P5.1 - Wave Behaviour

Question 1

What are longitudinal waves with an example?

Answer 1

• Longitudinal waves vibrate parallel to the direction
  of energy transfer of the waves.
• Sound waves are longitudinal waves.

Question 2

What are transverse waves with an example?

Answer 2

• Transverse waves vibrate perpendicular to the
  direction of energy transfer of the waves.
• Light waves are transverse waves.

Question 3

What is a wave?

Answer 3

A wave is a disturbance in a medium that transfers energy without transferring matter.

Question 4

What should wave diagrams be imagined to be doing?

Answer 4

• Waves are always in motion.
• Wave diagrams are drawn stationary, but the
  waves should be imagined to be moving left to
  right, in the direction of energy transfer.

Question 5

What is the normal line?

Answer 5

The mean position of a particle, about which it vibrates/oscillates.

Question 6

What is the amplitude?

Answer 6

• The maximum displacement of particles from
  their mean position.
• The bigger the amplitude, the more energy the
  wave carries.

Question 7

What is the wavelength?

Answer 7

• The distance from one point on a wave to the
  same point on the next wave.
• Distance from one peak (or trough) to the next
  peak (or trough).

Question 8

What is the frequency?

Answer 8

• The number of waves or oscillations, passing a
  point every second (number of peaks passing a
  point every second - easier way)..
• The bigger the wavelength the smaller the
  frequency.

Question 9

What is the time period?

Answer 9

The time for a wave to complete one oscillation is the time period for a wave.

Question 10

What is the difference between a time trace and a snapshot?

Answer 10

• A time trace shows how displacement varies with
  time at a particular position.
• In a time trace you could measure the period from
  any point on a wave to the same point on the next
  wave.
• A snapshot of a wave shows how displacement
  varies with distance as a particular time.
• On a snapshot you can measure wavelength from
  any point on the wave to the same point on the
  next wave.
• On either diagram you can measure amplitude
  from the middle to the top or the bottom of a wave.

Question 11

How are transverse waves represented using wave diagrams?

Answer 11

• Transverse waves are easily represented using
  wave diagrams.
• The peaks and troughs are perpendicular to the
  normal line.

Question 12

How are longitudinal waves represented on a wave diagram?

Answer 12

• Compressions - Particles squashed together, high
  pressure - PEAKS
• Rarefactions - Particles spread far apart, low
  pressure - TROUGHS

Question 13

What is the wave equation?

Answer 13

c = f x (Lambda)

c = wave speed                m/s
f = frequency                    Hz
Lambda = Wavelength    m

Question 14

What is the equation for time period?

Answer 14

T=1/f

Question 15

How are sound/mechanical waves created?

Answer 15

• Create by vibrating particles.
• Which collide with neighbouring particles.
• Transferring kinetic energy.

Question 16

How can you prove that a wave travels, not the water?

Answer 16

• Using ripples on motor waves.
• Put a small cork on the surface.
• You can see the waves moving up and down on the
  surface as the wave moves through the water but the
  cork still in the same position.
• The wave travels but the water does not.

Question 17

How do you measure the velocity of ripples?

Answer 17

You need to know the frequency of the ripples and their wavelength to calculate the velocity.

• Find the wavelength by using a strobe and a ruler.
• Find the frequency of the number of rotations of the
  motor per second.
• Use the wave equation to calculate the wave velocity.

Question 18

Describe in four steps how the sound of a cymbal is heard?

Answer 18

1. The cymbal vibrates.
2. The air particles around the cymbal start to vibrate.
3. Particles collide with neighbouring particles, causing
   them to start to vibrate, transferring energy from left
   to right.
4. The ear detects vibrating air particles.

Question 19

What is ultrasound?

Answer 19

Ultrasound is the name given to sound waves with a frequency greater than 20,000Hz.

Question 20

Give some uses of ultrasound scans.

Answer 20

• Image a baby inside a womb.

- Detecting cracks in metal pipes and buildings.

Question 21

Describe how an ultrasound forms an image.

Answer 21

• The transducer is a device that produces
  ultrasound waves by causing a crystal to vibrate
  very rapidly.
• The transducer beams ultrasound waves.
• The ultrasound waves are partially reflected every
  time they cross a boundary between different
  media.
• The reflected ultrasound waves return to the
  transducer as a series of pulses, which are
  deciphered to form an image.
• The machine calculates the distances to form the
  image using the time and velocity.

Question 22

How does you ear detect sound?

Answer 22

• The outer ear (pinna and auditory canal) gathers
  the sound wave and directs it to the ear drum
  which vibrates.
• As the ear drum vibrates, it makes the ossicles
  (the hammer, anvil and stirrup) vibrate.
• The ossicles act like small levers to amplify the
  vibration and pass it on to the inner ear through
  the oval window.
• The cochlea is shaped like a snail shell and
  contains fluid which transmits the movement of
  the oval window to small hairs on the inside wall
  of the cochlea.
• These hairs are attached to sound-detecting
  cells that release chemical substances, which
  makes nerves send a signal down the auditory
  nerve to your brain.
• Your brain processes the signal and you hear the
  sound.

Question 23

What is the natural frequency of an object?

Answer 23

The natural frequency of an object is the frequency at which an object oscillates if it is displaced.

Question 24

What does the range of frequencies of sound you can hear depend on?

Answer 24

• The hairs in you cochlea can vibrate.
• The hairs inside the cochlea in your ear have
  different lengths and resonate at different
  frequencies in the sound wave.
• The range of frequencies that you can hear
  depends on the range of length of hears in your
  cochlea.
• Shorter hairs resonate at high frequencies.
• Longer hairs resonate at low frequencies.

Resonance - The large amplitude oscillation that happens when you make something oscillate at its natural frequency.

Question 25

What happens to your sense of hearing as you get older and why?

Answer 25

As you get older you lose the shorter hairs in your cochlea. This means that you find it more difficult to hear higher frequencies.