1. SSS TWO PHYSICS FIRST TERM
WAVE MOTION
2ND LECTURE

2. Characteristics of waves
Reflection
Refraction
Diffraction
Interference (constructive and destruction)
Rectilinear propagation

3. Terms used in wave
Amplitude (A) This is the maximum displacement of a particle from its rest or equilibrium position. It is measured in metre(m) Period (T) This is the time required for a particle to make one complete cycle or oscillation. It is measured in second(sec or s) Frequency(f) This is the number of cycle or oscillations which the wave makes in one second. It is measured in Hertz (Hz).

4. Wavelength(λ)
This is the distance between two successive crests or troughs. It is measured in metre(m).
Wave speed(v)
This is the distance which the wave travels per unit time. It is measured in metre per second (m/s).
SOME FORMULAE USED IN WAVE
V = fλ
F = 1/T
Y = Asin(kx – wt)
Where A = Amplitude, K = 2π/λ w = 2πf

5. Calculations on wave motion
Example 1
A radio station broadcasts at a frequency of 200kHz. If the speed of the wave is 300,000,000m/s. Calculate (i) period (ii) the wavelength of the wave.
Solution
Period T = 1/f = 1/200,000 = sec.
Wavelength λ = v/f = / = 1500m

6. Y = 5sin(3x – 4t)------------------(i)
Example 2
The equation y = 5sin(3x – 4t), where y is in millimetres, x is in metres and t is in seconds represents a wave motion. Determine the
Frequency (ii) period and (iii) speed of the wave.
Solution:
Y = 5sin(3x – 4t) (i)
Let y = Asin(kx – wt) (ii)
A = Amplitude = 5m
Comparing equations (i) and (ii)
W = 4, 2πf = 4
f = 4/2π = 4/2 x = 4/6.284= 0.64Hz
T = 1/f = 1/0.64 = 1.56sec
k = 3,
2π/λ = 3, λ = 2π/3
Hence, v = f λ = 0.64 x (2π/3) = 1.34m/s

7. Assignment
The equation y = asin(wt–kx) represents a plane wave travelling in a medium along the x-direction, y being the displacement at the point x at time t.
(i) Given that x is in metres and t is in seconds,
state the units of k and w.
(ii)What physical quantity does it represent?
Justify your answer.
(iii)State whether the wave is travelling in the
positive or negative x-direction.