A Doppler flow meter sends ultrasonic waves into a blood vessel. Blood flowing towards the meter reflects waves of what frequency?

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_