Chapter 4 Mock Flashcards
What do waves do
Transfer energy and information without transferring matter
What happens when a light wave goes through something more dense
Slows down and bends towards normal
What happens to a light wave when it goes through something less dense
It speeds up and bends away from the normal
How to measure velocity of air
Someone stand for away and make a loud banging noise and time how long it takes for someone in another place to hear it
Speed of sound
340
What is the wave length
The distance between a point on one wage and the same point on the next wave- often easiest to measure from Crest to crest
What is frequency in terms of waves
The number of waves produced by a source each second or the number of waves that pass a certain point each second
Measured In hertz
What is the period of a wave
The time it takes to complete one full oscillation
What is the amplitude of a wave
Maximum disturbance from its undisturbed position
From centre line to top of crest or bottom of trough
What is the velocity of a wave
Number of wave passing a given point at a given time
What is a longitudinal/ P wave give characteristics and example
Can travel through liquids and solids&;gasses
Vibrations In same direction (parallel) as the direction of travel
Seismic
Fast
E.G. SOUND
What is a transverse/ S wave give characteristics and give me an example
Vibrations are at right angles to the direction of travel
Slow
Travel through solids only
E.G. ALL THE WAVES IN ELECTROMAGNETIC SPECTRUM AND WATER
Equation for wave speed
v = f x λ
What does this symbol stand for - λ
Wave length
It’s called a lambda
What is sound with frequencies of greater than 20,000 hertz known as
Ultrasound
What is Sound with frequencies less than 20 hertz know as
Infrasound
What is the range of frequencies humans can hear
15-18,000 hertz
How to measure velocity of sound in air
2 people apart and a certain distance
One bangs two blocks together
As soon as you see the blocks hit each other start the stop watch and stop it when u hear a sound
Calculate the speed by dividing the distance and the time
To eliminate human error use a computer timed method with two sound activated switches
Practical to measure velocity of ripples on water surface
Use a ripple tank and fasten a ruler on the sides so you can see markings above water level. Put a sheet of white paper underneath, reflection of water on sheet makes easier for counting
Count how many waves formed in 10s
Look at waves against ruler to estimate wave lengths of waves, to make it more accurate take a photo of waves with ruler in.
Mark 2 points on the edge of the ripple tank and measure the distance and use a stop watch to find out how long it takes from a wave to go from one mark to the other
How to calculate depth or distance from time and wave velocity
Use the distance = speed x time triangle and double answer if it’s asking for there and back
What are the effects of reflection
Sound and light waves reflect from surfaces. When they reflect they obey the law of reflection (the angle of incidence equals the angle of reflection)
Smooth surfaces eg mirrors are good clear specular reflectors whereas rough surfaces scatter sound and light in all directions by disuse reflection.
What are the effects of refraction
Sound and light waves change speed when they pass across the boundary between 2 substances with different densities such as air and glass. This causes them to change direction and this effect is called refraction.
What happens in refraction if the boundary is at an angle of 90
The line carries straight on
What are the effects of transmission
Energy in a wave is transmitted through a pulse in wave from a less dense medium and at the boundary moves to a more dense medium. They move through materials without being absorbed
Eg- radio waves are used to transmit television and radio programs
What are the effects of absorption
Absorption transfers its energy to the material it penetrates
Eg- sand is hot as it absorbs electromagnetic waves from the sun
Absorption of light to see colour
What colour will an object be if all wavelengths are reflected equally
White
What colour will the object he if all the wavelengths are absorbed
Black
How does human ear receive sound
The eardrum is connected to a hammer, movements and vibrations of war drum will set the hammer, anvil and stirrup into motion at the same frequency of the sound wave. The three tiny bones of the middle ear act as levers to amplify vibrations of the sound wave.
Uses of ultrasound in ships and submarines
Called Sonar- used on ships and submarines to detect fish or seabed. A pulse of ultrasound is sent out from the ship, it bounces off the object and echo is detected, the Tim taken for wave to travel indicates the depth of the object
Uses of ultrasound In foetal scanning
Ultrasound energy being reflected each time it passes from one material to another(boundaries between different tissues and organs) every time it reflects an image is created On a screen. A watery jelly is used as the jelly reflects more sound so u have a clearer view, whereas the air would reflect the sound.
Why shouldn’t their be any air bubbles in the jelly of an ultrasound
So none of the sound is reflected in the air which give an inaccurate view
Why do metal objects show up in ultrasound scans
They are dense so reflect a picture
Why are ultrasound scans used instead of x rays for scan of a baby
Don’t damage living cells
Procure image of soft tissue
Another example of a medical use of an ultrasound
Breaking down kidney stone with Hugh powered ultrasound waves. The stones vibrate until the shake themselves apart and are then easily passed out of the body via the urethra
Uses of infrasound
Communicating over long distances- elephant herds
Detecting volcanic eruptions
Tracking passage if meteors
Use of ultra sound for exploring the earths core
When seismic waves pass through earth they refract or bend.
Speed of seismic waves depends on densities.
Core has a depth of 2900km and is composed of iron. We know it exists because it refracts seismic waves- creating a shadow zone.
Outer part of core = liquid as seismic waves don’t pass through it
What happens when sound waves (p waves) travel through materials
Speed up in denser material and bend away from the normal
What happens to wavelength in denser and less dense material
Dense=The wavelength increases
Less dense= The wavelength decreases (shorter)
What happens to light waves (s waves) as they travel through materials
The slow down in dense materials and bends towards normal
What is total Internal reflection
In optical fibres (thin high quality glass)
What is total internal reflection
Found in optical fibres (small thin glass) when light tries to move from glass to air at a greater angle than the critical angle the refracted ray cannot escape the glass. Total internal reflection occurs inside class and is called total because all the light must be reflected as it travels down rod/fibre
Uses of optical fibres
Endoscopes- surgeons see inside patient
They carry enormous amounts of information as pulses as Light - more info than copper cable tv lines.
High speed communications, e.g. Cable tv and high speed broadband services.
Why do we use jelly on stomach of pregnant women when using an ultrasound
Allows scanner to move around and acts as a medium for the waves to reflect into, more sound will be transmitted
