In echolocation, you use wave sounds to found objects:
A source emanates a wave of sound, and the sound travels in the medium, eventually rebounds on a wall or something, and the wave returns to the source. Then the source is listening the echoes of the sound ( this is the motive of the name)
Now, if some object is between the walls and the source, then when the wave reaches that object, a small part of the wave will rebound first than the rest of it, and the thing using echolocation will know that there is an object and the exact position of the object.
This is something that some animals use to move in dark places, for example the bats use echolocation when they do that little noises in caves.
The speed of sound is taken as 1500 m/s
The length of the fetus is 1.6 cm long
The condition is that the wavelength used must be at most 1/4 of the size of the object that is to be imaged.
For this 1.6 cm baby, the wavelength must not exceed
λ = of 1.6 cm = x 1.6 cm = 0.4 cm =
0.4 cm = 0.004 m this is the wavelength of the required ultrasonic sound.
we know that
v = λf
where v is the speed of a wave
λ is the wavelength of the wave
f is the frequency of the wave
f = v/λ
substituting values, we have
f = 1500/0.004 = 375000 Hz
==> 375000/1000 = 375 kHz ≅ 380 kHz
A) A. 380 kHz
To clerly see the image of the fetus, the wavelength of the ultrasound must be 1/4 of the size of the fetus, therefore
The frequency of a wave is given by
v is the speed of the wave
is the wavelength
For the ultrasound wave in this problem, we have
v = 1500 m/s is the wave speed
is the wavelength
So, the frequency is
B) B. f(c+v)/c−v
The formula for the Doppler effect is:
f' is the apparent frequency
v is the speed of the wave
is the velocity of the receiver (positive if the receiver is moving towards the source, negative if it is moving away from the source)
is the speed of the source (positive if the source is moving away from the receiver, negative if it is moving towards the receiver)
f is the original frequency
In this problem, we have two situations:
- at first, the ultrasound waves reach the blood cells (the receiver) which are moving towards the source with speed
- then, the reflected waves is "emitted" by the blood cells (the source) which are moving towards the source with speed
v = c = speed of sound in the blood
So the formula becomes
C. A. The gel has a density similar to that of skin, so very little of the incident ultrasonic wave is lost by reflection
The reflection coefficient is
where Z1 and Z2 are the acoustic impedances of the two mediums, and R represents the fraction of the wave that is reflected back. The acoustic impedance Z is directly proportional to the density of the medium, .
In order for the ultrasound to pass through the skin, Z1 and Z2 must be as close as possible: therefore, a gel with density similar to that of skin is applied, in order to make the two acoustic impedances Z1 and Z2 as close as possible, so that R becomes close to zero.
d. all of the above
The bats are the only mammals that have managed to perfect flight. They have managed to develop wings, but have started to have a nocturnal life, so in order to be more effective, they have developed their senses like the smell and hearing better, and also developed something new, echolocation. Because the eyesight was not really needed, the bats became almost blind, having very bad eyesight. The echolocation replaced their eyesight though, and it has proven as a very effective adaptation. It is an adaptation that manages to locate objects, food source, be it insects or flowering plants, as well as caves for shelter from predators and cold weather.
Bats use echolocation to
navigate when hunting. foraging for food, and looking for places to roost.
The answer is d. all of the above. Bats use echolocation, a high-frequency system, to fly around and to hunt. Echolocation helps them to hunt insects in flight, to locate flowering plants, and to find warm places for hibernation. Bats' call is pitched at a very high frequency (up to 110 kHz) that are too high for humans to hear.
The correct answer is option D
Echolocation can be defined as the technique by which the bats use sound to locate the places or objects. It is the active use of sonar to locate the insects for hunting in flight during the night time.
Bats also use this technique to locate the places needed for hibernation during the time they are not active and also for locating the flowering plants.