P12 and P13 Revision Flashcards
To revise Chapter 12 and 13
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 (equilibrium) 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 waves cant 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 induce 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
What is the typical wavelength of an X-ray?
1x10^-10 m
How does infrared and visible light travel through fibre optic cables?
Total internal reflection
Which parts of the electromagnetic spectrum are ionising
Gamma, X-Rays and part of Ultraviolet
