Explain how defects in a metal block can be detected using ultrasound.

Explanation

### Step-by-Step Solution:

1. **Understanding Ultrasound**: Ultrasound refers to sound waves that have a frequency higher than the upper limit of human hearing (20 kHz). These waves can travel through various materials, including metals.

2. **Setting Up the Experiment**: To detect defects in a metal block using ultrasound, we need two main components: an ultrasound wave emitter and a detector. The emitter generates ultrasound waves, while the detector receives them.

3. **Positioning the Equipment**: Place the ultrasound emitter on one side of the metal block and the detector on the opposite side. This setup allows the ultrasound waves to travel through the metal block.

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