Waves Flashcards
What are waves and what do they do?
Waves are vibrations that transfer energy from a source, outwards, to the surrounding area and sometimes can be used to transfer information, such as sound or TV signals
What three things can waves be described by?
- amplitude
- wavelength
- frequency
The speed of a wave can be calculated from its…..
Frequency and wavelength
Some waves must travel through a substance. Describe this substance and the type of waves that must do this…
- the substance is known as ‘the medium’
- it can be a solid, liquid or gas
- sound waves and seismic waves are like this
- the medium vibrates as the waves travel through it
What kinds of waves do not HAVE to travel through a medium and how does this work?
- visible light
- infrared Rays
- microwaves
- other types of electromagnetic radiation
- as they travel through empty space electrical or magnetic fields vibrate
Describe the characteristics of transverse waves…
- light and other types of electromagnetic radiation are transverse waves
- water waves and S waves (a type of seismic wave) are also transverse waves
- in transverse waves the vibrations are at right angles to the direction of travel
Describe the characteristics of longitudinal waves…
- sound waves and waves in a stretched spring
- P waves (relatively fast moving longitudinal seismic waves that travel through liquids and solids)
- the vibrations are along the same direction as the direction of travel
Describe what is meant by the amplitude of a wave…
- the amplitude is how big the wave is
- as waves travel, they set up patterns of disturbance. The amplitude of a wave is its maximum disturbance from its undisturbed position
- in the case of sound, we call it loudness because the bigger the amplitude the louder a sound is, and vice versa
NOTE!! The amplitude is NOT the distance between the top and bottom of a wave
What is meant by the wavelength of a wave?
The distance between a point on one wave and the same point on the next wave. It is generally easiest to measure this from the crest of one wave to the crest of the next, but it doesn’t matter as long as it is the same point in each wave
Describe the frequency of a wave…
- the number of waves produced by a source each second and the number of waves that pass a certain point each second
- it is measured in Hertz (Hz)
- the number of times the wave wobbles up and down in each and every second
When waves have very high frequencies what measurements may be used?
- kilohertz (kHz)
- megahertz (MHz)
- gigahertz (GHz)
How do you calculate the speed of a wave?
Wave speed is related to its frequency and wavelength as follows:
Wave speed (m/s) = frequency (hertz) x wavelength (metres)
What famous toy is often used to demonstrate the actions of longitudinal waves, and how?
- the slinky
- one end of the slinky is pushed backwards and forwards
- this causes sections of the spring to bunch up (compressions)
- and sections of the spring to stretch out (rarefactions)
- these points of bunching and stretching look as if they are travelling down the length of the spring from the hand of the person doing the moving backwards and forwards
What kind of waves are water waves? Explain why and how…
- transverse waves
- if a ripple on a pond passes a fishing float, the float will only move up and down; it will not move in the direction of the ripple’s movement
- it is called transverse because this means across or sideways
- the movements that are caused are perpendicular to the direction of travel of the wave
What are the four main factors of a light wave?
- transverse
- does not need a medium
- very fast at 300,000,000 m/s
- deteriorates over a distance
Describe the geocentric model of the solar system…
- put forward by the Greek astronomer Ptolemy (c90 - 168AD)
- used measurements of the sky to create the model which had the earth at the centre
- it was not until the 18th century that Nicolaus Copernicus came up with a different model
Describe the heliocentric model of the solar system…
- put forward by Nicolas Copernicus (1473 - 1543)
- has the sun at the centre of the universe
- it was based on observations with the telescope, work pioneered by the Italian astronomer Galileo Galilei (1564 - 1642)
- did not include Uranus, Neptune or Pluto due to lack of power in telescopes at the time
List some significant points about the astronomer Galileo…
- lived 1564-1642
- was an astronomer working at a time when all scientists believed the earth was the centre of the universe
- using the newly invented telescope he discovered that Jupiter had four moons orbiting it, showing the geocentric model of the solar system must be wrong
- ## his findings put him into conflict with the Catholic Church and he spent a lot of his life under house arrest as a result of his beliefs
What is meant by wave speed?
The time it takes for the wave to come from the origin to the destination
What is meant by the period of a wave?
- the time taken for one complete cycle of oscillation
- high frequency means a small period and vice versa
What is a cathode ray oscilloscope?
- a device that gives a voltage against time graph. The voltage appears on the vertical axis and the time on the horizontal
- they are the only measuring instrument that can show us the way an AC voltage is changing
How do you calculate the period of a wave?
frequency in Hz = 1 / time period in s
Why would a DC supply only give a horizontal line?
Because it’s voltage value never changes
What is interference?
When two waves meet and their effects are added together
What is constructive interference?
- when two waves meet and arrive in step, they reinforce each other to give a wave of greater amplitude
- this is called constructive interference
What is destructive interference?
- when two waves meet and arrive out of step they cancel out
- this is destructive interference
How do fluorescent tubes glow?
- Mercury vapour inside the tube gives off UV rays when a current is passed through it
- when the UV light strikes the fluorescent powder which is coating the tube, white light is given out
Describe how digital signals work within communications…
- to send a message using a digital signal, the information is converted into a sequence of numbers called a binary code
- the code uses just two digits (0 and 1) rather than the 10 we normally use
- these numbers are then converted into a series of electrical pulses that are sent down the telephone lines
How do analogue signals work with regards to communications?
- information is converted into voltages or currents that vary continuously
- for example a microphone can convert sound waves into electrical waves, then an amplifier will amplify these waves and feed them into a loudspeaker which will emit them as sound waves
List some advantages of digital signals…
- all signals become weaker during transmission and need to be amplified or regenerated. Regeneration of digital signals creates a clean, accurate copy of the original, while amplified analogue signals also amplify any accompanying noise.
- digital systems are easier to design and build
- digital systems deal with data that is easy to process
What is an object that emits its own light called?
A luminous object
What is an object that does not emit light called, and how can we see it?
- a non-luminous object
- it is visible because of the light it reflects
In a vacuum and in air, light travels at around 300,000,000 m/s. What speed does it travel through water?
Around 200,000,000 m/s
