P2: Waves Flashcards
What are the two types of waves?
Transverse or longitudinal.
How do the particles vibrate in transverse waves?
The particles vibrate at right angles (90°) to the direction of energy transfer.
What are the vibrations in waves known as?
Oscillations.
State some examples of transverse waves.
Water waves, electromagnetic spectrum waves, secondary waves.
Describe the vibration of particles in a longitudinal wave.
The particles vibrate in parallel with the direction of energy transfer.
What are the two types of periods that the longitudinal wave travels through?
Compression and rarefaction
State some examples of longitudinal waves.
Sound waves and seismic primary waves.
What is amplitude?
The maximum displacement of a point on the wave of the undisturbed position.
What is wavelength?
The distance from a point on one wave to the same point on the next. (Crest to crest)
What is frequency?
The number of waves that pass a point each second.
What is the period?
The time is takes for one complete wave oscillation.
What is the equation for wave speed?
Wavespeed = frequency x wavelength.
How can you measure the speed of sound waves?
Using two microphones connected to a computer. Measure the distance between the two, then make a sound. The computer calculates the time is takes for the sound wave to travel from the first microphone to the second.
What can you use to measure the speed of water ripples?
A ripple tank and a light.
What happens when a wave meets a boundary between two different materials?
The wave is either absorbed, transmitted or reflected.
What happens when a wave is absorbed?
Its energy is transferred.
What happens when a wave is transmitted?
It carries on travelling through the material.
What happens when a ray is reflected?
It travels back.
Why can’t sound waves travel through a vacuum?
Because there are no particles to vibrate.
Name the two types of reflection
Specular and diffuse.
What name is given to a reflection from a smooth surface?
Specular reflection.
What name is given to reflection from a rough surface?
Diffuse reflection
What is the correlation between the angle of incidence and the angle of reflection?
They are equal
A light ray travels through air, then a glass block, then air again. Refraction has not occurred. Why?
The incident ray of the light is along the normal (the ray is perpendicular to the glass surface - but do not remember it this way)
Compare sound waves to water waves
Sound waves are longitudinal, faster and have a higher frequency
Water waves are transverse, slower and have a lower frequency
What is displacement in a wave?
The distance that a certain point in the medium has moved from its rest position
What is the peak in a wave?
The highest point above the rest position
What is the trough in a wave?
The lowest point below the rest position
What is rest position in a wave?
The undisturbed position of the particles or fields when they are not vibrating.
How do you measure frequency using a ripple tank?
-Equipment: Stopwatch, slow-mo camera.
-Count the number of waves passing a point over 10 seconds, then divide the answer by 10.
-This is the frequency.
How do you record wavelength using a ripple tank?
-Equipment: Camera, ruler
-Measure the length of a certain amount of waves
-Divide answer by the number of waves, answer is average wavelength.
State one of the hazards, consequences and control measures from a ripple tank RPA.
-Electrical components near water
-Can cause shock and damage to components
-Secure electrical components before adding water taking care not to splash
Describe the structure of a ripple tank.
-A shallow tank of water with a long vibrating wooden rod placed in one side of the tank, connected to a power pack.
-Below the ripple tank is a piece of white paper with a ruler next to it.
-Above the ripple tank is a bright light
What is the practical of waves on a string used to measure?
Used to measure the waves in a solid
Describe the set-up of the “waves on a string” practical.
-Attach a string to a vibration generator and use a 200g hanging mass and pulley to pull the string taut. Place a wooden bridge under the string near the pulley.
-Switch on the vibration generator and adjust the wooden bridge until stationary waves can be clearly observed.
How do you measure the wavelength of waves on a string?
-Measure the length of as many half wavelengths (loops) as possible
-Divide by the number of half wavelengths (loops).
-This is half the wavelength, doubling this gives the wavelength.
How do you measure the frequency of waves on a string?
-The frequency is the frequency of the power supply.
State one of the hazards, consequences and control measures when measuring waves on a string.
-Cord may snap
-Causing damage to eyes
-So wear eye protection/place safety screen
What do electromagnetic waves transfer energy as?
Radiation.
Can electromagnetic waves travel through a vacuum?
Yes
State the order of the light spectrum.
Radiowaves, Microwaves, Infrared Radiation, Visible Light, Ultraviolet Light, X-rays, Gamma Rays.
State the uses of Radiowaves.
Broadcasting television and radio, satellite transmissions.
State the uses of Microwaves.
Cooking food, satellite communications
State the uses of Infrared Light.
Cooking food, heating electrically, optical fibres, thermal imaging cameras.
State the uses of Visible Light.
Illumination, Fibre optic communications.
State the uses of Ultraviolet Light.
Tanning beds, killing bacteria, security marking.
State the uses of X-rays.
Medical imagery, medical treatment.
State the uses of Gamma Rays.
Sterilising food and medical instruments, treatment and detection of cancer.
What type of waves are electromagnetic waves?
Transverse waves.
What are the vibrations or oscillations in electromagnetic waves?
Changes in electrical and magnetic fields perpendicular to the direction of wave travel.
Describe diffuse reflection.
Instead of forming an image, the reflected light is scattered in all directions. This can cause either a distorted image, or no image at all.
What does the density of a material affect in a wave?
The speed that the wave will be transmitted through it.
What type of waves are sound waves?
Longitudinal
What is the pitch like if the frequency of the sound wave is high?
High pitched.
If a sound wave is low pitched, what is the frequency like?
Low.
Describe the volume of a high amplitude sound wave.
Loud.
Describe the volume of a low amplitude sound wave.
Quiet.
What is the range of human hearing?
20Hz to 20,000Hz
What is the frequency of ultrasound waves?
Above 20,000 Hz.
What does ultrasound imaging rely on?
-What happens when ultrasound waves meet the boundary between two different materials.
-When this happens, some of the ultrasound waves are reflected at the boundary
-The time taken for the waves to leave a source and return to a detector is measured
-The depth of the boundary can be determined using the speed of sound in the material and the time taken.
What is echo sounding used for?
Identifying objects, for example measuring water depth.
What is the difference between echo sounding and ultrasound?
-Echo sounding uses sound waves within normal hearing range, and are used to identify objects.
-Ultrasound uses sound waves above human hearing range, and are used to identify internal structures.
Describe the frequencies of the sound waves used in echo sounding.
Within normal human hearing range.
What are seismic waves produced by?
Earthquakes in the Earth’s crust.
What are the two types of seismic waves?
P-Waves and S-Waves.
What type of wave is an S-wave?
Transverse.
What type of wave is a P-wave?
Longitudinal.
Which wave is faster: P-wave or S-wave?
P-wave.
What can P-waves travel through?
Solids and liquids.
What can S-waves travel through?
Solids only.
Compare P-waves and S-waves.
-P-waves are longitudinal, S-waves are transverse.
-P-waves are faster than S-waves
-P-waves can travel through solids and liquids, S-waves can travel through solids only.
Where are S-waves detected on Earth?
NEVER on the opposite side of the Earth that they came from, which suggests that the outer core is a liquid.
Where are P-waves detected on Earth?
Close to where the wave was transmitted, and the opposite side. This is because the waves refract between layers of the Earth so give the waves a generally straight projectory.
What is a lens?
A shaped piece of transparent glass or plastic that refracts light.
What are the two types of lenses?
Convex and concave.
What are lenses used in?
Cameras, telescopes, binoculars, microscopes, corrective glasses.
Describe the shape of a convex lens.
Thicker in the middle than it is at the edges.
What happens to light rays that travel through a convex lens?
Parallel light rays that enter the lens converge and come together at a point called the principal focus.
Describe the shape of a concave lens.
Thinner in the middle than it is at the edges.
What happens to parallel rays when they meet a concave lens?
They diverge and separate, but appear to come from a principle focus on the other side of the lens.
What are the 3 different variations of images a lens can form?
-Upright or inverted
-Magnified or diminished
-Real or virtual
What is a “real” image?
An image that can be projected onto a screen.
What is a virtual image?
An image that appears to come from behind the lens
How do you draw a ray diagram?
1) Draw a ray from the object to the lens that is parallel to the principal axis. Once through the lens, the ray should pass through the principal focus.
2) Draw a ray which passes from the object through the centre of the lens.
What type of lens do cameras and eyes contain?
Convex lenses.
What type of lenses do projectors contain?
Convex lenses
What type of lens do magnifying glasses contain?
Convex lens.
What type of lens is used in peep holes?
Convex lens.
What is magnification?
A measure of the size of an image compared to the size of the object.
Magnification = image height/object height
What is the spectrum of colour? (In the correct order)
Roy G. Biv
Red, Orange,Yellow, Green, Blue, Indigo, Violet
Describe what happens to the wavelengths of light when they hit an opaque green object.
All of the colours on the spectrum of white light are absorbed by the object, apart from green. The green light is reflected and scattered.
Describe what happens when white light passes through an orange filter.
The filter absorbs all the colours on the spectrum of white light, apart from orange. The orange light is transmitted from the filter.
What absorbs and emits infrared radiation?
All objects.
Describe what happens to infrared radiation when an object gets hotter.
More infrared radiation is given out in a given time.
The hotter the body…
-The more infrared radiation it gives out in a given time.
-The greater the proportion of emitted radiation is visible light.
What are the properties of a perfect black body?
-Absorbs all the radiation that falls on it.
-Doesn’t reflect or transmit any radiation.
What are the worst absorbers and emitters of infrared radiation?
White and shiny silvery surfaces.
Describe the method for investigating how the amount of infrared radiation absorbed or radiated by a surface depends on the nature of that surface.
1) Place a Leslie cube on a heat-resistant mat. Fill it, almost to the top, with boiling water and replace the lid.
2) Leave for one minute. This is to enable the surfaces to heat up to the temperature of the water.
3) Use the infrared detector to measure the intensity of infrared radiation emitted from each surface, or the temperature of the surface. Make sure that the detector is the same distance from each surface for each reading.
Describe one of the hazards, consequences and control measures when using a Leslie cube.
Boiling water, can cause scalds. So, pour water slowly, using a funnel if necessary. Do not move the Leslie cube until it has cooled.
If the rate of absorption is greater than the rate of emission, what is happening to the temperature of the body?
It is increasing.
If the rate of absorption is equal to the rate of emission, what is happening to the temperature of the body?
It is constant.
If the rate of absorption is less than the rate of emission, what is happening to the temperature of the body?
It is decreasing.
What do rays in a convex lens do?
Converge.
What do rays in a concave lens do?
Diverge.
What is the name of the point where rays converge?
Focal point.
What is the name of the point where parallel rays converge?
Parallel focus.
Radio waves are produced by __________ in an electric circuit. What one word completes this sentence?
Oscillations
