Waves

Question 0

What are waves and what do they do?

Answer 0

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

Question 1

What three things can waves be described by?

Answer 1

• amplitude
• wavelength
• frequency

Question 2

The speed of a wave can be calculated from its…..

Answer 2

Frequency and wavelength

Question 3

Some waves must travel through a substance. Describe this substance and the type of waves that must do this…

Answer 3

• 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

Question 4

What kinds of waves do not HAVE to travel through a medium and how does this work?

Answer 4

• visible light
• infrared Rays
• microwaves
• other types of electromagnetic radiation
• as they travel through empty space electrical or magnetic fields vibrate

Question 5

Describe the characteristics of transverse waves…

Answer 5

• 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

Question 6

Describe the characteristics of longitudinal waves…

Answer 6

• 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

Question 7

Describe what is meant by the amplitude of a wave…

Answer 7

• 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

Question 8

What is meant by the wavelength of a wave?

Answer 8

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

Question 9

Describe the frequency of a wave…

Answer 9

• 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

Question 10

When waves have very high frequencies what measurements may be used?

Answer 10

• kilohertz (kHz)
• megahertz (MHz)
• gigahertz (GHz)

Question 11

How do you calculate the speed of a wave?

Answer 11

Wave speed is related to its frequency and wavelength as follows:

Wave speed (m/s) = frequency (hertz) x wavelength (metres)

Question 12

What famous toy is often used to demonstrate the actions of longitudinal waves, and how?

Answer 12

• 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

Question 13

What kind of waves are water waves? Explain why and how…

Answer 13

• 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

Question 14

What are the four main factors of a light wave?

Answer 14

• transverse
• does not need a medium
• very fast at 300,000,000 m/s
• deteriorates over a distance

Question 15

Describe the geocentric model of the solar system…

Answer 15

• 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

Question 16

Describe the heliocentric model of the solar system…

Answer 16

• 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

Question 17

List some significant points about the astronomer Galileo…

Answer 17

• 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

Question 18

What is meant by wave speed?

Answer 18

The time it takes for the wave to come from the origin to the destination

Question 19

What is meant by the period of a wave?

Answer 19

• the time taken for one complete cycle of oscillation

- high frequency means a small period and vice versa

Question 20

What is a cathode ray oscilloscope?

Answer 20

• 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

Question 21

How do you calculate the period of a wave?

Answer 21

frequency in Hz = 1 / time period in s

Question 22

Why would a DC supply only give a horizontal line?

Answer 22

Because it’s voltage value never changes

Question 23

What is interference?

Answer 23

When two waves meet and their effects are added together

Question 24

What is constructive interference?

Answer 24

- when two waves meet and arrive in step, they reinforce each other to give a wave of greater amplitude - this is called constructive interference

Question 25

What is destructive interference?

Answer 25

- when two waves meet and arrive out of step they cancel out | - this is destructive interference

Question 27

How do fluorescent tubes glow?

Answer 27

- 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

Question 28

Describe how digital signals work within communications...

Answer 28

- 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

Question 29

How do analogue signals work with regards to communications?

Answer 29

- 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

Question 30

List some advantages of digital signals...

Answer 30

- 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

Question 31

What is an object that emits its own light called?

Answer 31

A luminous object

Question 32

What is an object that does not emit light called, and how can we see it?

Answer 32

- a non-luminous object | - it is visible because of the light it reflects

Question 33

In a vacuum and in air, light travels at around 300,000,000 m/s. What speed does it travel through water?

Answer 33

Around 200,000,000 m/s