## When a sound source is moving towards the observer?

When the sound source moves toward an observer, each successive wave is emitted closer to the observer than the previous wave and takes just a little less time to reach the observer than the previous one. Since the time between waves is reduced, the frequency is increased.

## When observer is at rest source is moving away from observer?

We can say that if the observer is moving towards the source, its velocity is positive, or greater than zero, while if it is moving away from the source, its velocity is negative, or less than zero.

## When a light source is moving towards the observer?

1. If the light source is moving away from the observer (positive velocity) then the observed frequency is lower and the observed wavelength is greater (redshifted). 2. If the source is moving towards the observer (negative velocity), the observed frequency is higher and the wavelength is shorter (blueshifted).

## What happens to a light source as it is moving towards you?

When the source of waves moves toward you, the wavelength decreases a bit. If the waves involved are visible light, then the colors of the light change slightly.

## When a source is moving away from the observer what occurs with the wavelength?

If the observer is stationary but the source moves toward the observer at a speed vs, the observer still intercepts more waves per second and the frequency goes up. This time it is the wavelength of the wave received by the observer that is effectively shifted by the motion, rather than the speed.

## What happens to the perceived frequency as the source is moving towards the observer?

Motion toward the source increases frequency as the observer on the right passes through more wave crests than she would if stationary. Motion away from the source decreases frequency as the observer on the left passes through fewer wave crests than he would if stationary. Relative motion apart decreases frequency.

## Is there a Doppler shift if the source and observer move in the same direction?

Note that if the observer and source are moving at the same speed in the same direction, no frequency change is detected. This type of change in frequency due to motion is called the Doppler effect.

## What week is the color Doppler done?

The first fetal growth scan is suggested to be done between 28 weeks and 32 weeks of pregnancy to determine the growth and fetal wellbeing. The second growth scan and colour Doppler studies are done closer to the due date, which is between 36 and 40 weeks.