Waves, Light, and Optics

An ultrasound probe glides across a patient’s abdomen, sending high-frequency pulses through tissue to reveal the beating heart of a fetus. In the adjacent trauma bay, an X-ray exposes the jagged architecture of a fractured femur, while a pulse oximeter uses a tiny beam of red light to instantly measure oxygen saturation. Every one of these indispensable clinical tools relies upon a single, fundamental physical phenomenon: the wave. A wave is a physical disturbance that transfers energy from one location to another without transferring matter. When you observe a pulse traveling along an artery or hear a heartbeat through a stethoscope, you are not witnessing the physical transport of biological material from the chest to your ears; you are perceiving the pure transmission of energy.

To master the physics of waves for the HESI A2 exam, we must understand how these physical disturbances operate, how they differ, and how they interact with the physical world. Let us dismantle the mechanics of waves, sound, and light.