P4 - The nature and properties of waves Flashcards
Describe what waves do [1]
They transfer energy without transferring matter
What is a mechanical wave? [1]
A wave that needs a medium to travel through
What is a wavefront? [1]
A line on which the disturbance caused by waves has the same phase at all points (e.g. the crests of waves in a ripple tank)
Define frequency [2]
The number of waves per second / measured in hertz Hz
Define wavelength [1]
The same point on neighbouring waves
Define amplitude [1]
The maximum displacement caused by a wave
Describe waves that are in the same phase [2]
Waves that have the same speed and direction
Describe the motion of particles in a transverse wave and give an example [1]
Particles vibrate perpendicular to the direction of energy transfer / light
Describe the motion of particles in a longitudinal wave and give an example [1]
Particles vibrate parallel to the direction of energy transfer / sound
Recall the wave speed equation [1]
Wave speed = frequency x wavelength
Describe the law of reflection [1]
The angle of incidence = the angle of reflection
What causes refraction? [2]
A change in speed of the wave when it moves to a medium with a different density
What is diffraction? [1]
The spreading of waves at the edge of obstacles
What happens to a light ray that passes from a less dense medium to a more dense medium
It slows down / the ray bends towards the normal / angle of refraction is less than the angle of incidence
What is diverging light? [1]
Light rays spreading out
What is converging light? [1]
Light rays getting closer together
Define refractive index [1]
The ratio of the speeds of a wave in two different regions
Recall the equation for refractive index [1]
n = sin i / sin r
What is the critical angle? [1]
The angle of incidence where the refracted ray passes along the boundary between the two media
When does total internal reflection happen? [1]
When the angle of incidence is above the critical angle for a medium
What is total internal reflection used for? [1]]
Optical fibres in medicine and communication
Describe the action of a thin converging lens on a beam of light [1]
Bends light inwards
Define principle axis [1]
A line through the optical centre of a lens at right angles to the lens
Define principle focus (focal point) [1]
Point on a principle axis of a lens to which light rays parallel to the principal axis converge
Define focal length [1]
Distance between the optical centre and the principal focus of a lens
What is the difference between a real image and a virtual image? [1]
A real image can be produced on a screen / virtual image is one from which the light rays appear to come from that image
Recall the main features of the electromagnetic spectrum in order of frequency from radio waves to gamma-radiation [5]
Radio waves - Microwaves - Infrared - Visible light - Ultraviolet - X-Rays - Gamma-Rays
What is the same about all waves in the electromagnetic spectrum? [2]
They are all transverse waves and travel at the same speed in a vacuum
Describe uses of radiowaves [1]
Radio and television communication
Describe uses of microwaves [1]
Satellite television and telephones (also cooking food)
State the speed of electromagnetic waves in a vacuum
3.0x10⁸ m/s
Describe uses of infrared radiation [1]
Electrical appliances, remote controllers for televisions and intruder alarms
Describe uses of X-rays[1]
Medicine and security
What are the risks with microwaves? [1]
They can heat cells / cause mutations / could lead to cancer
What are the risks with U.V, X-rays and gamma rays? [3]
They are ionising radiation / cause mutations in cells / which can lead to cancer
What causes sound? [1]
Vibrating objects
What type of wave is sound? [1]
Longitudinal
What are the two features of longitudinal waves? [1]
Compressions and rarefactions
What is the range of human hearing? [1]
20-20,000 Hertz
What is needed to transmit sound waves? [1]
A medium
Which medium does sound travel faster in? [1]
Solids
Describe a sound with a high amplitude and low frequency [1]
Loud and low pitch
Describe a sound with a low amplitude and high frequency [1]
Quiet and high pitch
What can the reflection of sound causes? [1]
Echo
