1. Doppler Effect Change in frequency when a source of sound is moving relative to an observer. Source of sound moving Source of sound stationary Hears lower frequency Hears higher frequency Link Link train

2. Derive the expression for the apparent frequency detected when a source of sound waves relative to stationary observer. Speed of source v s, source frequency f s, speed of sound v, Source moving toward stationary observer Source moving away from stationary observer For observer f = f s v v - v s () For observer f = f s v v + v s ()

3. The distance the source travels in 1 period = v s t =v s T = v s ÷ f s (observer) = distance travelled first wave in I period – distance travelled by source and 2 nd wave in 1 period. = v - v s f s f s = 1 ( v – v s ) f s For observer f = v ÷ = f s v v - v s () Source travelling towards observer

4. Derive the expression for the apparent frequency detected when an observer moves relative to a stationary source Speed of observer v o, frequency f s, speed of sound v, observer moving toward stationary source observer moving away from source For observer f = f s v + v o v () For observer f = f s v - v o v ()

5. Observer travelling towards source at speed v o The number of waves produced in time t = ft = vt Extra waves heard in time t = v o t Total no of waves heard = v o t vt + vt No of waves per second = frequency = v o t + (  ÷ t f = f s v + v o v () As = v ÷ f s Now do tutorial questions