Fishing sonar. The attenuation constant for sound waves in water increases with frequency. Consider the sonar used for fishing. The reflection of sound from fish schools is used for sports and commercial fishing. Fish produce relatively large reflections because of their air sack, the reflection being due to the interface between flesh and air, whereas the reflection at the interface between flesh and water is small. The signal is generated by an ultrasound actuator and detected by an ultrasound sensor. Suppose the actuator produces a power of 0.1 W at 50 kHz (a common frequency in fishing sonars) and the power propagates in a relatively narrow beam. Assuming that 20% of the sound reaching a fish school is reflected and that reflected sound is scattered uniformly over a half-sphere, calculate the required sensitivity of the ultrasonic sensor (in W/m2 ) to detect a fish school at a depth of 20 m. Attenuation in water at 50 kHz is 15 dB/km.

this a false

explanation:

a solenoid is created by wrapping a l = 90 m long wire around a hollow tube of diameter d = 4.5 cm.   the wire diameter is d = 0.9 mm.   the solenoid wire is then connected to a power supply so that a current of i = 9 a flows through the wire.

randomized variablesl = 90 m

d = 4.5 cm

d = 0.9 mm

i = 9 a                                          

write an expression for the number of turns, n, in the solenoid. you do not need to take into account the diameter of the wire in this calculation.

calculate the number of turns, n, in the solenoid.

write an expression for the length of the solenoid (l2) in terms of the diameter of the hollow tube d.

calculate the length of the solenoid (l2)   in meters.

calculate the magnitude of the magnetic field at the center of the solenoid in teslas.

explanation:

the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.