14 - Nature of waves

Question 1

Transverse waves

Answer 1

• direction of oscillation is perpendicular to the direction of transmission of energy
• mechanically created by something causing a vibration in the medium
• e.g water waves, s-waves, stringed instruments

Question 2

Longitudinal waves

Answer 2

• energy and oscillations both travel in the same direction
• particles in medium are compressed or stretched (compression and rarefaction) as they ocsillate
• caused by a vibration pushing against a medium
• e.g sound waves, p-waves

Question 3

displacement/time graphs

Answer 3

• both types of wave shown as vertical oscillations with the and y-axis as the displacement of an individual particle and the x-axis as time
• distance between two crests or two troughs is the wavelength, height of a peak is its amplitude, time for one complete oscillation is the time period
• same shape as a sin graph

Question 4

equations

Answer 4

• frequency of a wave = 1/time period
• velocity of a wave = frequency*wavelength
• velocity of a wave in a string is square root of tension acting on a string by the strings mass per unit length
• speed of a water wave is root of g*depth of wave (shallower waves are slower

Question 5

EM waves

Answer 5

• always transverse
• require no medium as they continually generate themselves with perpendicular magnetic and electric field oscillations (dolphin fish dance)

Question 6

Phase

Answer 6

• the spatial difference between two coherent waves
• in phase = two waves are identically oscillating (peaks/troughs all line up)
• anti-phase = one wave is exactly 1/2 a wavelength out of phase with the other (peak of one line sup with trough of the other)
• phase difference can be written as fractions of a wavelength (e.g 5/2 wavelength), as a degree of 360 (e.g 90 degrees), or as an equivalent fraction of 2 pi radians where 2 pi radians = 360 degrees (e.g 90 degrees= 1/2 pi radians)
• reflected waves always in anti-phase with themselves