The Nature of Waves

Question 1

What is a progressive wave?

Answer 1

-Carries energy from place to another without transferring any material
-The transfer of energy is in the same direction as the wave is travelling
-The source of the energy loses energy

Question 2

How can you recognise when a wave is carrying energy?

Answer 2

-EM waves cause things to heat
-Xrays and gamma rays knock electrons out of their orbits, causing ionisation
-Loud sounds cause large oscillations in air particles which can make things vibrate
-Wave power can be used to generate electricity

Question 3

What is displacement?

Answer 3

-How far a point on the wave has over from its undisturbed position

Question 4

What is amplitude?

Answer 4

-The maximum magnitude of the displacement

Question 5

What is wavelength?

Answer 5

-The length of one whole wave cycle

Question 6

What is a time period?

Answer 6

-The time taken for a whole cycle to complete

Question 7

What is frequency?

Answer 7

-The number of cycles per second passing a given point

Question 8

What is phase and the phase difference?

Answer 8

-A phase is the measurement of the position of a certain point along the wave cycle
-The difference is the amount tone wave lags behind another
-Measured in degrees or radians

Question 9

What is an oscilloscope?

Answer 9

-A cathode ray oscilloscope measured voltage, displayed as voltage over time
-The displayed wave is called a trace
-The screen is split into squares called divisions
-The voltage axis is controlled by the gain dial
-The seconds axis or the timebase, is controlled by the timebase dial

Question 10

How do you alter the timebase?

Answer 10

-If you plug an AC supply into an oscilloscope, you get a trace which goes up and down in a regular pattern, some positive, some negative
-A microphone converts sound waves into electrical signals

Question 11

What is a transverse wave?

Answer 11

-All EM waves, ripples on water or strings
-At right angles to the direction of travel
-Give a sine wave
-If the displacement is greater than behind the point, the particle will have to move up

Question 12

What is a longitudinal wave?

Answer 12

-Are vibrations along the direction of travel
-Sound waves (340m/s)
-Consists of alternate compressions and rarefactions of the medium it’s travelling through
-These cause pressure variations in the medium

Question 13

What is compression?

Answer 13

-When the molecules are closer together, increasing the pressure at that point

Question 14

What is rarefaction?

Answer 14

-When the molecules are further apart, decreasing the pressure at the point

Question 15

What is reflection?

Answer 15

-The wave is bounced back when it hits a boundary, and can be demonstrated in a ripple tank

Question 16

What is refraction?

Answer 16

-The wave changes directions it enters a different medium
-This is du to the wave speeding up or slowing down

Question 17

What is intensity?

Answer 17

-Is the rate if flow of energy per unit area at right angles to the direction of the travel of the wave
-Proportional to energy, and energy is proportional to amplitude squared
-A vibration source takes four times as much energy to double the size of the vibrations

Question 18

What do all EM waves have in common?

Answer 18

-Travel in a vacuum at a speed of 3x10^8m/s and at slower speeds in other media
-Transverse consisting of vibrating electric and magnetic fields
-Can be refracted, reflected and diffracted and can undergo interference
-Can be polarised