Chapter 13 Waves Flashcards
What is a wave?
A wave is made up of particles in periodic motion. It is a disturbance that transfers energy from one place to another, but does not transfer matter during the energy transfer.
Define periodic motion
Motion repeated at regular intervals
Define oscillation/ vibration
One complete cycle of periodic motion
Define how the particles of longitudinal waves travel.
Particles of a longitudinal wave vibrate parallel to the direction of travel of the wave motion.
Define how the particles of a transverse wave travel.
Particles of a transverse wave vibrate perpendicular to the direction of travel of the wave motion.
Define compression.
Compression is the part where particles are closest to one another and where air pressure is slightly higher than the surrounding air pressure.
Define rarefaction.
Rarefaction is the part where particles are spread apart and where air pressure is slightly lower than the surrounding air pressure.
Define crests and troughs.
Crests are the highest points and troughs are the lowest points of a transverse wave.
Define amplitude of a wave and state its SI unit.
The amplitude A of a wave is the maximum displacement of a point from the equilibrium position/ its rest position. The SI unit is metre (m).
Define the wavelength of a wave and state its SI unit.
The wavelength of a wave is the shortest distance between any two points that are in phase/ distance between 2 successive crests or troughs. The SI unit is metre (m).
Define period of a wave and state its SI unit.
The period T of a wave is the time taken to produce one complete wave/ time taken for any point of the wave to move a distance of one wavelength. The SI unit is second (s).
Define frequency of a wave and state its SI unit.
The frequency f of a wave is the number of complete waves produced per second/ the number of crests/ troughs that pass a point per second. The SI unit is hertz (Hz).
Explain what it means for the points of a wave to be ‘in phase.’
Points along a wave are in phase if they have the same direction of motion, same speed and same displacement from their rest position.
Define wave speed and state its SI unit.
Wave speed v is the distance travelled by a wave per second. The SI unit is metre per second (m s^-1)
How are frequency and period related?
They are related by the equation f = 1/T
Define the normal.
The normal is an imaginary line that is perpendicular to the plane surface.
What is the difference between displacement-distance graphs and displacement-time graphs?
A displacement-distance graph describes the displacements of all particles at a particular point in time, while a displacement-time graph describes the displacement of one particle over a time interval.
Define wavefront
A wavefront is an imaginary line on a wave that joins all adjacent crests of a wave or all adjacent points that are in phase.
What are the quantities that can be obtained from displacement-distance graphs and displacement-time graphs respectively?
Displacement-distance: obtain amplitude and wavelength
Displacement-time: obtain amplitude and period
Define angle of incidence and angle of reflection. (in the context of waves)
The angle of incidence is measured from the normal to the direction of travel of the incident wave. Similarly, the angle of reflection is the angle between the normal and the direction of travel of the reflected wave. Thus the angle of incidence is equal to the angle of reflection.
How is the speed and wavelength of waves affected after being reflected off a surface?
There is no change in the speed and wavelength after reflection.
Describe the changes that take place when waves enter a shallow region at an angle and refract.
As depth reduces, wavelength becomes smaller (space between the adjacent wave fronts are smaller).
Depth decrease → speed decrease → wave bends toward the normal (angle is smaller because speed decreases)
Frequency remains the SAME.
Describe the changes that take place when waves enter a deeper region at an angle and refract.
As depth increases, wavelength becomes larger (space between the adjacent wave fronts are larger).
Depth increase → speed increase → wave bends away from the normal (angle is larger because speed increases)
Frequency remains the SAME.
