The clocktower ("ghantaghar") of Dehradun is famous for the sound of its bell, which can be heard, albeit faintly, upto the outskirts of the city 8   km away. Let the intensity of this faint sound be 30   dB . The clock is situated 80   m high. The intensity at the base of the tower is:-

Step-by-step solution

r 2 = 80   m ,      L 2 = ? r 1 = 8000   m ,   L 1 = 30   dB L = 10 log 10 I I 0 Intensity due to a point source, I ∝ 1 r 2 L 2 - L 1 = 10 log 10 I 2 I 0 - 10 log 10 I 1 I 0 L 2 - L 1 = 10 log 10 I 2 I 1 = 10 log 10 r 1 2 r 2 2 L 2 - 30 = 10 log 10 10 4 = 40   L 2 = 70   dB