Ch 15 WS Answers

Physical Science

Chapter 15

WS Characteristics of Waves

1.    Define Wave: A disturbance that transfers energy from place to place

2.    What is the difference between a mechanical wave and an electromagnetic wave?  The mechanical wave must have a medium to pass through, but the electromagnetic does not need a medium.

3.    Give an example of each:  Mech = sound wave;  Electromagnetic = light wave

4.    Draw a wave and label the following parts: crest, trough, amplitude, frequency, wavelength

(see our notes)

5.    Define the following

·                  Amplitude - the distance from the center line to the crest

·                  Frequency - the amount of crests to pass through a certain point per second

·                  Wavelength - the distance from crest to crest

6.    Label the following as transverse or longitudinal waves:

7.    Do compression and rarefaction occur in transverse or longitudinal waves? Circle 3 compression sections in the image above. (see where compression is labeled above)

8.  We learned one law of waves.  It states that the speed of a wave will stay constant as long as the wave ____continues to go through the same medium_________.

9.   Does the law from #8 explain why music sounds different when you are underwater and the music is above water? yes

10.          What happens when a wave hits a medium that it cannot pass through? Give me the scientific word.  Reflection

11.         What happens when a wave hits a new (passable) medium at an angle?  Give me the scientific word.  Diffraction

12.         Give an example from everyday life when you have seen this happen.  In class we put a pencil in water and saw how it appears to be bent under the water.  This is caused by the light waves bending as they pass through a new medium (water to glass to air).

13.          If two waves hit each other (interference), there are two possible occurrences.  What are they?

a.   constructive interference

b.   destructive interference

15.         Which of the two interferences will make the new wave have twice the amplitude? constructive

16.         Interference sometimes leads to resonance.  Give one example of resonance.

•  a crystal glass breaking when a singer hits a note with the same frequency
• a building falling when an earthquake causes the dirt to have the same frequency as the building
• a bridge falling when the wind passing it has the same frequency

17.         EARTHQUAKES!!  Seismic waves are both transverse and longitudinal. They each travel differently through the Earth.  Which of the two can be felt on the opposite side of our planet when there is an earthquake?  Longitudinal

18.         Why can’t the other one be felt on the other side of the Earth?  Because transverse waves cannot travel through a liquid and at least part of the Earth's core is a liquid.

19.         What does this tell us about the Earth’s core?  At least part of it is a liquid

20.           Seismic waves are called   S  or P  waves.  Which one is the longitudinal wave?   P

21.           A surface wave is another type of seismic wave.  These are very destructive and occur when____P  or  S  waves reach the surface_________.

22.           We detect earthquakes using a ____seismograph_____ and if we use 3 of these instruments we can determine the ____location__ of the earthquake.

23.         What is one other use for a seismograph and waves?  It can be used to detect underground resources such as oil or water.