According to the cosine law, the maximal heating effect occurs when energy strikes tissue at which angle?

According to the cosine law, the maximal heating effect occurs when energy strikes tissue at which angle?

• A. 0 degrees
• B. 90 degrees
• C. 45 degrees
• D. 180 degrees

Answer: (B)

The heating effect is greatest when energy enters the tissue directly, perpendicular to the surface. When the beam hits at a right angle to the tissue surface, most of the energy is delivered into the tissue with minimal reflection, so the energy per unit area inside the tissue is highest. If the energy strikes at a more oblique angle, the energy is spread over a larger surface area and more is reflected at the interface, reducing how much heats the tissue. So energy striking at a right angle to the surface (a 90-degree angle in this framing) produces the maximal heating.

The heating effect is greatest when energy enters the tissue directly, perpendicular to the surface. When the beam hits at a right angle to the tissue surface, most of the energy is delivered into the tissue with minimal reflection, so the energy per unit area inside the tissue is highest. If the energy strikes at a more oblique angle, the energy is spread over a larger surface area and more is reflected at the interface, reducing how much heats the tissue. So energy striking at a right angle to the surface (a 90-degree angle in this framing) produces the maximal heating.