NSC / Matric Doppler Effect — practice questions

1. The effect appears whenever the source of a wave and the observer move relative to each other. 2. What the observer measures is a different frequency from the one the source is emitting. 3. So the Doppler effect is a change in the observed frequency of the wave. 4. The speed of sound in the medium is not altered by the motion of the source. _Source: Siyavula Physical Sciences Grade 12 (Everything Science, CC BY 4.0), Chapter 6: Doppler effect_

1. Frequency measured by an observer is the number of complete wave cycles that pass in each second. 2. A cyclist riding towards the siren runs into crests that would otherwise have taken longer to arrive. 3. More complete cycles therefore pass the cyclist each second than pass a still listener. 4. So the measured frequency is higher than the frequency the siren emits. 5. It cannot stay equal, since equality happens only when there is no relative motion between source and observer. _Source: Siyavula Physical Sciences Grade 12 (Everything Science, CC BY 4.0), Chapter 6: Doppler effect_

1. The meter transmits ultrasonic waves that are reflected by the moving blood cells. 2. Reflection from a moving object shifts the frequency, exactly as the Doppler effect predicts. 3. Blood moving towards the meter shifts the reflected sound to a higher frequency. 4. Blood moving away shifts it to a lower frequency, which is how the direction of flow is read. 5. An unchanged frequency would mean the blood was not moving relative to the meter at all. _Source: Siyavula Physical Sciences Grade 12 (Everything Science, CC BY 4.0), Chapter 6: Doppler effect_