
A perfect black body is an object that absorbs all of the radiation incident on it. A black body 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.
How can a body be at a constant temperature?
A body at constant temperature is absorbing radiation at the same rate as it is emitting radiation.
How can the temperature of a body increase?
The temperature of a body increases when the body absorbs radiation faster than it emits radiation.
How can the temperature of a body decrease?
The temperature of a body decreases when the body absorbs radiation slower than it emits radiation.
What factors affect the temperature of the Earth?
The temperature of the Earth depends on many factors including:
- the rates of absorption and emission of radiation,
- reflection of radiation into space.
What surface is the best emitter of infrared radiation?
Matt black surfaces
What surface is the worst emitter of infrared radiation?
Silver (shiny) surfaces
What surface is the best absorber of infrared radiation?
Matt black surfaces
If an object’s temperature is higher, what will happen to the infrared radiation it’s emitting?
Higher temperature -> more infrared radiation emitted in a given time
Describe how to find the speed of waves from the standing waves experiment.
- Record the frequency off the signak generator
- Use a meter ruler to measure the wavelength
- Use the equation speed = frequency x wavelength
What is the relationship between intensity and wavelength for a black body radiator?
- The intensity reaches a maximum for a specific wavelength which depends on the temperature.
- If the temperature increases the intensity of radiation emitted is greater for each wavelength. (e.g. a hotter star will give out more energy).
- If the temperature increases the peak intensity occurs at a lower wavelength. (this is why stars are different colours)
- For lower temperatures the peak intensity occurs over a broader range of wavelength
