Waves and Energy

GK-12 UCLA NSF

Meghedi Babakhanian

●List as many types of waves you can think of.●What do waves transfer?

●In this picture, what is happening to the gravitational potential energy of the drop?

What are Waves?

San Diego Unified School District Physics 1,2 Core Laboratory Activity - Lab 17: Waves

●Sound waves, visible light waves, radio waves, microwaves, water waves, sine waves, cosine waves, stadium waves, earthquake waves, waves on a string, slinky waves  - ALL types of Waves!

●Waves transfer ENERGY!!

●Gravitational potential energy of a water drop turns into kinetic energy, which transfers energy in the form of a WAVE!

What are Waves?

Anatomy of a Wave

CREST

TROUGH

AMPLITUDE

WAVELENGTH

●Transverse

The motion of the medium is at right angles to the direction in which a wave travels

Stretched strings of musical instruments, electromagnetic waves, S-waves in earthquakes

●LongitudinalThe particles of the medium move back and forth in the same direction in which the wave travels Sound waves, P-waves in earthquakes

Two Types of Waves

●What type of wave is an ocean wave?

Waves

Key Terms

●Spherical wave propagation:

Intensity Calculation

area

Power

areatime

Energy

Intensity

24 r

PowerIntensity

●Using voltage:● You see voltage vs. time on

the oscilloscope● You can think of it as sound

wave pressure vs. time.

Intensity Calculation Using Oscilloscope

c

pressureIntensity

2

Effect of temperature on properties of air

Temperature in °C

Speed of soundc in 

m·s−1

Density of airρ in kg·m−3

Acoustic impedanceZ in N·s·m−

3

+35 351.88 1.1455 403.2

+30 349.02 1.1644 406.5

+25 346.13 1.1839 409.4

+20 343.21 1.2041 413.3

+15 340.27 1.2250 416.9

+10 337.31 1.2466 420.5

+5 334.32 1.2690 424.3

0 331.30 1.2922 428.0

−5 328.25 1.3163 432.1

−10 325.18 1.3413 436.1

−15 322.07 1.3673 440.3

−20 318.94 1.3943 444.6

−25 315.77 1.4224 449.1

● ρ (Density of medium) ● c ( speed of medium)● ρ c (air @ room temp 20 °C) = 413.3 N·s·m−3

Conclusion

• We are constantly interacting with waves

• Waves carry energy

• Light and S-waves are examples of transverse waves.

• Sound and P-waves are examples of longitudinal waves.

●Basic function of an oscilloscope: To display voltage vs. time. ● Voltage: usually on the vertical axis ● Time: usually on the horizontal axis.

Oscilloscope

●Display screen of the oscilloscope:● Grid of black lines● Division - Each square in this grid is known as a

“division”. ● Two main things that you will change on the

oscilloscope:● Number of volts that each division represents ● length of time each division represents.

Oscilloscope

● Practice with me: ● Look at the front of oscilloscope and find the knobs that say:

● “Volts/Div” and “Time/Div”.

● Try twisting the knobs and see what happens.

Oscilloscope

●Voltage: ● When you turn the knob on “Volts/Div”, you’re changing

how many ___________each square represents. ● Example: if the setting is 10 Volts/Div, each square

represents _____ V.

●Time:● When you turn the knob on “Time/Div”, you’re changing

how many ___________each square represents. ● Example: If the setting is 1 ms/Div, each square

represents _____ millisecond.

Oscilloscope