§5.7 Echo, questions and answers

• Natuurkunde / Scheikunde
• Middelbare school

§5.7 Echo — answers

1) What is an echo? How does it work? Explain.

When a sound repeats because it bounces back. 

2)What is ultra sound? 

3) What do we use ultra sound for?

Sound waves with a frequency higher that 20000 Hz, which means of a frequency higher than humans are able to hear.

Ultrasound is used for echolocation, and to create a 3d image of someones body, such as their vein system or a growing baby still in the womb.

4) 

a. What is echolocation and how does it work? 

b. Give three examples where echolocation is used (you may inclde animals that use it).

By measuring the time between a sound being produced and the dection of the echo it can be calculated how far away an object is. This way objects can be dected that can't be seen, such as an object on the bottom of the sea. 

A submarine, dolphins, whales bats

6) Little brown bats use echolocation, but megabats don't. Why do little brown bats have an advantage over megabats when it comes to living in caves?

Despite it being drak in the cave, the little brown bat will still be able to know where the cave walls are since it uses sound to create an image of the room it is in. The mega bat won't be able to see anything in a dark cave.

Little brown bat

Megabat

7) Most submarines have powerful lamps. Why do they still require echolocation to detect objects such as wercked ships?

Since the sea is very dark, echolocation allows a submarine to creat an image of it's surrounding without it being able to see anything.

8) Why are the walls in the theater designed to absorb sound?

9) How do you call the effect of echoes effecting the sound of the original source of their sound?

So that the sound of the preformance in the theater doesn't get distorted by the sound of echoes.

Reverberation

The dutch prime minister is standing in a mountain valley and wants to know how far away the closest mountain to him is. He hits two wooden planks together, producing a loud sound. 5 seconds later he hears the echo. How far away is the mountain closest to him?

Given:

t = 5s

v = 343 m/s (speed of sound)

Asked

How far away is the mountain closest to him?

Formula

v = 2s/t     s = (v*t)/2

Calculation

s = (5 * 343)/2 = 857.5 m

Answer

The mountain closest to Mr. Rutte is 857 meters away from him. 

A group of hikers walking through a forest finds a cave. One of the hikers makes a loud yell, a moment later an echo comes back. The cave is 500 meters deep. How long does it take before they hear the echo?

Given:

s = 500

v = 343 m/s

Asked
How long does it take before they hear the eacho?

Formula

v = 2s/t     t = 2s/v

Calculation

t = (2*500)/343 = 2.9 s

Answer

It takes 2.9 seconds before they hear the echo.

A whale uses echolocation to detect objects in its surroundings. The whale creates a high pitch sound and 6.6 seconds later he hears an echo coming back. How far away is the object that the whale has detected in km?

Given:

t = 6.6 s

v = 1500 m/s (speed of sound through water)

Asked
How far away is the object the whale dected?

Formula

v = 2s/t     s = (v*s)/2

Calculation

s = (1500 * 6.6)/2 = 4950 m =5 km

Answer

The object the whale has dected is 5 km away.