## **Core Concept**
Ultrasound (USG) waves travel through the human body by utilizing the principle of sonography, where high-frequency sound waves are transmitted through tissues. The speed of these waves depends on the properties of the tissues they are passing through, primarily their elasticity and density.

## **Why the Correct Answer is Right**
The correct answer states that USG waves travel in the human body at a rate of 1540 m/s. This is accurate because, on average, ultrasound waves travel through soft tissues of the human body at approximately **1540 meters per second**. This speed can slightly vary depending on the specific type of tissue (e.g., muscle, fat, blood, or bone), but 1540 m/s is a widely accepted average velocity for diagnostic ultrasound purposes.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option suggests a much slower speed than the actual. Given that even the slowest tissues' ultrasound velocities are significantly higher than this option, it is clearly incorrect.
- **Option B:** This option might seem plausible but is still not accurate. While there is some variation in ultrasound velocity in different tissues, this value does not represent the commonly accepted average.
- **Option D:** This option suggests a much faster speed than the actual average velocity of ultrasound in soft tissues. While ultrasound velocity in bone can be significantly higher, this option does not accurately represent the average velocity in soft tissues.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the velocity of ultrasound in tissues is crucial for accurate imaging and calculation of parameters like distance (e.g., fetal age) and velocity (e.g., blood flow). The average velocity of **1540 m/s** is used in most ultrasound machines as a default setting for calculating these parameters.

## **Correct Answer:** . 1540 m/s