Using Waves

Question 1

how do changes in velocity, frequency and wavelength relate in transmission of sound waves changing between mediums?

Answer 1

• Velocity of sound is directly proportional to the wavelength so if the velocity of sound doubles when it travels from one medium to another, its wavelength also doubles.
• The frequency of sound depends upon the source of sound, not the medium of propagation. Hence, it does not change.
• This change in velocity can also result in a change of direction of the sound wave- refraction

Question 2

what do reflection ray diagrams look like?

Answer 2

• horizontal line with diagonal dashes underneath it representing a mirror
• dotted normal line in the centre above the mirror
• angle between incident ray and normal is angle of incidence
• angle between reflected ray and normal line is angle of reflection

Question 3

describe a process that converts sound wave disturbances between vibrations in solids

Answer 3

• Sound waves enter the ear canal and cause the eardrum to vibrate.
• Three small bones transmit these vibrations to the cochlea.
• This produces electrical signals which pass through the auditory nerve to the brain, where they are interpreted as sound.

Question 4

why does the process of the ear detecting sound only work over a limited frequency range?

Answer 4

The cochlea designed so that it is only stimulated by a limited range of frequencies. This means that humans can only hear certain frequencies.

Question 5

what is the human range of hearing?

Answer 5

20Hz to 20,000HZ (20KHz)

Question 6

how are ultrasound waves used to form images of internal structures in both medical and industrial imaging?

Answer 6

• their ability to do this relies on what happens when they meet the boundary between two different materials:
• some of the ultrasound waves are reflected at the boundary using a source
• the time taken for the waves to leave a source and return to a detector is measured
• the depth of the boundary can be determined using the speed of sound in the material and the time taken detected by a detector

Question 7

what are the two types of seismic waves?

Answer 7

• P-waves, which are
  longitudinal waves
• S-waves, which are
  transverse waves

Question 8

what can P-waves travel through and what does this tell us about the structure of the earth?

Answer 8

• solids and liquids
• P-waves are detected on the opposite side of the Earth. Refractions between layers cause two shadow zones where no P-waves are detected. The size and positions of these shadow zones indicate there is a solid inner core.

Question 9

what can S-waves travel through and what does this tell us about the structure of the earth?

Answer 9

• solids only
• S-waves are not detected on the opposite side of the Earth - this suggests that the mantle has solid properties, but the outer core must be liquid.

Question 10

how does echo sounding use high frequency sound waves to detect objects in deep water and measure water depth?

Answer 10

• The time between a pulse of sound being transmitted and detected and the speed of sound in water can be used to calculate the distance of the reflecting surface or object.
• The process is very similar to ultrasound imaging. However, the sound waves used are within normal hearing range, and they are used to identify objects rather than internal structures.

Question 11

what does a lens do and how?

Answer 11

it forms an image by refracting light

Question 12

what is focal length?

Answer 12

the distance from the lens to the principal focus

Question 13

what represents a convex lens?

Answer 13

|
v

Question 14

what represents a concave lens?

Answer 14

v
|

Question 15

what does a convex lens do to rays?

Answer 15

it brings (converges) rays together

Question 16

what does a concave lens do?

Answer 16

it spreads (diverges) rays out

Question 17

what does F represent on a lens ray diagram?

Answer 17

focal length

Question 18

what 3 things are the images concave lenses always produce no matter the position of the object?

Answer 18

• upright
• diminished
• virtual

Question 19

how to draw a lens ray diagram

Answer 19

• Draw a horizontal ray from the top of the object to the lens that is parallel to the principal axis.
• Once through the lens, the ray should pass through the principal focus on either the right or on the left via following the line back through the lens with a dotted line
• Draw a ray which passes from the top of the object through the centre of the lens.
• draw a line from the crossover of the two rays to the centre of the diagram with an arrow pointing towards the crossover to represent the image

Question 20

what 6 things can the images from convex lenses be?

Answer 20

• upright or inverted (upside down compared to the object)
• magnified or diminished (smaller than the object)
• real or virtual

Question 21

what 3 image characteristics does a convex lens produce if the object is placed more than 2F (camera)?

Answer 21

• real
• inverted
• diminished

Question 22

what 3 image characteristics does a convex lens produce if the object is placed between F and 2F (telescope)?

Answer 22

• real
• inverted
• magnified

Question 23

what 3 image characteristics does a convex lens produce if the object is placed less than F (magnifying glass)?

Answer 23

• virtual
• upright
• magnified

Question 24

what happens in a convex lens diagram if the two rays do not cross on the right of the lens?

Answer 24

• even though both are pointing downwards they will not meet on the right
• follow both lines left past the lens with dotted lines until they cross
• this is a magnifying glass

Question 25

how is the colour of an object related to the differential absorption and reflection of different wavelengths of light by the object?

Answer 25

• It’s determined by which wavelengths of light are more strongly reflected (it can be detected by our eyes)
• Wavelengths that are not reflected are absorbed which are not detected by our eyes
• If all wavelengths are reflected equally the object appears white. If all wavelengths are absorbed the objects appears black.

Question 26

how is the colour of an object related to the differential transmission of different wavelengths of light by the object?

Answer 26

• if a light wave is passed across or through a transparent material before hitting an object:
• they are very good at transmitting light with very little absorption so the colour should not change
• if a light wave is passed across or through a translucent material before hitting an object:
• the translucent material transmits some light and is not completely clear

Question 27

describe the effect of on light of passing through coloured filters

Answer 27

• All colours are absorbed except for the colour of the filter.
• For example, an orange filter transmits orange light but absorbs all the other colours.
• If white light is shone on an orange filter, only the orange wavelengths will be observed by the human eye.

Question 28

what happens to coloured objects in coloured light?

Answer 28

• it will appear black/ very dark if the colour of light does not contain the wavelength of the same colour as the wavelength the object reflects since there is none of that colour to reflect
• it will appear the same colour as in white light if the light contains the wavelength of colour that is the same wavelength that the object reflects
• An object appears to be black if it absorbs all the wavelengths of visible light.
• For example, an object that appears blue in white light will appear black in red light.
• This is because the red light contains no blue light for the object to reflect.

Question 29

why do opaque objects have a particular colour?

Answer 29

because our eyes cant see the wavelenghts (colours) it absorbs but can see he wavelength (colour) of light that it reflects

Question 30

what colour of light is made if red and blue light is mixed together?

Answer 30

magenta

Question 31

what colour of light is made if red and green light is mixed together?

Answer 31

yellow

Question 32

what colour of light is made if green and blue light is mixed together?

Answer 32

cyan

Question 33

what colour of light is made if red, green and blue light is mixed together?

Question 34

what emits and absorbs infrared radiation?

Answer 34

all bodies (objects) no matter the temperature

Question 35

what happens (in terms of infrared radiation) the hotter the body?

Answer 35

• the more infrared radiation it gives out in a given time
• the greater the proportion of emitted radiation is visible light

Question 36

what is a perfect black body?

Answer 36

an object that absorbs all the radiation incident on it

Question 37

why is a perfect black body the best possible emitter?

Answer 37

• it would absorb all the radiation that falls on it
• it would not reflect or transmit any radiation
• an object that is good at absorbing radiation is also a good
  emitter (material that sends out energy)

Question 38

why when temperature is increased does the intensity of shorter wavelength radiation increase more rapidly than longer wavelengths?

Answer 38

because shorter wavelength EM radiation transfers more energy

Question 39

what is the temperature of a body related to?

Answer 39

the balance between the amount of incoming radiation absorbed and radiation emitted

Question 40

what does the temperature of the earth depend on and why?

Answer 40

• the rates at which radiation (light and infrared) is absorbed and emitted by the Earth’s surface and atmosphere
• because the planet’s internal energy increases and the surface gets hotter.

Question 41

what happens to the temperature of a body if the rate of absorption is greater than the rate of emission?

Answer 41

it increases

Question 42

what happens to the temperature of a body if the rate of absorption is the same as the rate of emission?

Answer 42

it is constant

Question 43

what happens to the temperature of a body if the rate of absorption is less than the rate of emission?

Answer 43

it decreases