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Flashcards in Waves Deck (33)
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Describe what is meant by wave motion as
illustrated by vibration in ropes and springs

- Waves on ropes can be produced by moving one end of the rope from side to side repeatedly. This action sends waves along => each part of the rope vibrates from side to side
- Waves on a spring can be produced by fixing one end of the spring and moving the other end repeatedly to and fro. Each part of the spring vibrates and makes the next part vibrate


Describe what is meant by wave motion as
illustrated by experiments using water waves

Make straight waves by moving ruler up and down on the water surface. The wavefronts travel away from ruler. This is wave motion. Straight wavefronts are plane waves


Wave equation

velocity = frequency x wavelength
period = 1/ freq.
frequency= 1/period


Definition of frequency

the number of complete waves passing a point. Measured in Hertz


Definition of wavelength

is the distance of one wave crest to the next


Definition of amplitude

is the height of the wave crest/the depth of the wave trough from the middle.


Distinguish between transverse and longitudinal
waves and give suitable examples

- The vibrations of the waves are perpendicular to the direction the waves are travelling in
- Can be polarised or unpolarised
e.g. light
- The vibrations of the waves are parallel to the direction of the waves are travelling in
- Cannot be polarised
e.g. sound


Describe the use of water waves to show:
– reflection at a plane surface
– refraction due to a change of speed
– diffraction produced by wide and narrow gaps

Reflection (fig.7.3.1 pg108 to support)
- Plane waves reflect from a straight barrier at the same angle to the barrier as the same incident waves
- Incident waves in deep water is refracted when entering shallow water due to change of speed
- The narrower the gap, the more the waves spread out


Relationships between angle of incidence and reflection



Describe the formation of an optical image by a
plane mirror, and give its characteristics

The image in the mirror is the same size as the object
The image is behind the mirror


From shallow to deep water/ From glass to air

away from normal


Definition of refractive index in terms of speed and its equation

Def: is a measure of the change of direction of a light ray at non-normal incidence when it passes from air into substance, therefore changes speed at boundary
Eq: speed of light in air/speed of light in substance = sin i/ sin r


Use the terminology for the angle of incidence i and
angle of refraction r and describe the passage of
light through parallel-sided transparent material

Angle of incidence > Angle of Refraction when light travels from a less dense material to a more dense material.
Likewise, the opposite occurs when light travels from a dense medium to a less dense medium.


Definition of critical angle

The angle of incidence at which maximum refraction occurs is called the critical angle


As the angle of incidence increases

- There is less refraction
- There is more reflection


Angle of incidence < critical angle
Angle of incidence = critical angle
Angle of incidence > critical angle

- Refraction away from normal
- Angle of refraction is 90 degrees/ Refracts along the surface
- Total Internal Refelection


Describe internal and total internal reflection

Total: because all energy is reflected
Internal: all energy stays within the material
Reflection: light is reflected


Describe the action of optical fibres particularly in medicine and communications technology

Optical fibers are essentially cables made from high-quality glass.
When light enters one end of an optical fiber cable, it undergoes total internal reflection until it reaches the end of the cable.
The advantages of using optical fiber is
- signals carried by the optical fiber do not weaken over long distances
- optical fiber cables can carry a larger quantity of information
- can be transmitted at high speeds since digital information can be converted to visible light or infrared signal and be sent across optical fiber cables.


Describe the action of a thin converging lens on a
beam of light (use the term principal focus and focal length)

Parallel rays of light when entering a converging lens will be focused at one point. This point is the principal focus. The focal length is the distance from the lens to the principal focus


Applications of the converging lens

- beyond 2F: real, inverted, diminished (for camera)
- at 2F: real, inverted, same size
- between F and 2F: real, inverted, magnified (for projector)
- at F: no image/ image appears at infinity
- between F and the lens: virtual, upright, magnified (for magnifying glass)


Definition of monochromatic light

one-coloured light


Definition of dispersion and give examples

the splitting of monochromatic light into separate colours.
An example would be the splitting of white light using glass prism, the effect occurs because the refractive index of glass varies with the colour of the light


State the approximate value of the speed
of electromagnetic waves

300 000 km/s through space
All electromagnetic (e.m) waves travel through space at the same speed


List the e.m spectrum in order of decreasing wavelengths

radio waves -> microwaves -> infra-red -> light -> ultraviolet -> x-rays -> gamma rays


Role of each e.m spectrum

- Radio waves for radio, TV, mobile phone communications
- Microwaves for satellite, telephone, heating food
- Infra-red for electrical appliances, remote controllers, optical fibre
- Light for photography and optical instruments
- Ultraviolet for security markers, sunbeds
- X-rays for airport security and kill cells
- Gamma rays for radiotherapy and killing cancer cells


Demonstrate an awareness of safety issues
regarding the use of microwaves and X-rays

- Microwaves can penetrate into the body and have a heating effect on body tissues. Brain damage and cancer
- X-rays can cause cell damage and cancers


State the approximate range of audible frequencies

20Hz to 20kHz


State the order of magnitude of the speed
of sound in air, liquids and solids

air (340 m/s) -> liquid (1400 m/s) -> solid (3000 m/s)


How is sound produced?

By vibrations


Describe the longitudinal nature of sound waves

When waves pass through air, the air molecules move forwards and backwards along the direction in which the waves are moving. Therefore, sound waves are longitudinal because the vibrations are along/parallel to the direction they travel in