Waves 2 Flashcards
What is a transverse wave?
A wave where vibrations occur perpendicular to the direction the wave is travelling
What is a longitudinal wave?
A wave where vibrations occur parallel to the direction the wave is travelling
Define amplitude
The maximum distance between the peak or trough of a wave and its equilibrium point
Define wavefront
A horizontal line drawn linking all the peaks in a set of waves
Define wavelength
The distance from point on a wave to the same point on the next wave
Define frequency
Number of waves per second
Define the period of a wave
Time taken to complete one wave cycle
Equation for wave speed
Wave speed = frequency x wavelength
Equation for wave frequency
Frequency = 1 / time period
What property do all waves have in common?
They can be reflected and refracted
What is the Doppler effect?
The change in frequency and wavelength caused by relative movement of the source of wave or observer
Give an example of the Doppler effect in sound waves
- When an ambulance goes past you the siren decreases in pitch
- This is because the wavelength of the sound waves increases
Give an example of the Doppler effect in light waves
- Light from distant planets looks red (it’s red-shifted)
- Because planets are moving away from us so wavelength becomes longer and therefore moves to the red spectrum
Which EM waves can be used in cooking?
Microwaves and infrared radiation
Which EM wave causes burns?
- Infra-red radiation
Which EM wave causes skin cancer
UV
What are the dangers of X-rays and gamma rays?
- Ionising radiation
- Mutation
- Cancer
What do all EM waves have in common?
- All transfer energy
- All travel at the same speed in a vacuum
- Can be reflected, refracted and diffracted
- All transverse waves
What are the advantages of optic fibres?
- Carry more information per second
- More secure
How are x-rays and gamma rays similar?
- Both short wavelength EM waves
- Carry lots of energy per second
How do x-rays and gamma rays differ?
- X-rays are made when electrons moving at high speeds are stopped
- Gamma rays are released from unstable nuclei
- Gamma is more penetrative
- Gamma has shorter wave length
Describe the properties of light waves
- Transverse wave
- Transfer energy
- Can be reflected, refracted, diffracted
- A wave where vibrations occur perpendicular to the direction the wave is travelling
What is a normal line?
A line drawn perpendicular to the mirror
What is the law of reflection?
- Angle of incidence = angle of reflection
What is refraction?
A change in direction of waves when they travel across a boundary from one medium to another
Describe how a light ray changes direction when it enters and leaves a glass block
- Bends towards the normal as it enters the block
- Bends away from the normal as it leaves the block
Snell’s law (refractive index)
n = sin i / sin r
Define critical angle
Angle of incidence beyond which rays of light are totally internally reflected
Define total internal reflection
- When the angle of incidence is greater than the critical angle
- All light is reflected, none is refracted
How do optical fibres work?
- Total internal reflection
- Core of fibre made out of glass with high refractive index
- Cladding is made out of glass with lower refractive index
- Light entering core is at an angle greater than the critical angle so light is TIR
Give examples of the use of optical fibres
- Endoscope - used in keyhole surgery
- Communication as less energy is lost when compared to using copper wiring
Critical angle
sin c = 1 / refractive index (n)
Describe the properties of sound waves
- Longitudinal waves
- Transfer energy
- Can be reflected, refracted and diffracted
