7. Waves

Question 1

what is meant by wave motion as illustrated by vibration in ropes, springs and ripple tanks

Question 2

displacement, amplitude, phase difference, period, frequency, wavelength and speed

Answer 2

frequency- the number of wavefronts/crests/troughs passing a fixed point per unit time. OR. the number of oscillations per unit time (of source/point on wave/particle of medium).

wavelength- distance moved by wavefront/energy during one oscillation/cycle/period of source. minimum distance between two wavefronts. distance between two adjacent wavefronts.

period- time for one oscillation/cycle/vibration. time between adjacent wavefronts passing the same point. shortest tome between two wavefronts passing the same point.

Question 3

cathode-ray oscilloscope (CRO)

Answer 3

use of the time-base and y-gain of a cathode-ray oscilloscope (CRO) to determine frequency and amplitude

Question 4

derive wave speed equation

Answer 4

v = f λ

Question 5

progressive wave

Answer 5

energy is transferred

Question 6

intensity

Answer 6

intensity = power/area and intensity ∝ (amplitude)^2 for a progressive wave

Question 7

compare transverse and longitudinal waves

Answer 7

transverse- have vibrations/oscillation of the particles/wave perpendicular to the direction of the propagation of the energy/transfer of energy.

longitudinal- have vibrations/oscillation of the particles/wave parallel to the direction of the propagation of the energy/transfer of energy.

Question 8

analyse and interpret graphical representations of transverse and longitudinal waves

Question 9

Doppler’s effect

Answer 9

when a source of sound waves moves relative to a stationary observer, the observed frequency is different from the source frequency. (increases when source comes closer).

observed frequency= (source frequencywave speed) / (wave speedsource speed)

fο = fsv /(v ± vs)

Subtract when coming closer do smaller denominator and greater observed frequency

Question 10

electromagnetic waves

Answer 10

all electromagnetic waves are transverse waves that travel with the same speed c in free space- 3*10^8 m^s-1.

Question 11

range of EMW wavelengths in free space

range visible to human eye

Answer 11

radio
microwaves
infrared radiation
visible light
ultraviolet
x-rays
gamma rays

range 400–700nm in free space are visible to the human eye. vibgyor- increasing wavelength.

Question 12

polarisation

Answer 12

phenomenon associated with transverse waves.

oscillations are in a single direction, which is perpendicular to the direction of propagation (of the wave). or
oscillations are in a single plane, which contains the direction of propagation of the wave.

Question 13

Malus’s law

Answer 13

(I = I0 cos2θ )

to calculate the intensity of a plane-polarised electromagnetic
wave after transmission through a polarising filter or a series of polarising filters