3. (12) (a) Sonar is used for commercial fishing to detect schools of fish which have internal air sacks. Assume that the sonar is generated with a power of 0.18 W at 50 kHz that spreads in a 35o cone as it propagates into water. If 18% of the sound energy reaching the school of fish is reflected and scattered uniformly, calculate the power density reaching the school of fish, and the power density reflected from the fish at 55 meters. (Attenuation in water at 50 kHz is 13 dB/km.) (3) (b) What would happen to the power density of the sonar reflected from the fish at 55 m, if the frequency of the sound waves were increased by 10%

Follow these directions and answer the questions. 1. set up the ripple tank as in previous investigations. 2. bend the rubber tube to form a "concave mirror" and place in the ripple tank. the water level must be below the top of the hose. 3. generate a few straight pulses with the dowel and observe the reflected waves. do the waves focus (come together) upon reflection? can you locate the place where the waves meet? 4. touch the water surface where the waves converged. what happens to the reflected wave? 5. move your finger twice that distance from the hose (2f = c of c, center of the curvature) and touch the water again. does the image (the reflected wave) appear in the same location (c of c)? you may have to experiment before you find the exact location. sometimes it is hard to visualize with the ripple tank because the waves move so quickly. likewise, it is impossible to "see" light waves because they have such small wavelengths and move at the speed of light. however, both are examples of transverse waves and behave in the same way when a parallel wave fronts hit a curved surface.

True or false: the revolution of the earth creates day and night as it rotates around the sun

This punnett square shows the cross between two pants. one parent has round seeds (rr). and the other parent has wrinkled seeds (rr) which best describes their offspring as shown in this cross?