P4 | waves

Question 1

what is sound with frequencies greater than 20,000Hz known as?

Answer 1

ultrasound

ultra = beyond

Question 2

what is sound with frequencies less than 20Hz known as?

Answer 2

infrasound

infra = below

Question 3

why does sound travel faster in liquids than in gases?

Answer 3

sound travels faster in liquids because the molecules are more tightly packed

Question 4

wave speed formula

Answer 4

v = λ x f

Question 5

what happens to frequency as sound waves travel from a less dense to more dense medium?

Answer 5

stays constant

Question 6

what happens to wave speed as sound waves travel from a less dense to more dense medium?

Answer 6

increases

Question 7

what happens to wavelength as sound waves travel from a less dense to more dense medium?

Answer 7

increases

Question 8

why is it difficult to predict when an earthquake will happen?

Answer 8

movement of tectonic plates/release of energy in earth’s surface is sudden/random and it is difficult to measure when the release of energy will occur/plates will collide

Question 9

order of earth’s structure (outer most to inner most)

Answer 9

crust (solid)
mantle (semi-solid)
outer core (liquid)
inner core (solid)

Question 10

properties of p waves

Answer 10

primary waves (arrive first)

can travel through solids and liquids therefore they can pass through all of earth’s layers

longitudinal

shake the ground up and down

Question 11

properties of s waves

Answer 11

secondary waves (arrive second)

can only travel through solids

transverse

shake the ground side to side

Question 12

what should you always do to your answer for sonar pulse calculations?

Answer 12

divide by 2 at the end

Question 13

how do scientists use seismic stations to locate where an earthquake happened?

Answer 13

work out the time between S and P waves to find out the time delay between them

d = s x t to calculate the distance the wave travelled

pick three stations and draw circles with the possible maximum distance

where they overlap is the epicentre (called triangulation)

Question 14

what is S-P time

Answer 14

time difference between arrival of P waves and S waves

Question 15

how is UV light used to check bank notes?

Answer 15

UV light absorbed by banknote which emits light into eye

Question 16

uses of infrasound

Answer 16

• investigating the internal structure of earth

- communication between elephants/dolphins

Question 17

uses of ultrasound

Answer 17

• foetal scanning

- animal communication

Question 18

how does sound travel through air?

Answer 18

sound waves travel along vibrations of air particles parallel to the direction of energy transfer as longitudinal waves

Question 19

how are sound waves detected by an ear?

Answer 19

• sound waves are collected by the outer ear (pinna)
• the waves travel along the ear canal
• the waves reach the eardrum and make it vibrate
• small bones called ossicles amplify the vibrations
• the cochlea turns these into electrical signals
• the auditory nerve takes the signals to the brain

Question 20

how are ultrasounds used for foetal scanning?

Answer 20

• ultrasound waves pass through the body
• when they reach the boundary between fluid in the womb and the skin of the foetus, some of the wave is reflected back and detected
• the exact timing and distribution of the waves are processed by a computer to produce a video image of the foetus