Final answer:
The question deals with the physics concept of intensity of waves, specifically how distance and angle affect it. Intensity is defined as power per unit area and drops according to the inverse square law with distance. For intensity reduction at an angle, the equation I = I₀ cos²(θ) is used.
Step-by-step explanation:
The question relates to the concept of intensity in a physics context, specifically dealing with waves and their propagation. Intensity is defined as the power per unit area carried by a wave. The SI unit for intensity is watts per square meter (W/m²). If a speaker emits sound uniformly in all directions, the intensity of the sound can be calculated using the formula I = P/A, where P is the power and A is the area over which the power is distributed.
When we are considering a change in intensity due to distance, we can apply the inverse square law. For example, if you move twice as far away from the source of the sound, the intensity will drop to one fourth its original value because distance impacts intensity according to the inverse of the square of the distance. In practical terms, if the original intensity at a specific distance is known, you can find the distance at which the intensity will be a certain fraction of the original by applying the inverse square law.
In the context of the question, to find the angle where the intensity is reduced by 90%, thus making it 10% of the initial intensity, the equation I = I₀ cos²(θ) can be used if the wave propagation follows a law where intensity varies with the cosine squared of the angle. Here, I₀ represents the initial intensity, I represents the reduced intensity, and θ represents the angle in question.