What is the requirement for transmission?

• A. Oblique incidence
• B. The use of the law of conservation of energy
• C. Reflection information
• D. Equal speeds

Answer: (B)

The main idea is energy conservation in wave transmission across an interface. When a wave hits a boundary between two media, some energy is transmitted into the second medium and some may be reflected back, with any leftover energy possibly absorbed by the boundary. The fundamental rule is that energy must balance: the incident energy equals the transmitted energy plus the reflected energy (plus any absorbed energy in a real, non-ideal boundary). So ensuring this energy balance is what enables transmission to occur in the first place.

The angle of incidence or the distribution between transmitted and reflected energy depends on boundary properties, but these factors don’t create or destroy energy. Equal speeds aren’t required for transmission; they just influence how much energy is reflected versus transmitted in a given situation.