A light beam is said to be what when there is a lack of cohesion, connection, or harmony?

• A. Coherent
• B. Incoherent
• C. Differential
• D. Uniform

Answer: (B)

Coherence is about how well the waves in a light beam stay in step with each other in phase and frequency. When the waves maintain a fixed phase relationship, the beam is coherent; when that relationship breaks down, the beam is incoherent. The phrase “lack of cohesion, connection, or harmony” describes this loss of phase alignment, so the light is incoherent. Incoherent light, like sunlight or lamp light, has many different wavelengths and random phases, so it doesn’t produce stable interference patterns. In contrast, coherent light (such as from a laser) has waves that stay in step, yielding clear interference. The other terms don’t capture the idea of phase relationship: differential isn’t a standard descriptor for coherence, and uniform refers to intensity distribution, not the phase connection.