1. Electromagnetic Spectrum
Identify and explain how different parts of the electromagnetic spectrum are used

2. Electromagnetic Spectrum

3. Electromagnetic Spectrum
Here are the different types of radiation in the EM spectrum, in order from lowest energy to highest:

4. Radio waves
have the longest wavelength in the electromagnetic spectrum.
These waves carry the news, ball games, and music you listen to on the radio.
They also carry signals to television sets and cellular phones.

5. Microwaves
Have shorter wavelengths than radio waves, which heat the food we eat.
They are also used for radar images, like the Doppler radar used in weather forecasts.

6. infrared waves with long wavelengths and short wavelengths.
Infrared waves with long wavelengths can be detected as heat.
Heat Lamps give off these long infrared waves.
We call these thermal infrared or far infrared waves.
The sun gives off infrared waves with shorter wavelengths.

7. Visible light waves are the only electromagnetic waves we can see.
We see these waves as the colors of the rainbow.
Each color has a different wavelength.
Red has the longest wavelength and violet has the shortest wavelength.
These waves combine to make white light.

8. Ultraviolet waves have wavelengths shorter than visible light waves.
These waves are invisible to the human eye, but some insects can see them.
Of the sun's light, the ultraviolet waves are responsible for causing our sunburns.

9. X-Rays: As wavelengths get smaller, the waves have more energy.
X-Rays have smaller wavelengths and therefore more energy than the ultraviolet waves.
X-Rays are so powerful that they pass easily through the skin allowing doctors to look at our bones.

10. Cosmic Rays
are high energy charged particles, originating in outer space, that travel at nearly the speed of light and strike the Earth from all directions.
Aurora Borealis: Northern Lights Auroras are associated with the solar wind, a flow of ions continuously flowing outward from the Sun.

11. Gamma Rays
have the smallest wavelength and the most energy of the waves in the electromagnetic spectrum.
These waves are generated by radioactive atoms and in nuclear explosions.
Gamma rays can kill living cells, but doctors can use gamma rays to kill diseased cells.

12. Science and the
Scientific Method

13. What is science?
1. Science deals only with the natural world.
2. Scientists collect and organize information in a careful, orderly way, looking for patterns and connections between events.
3. Scientists propose explanations that can be tested by examining evidence.
4. Science is an organized way of using evidence to learn about the natural world.
The goal of science is to investigate and understand the natural world, to explain events in the natural world, and to use those explanations to make useful predictions.

14. How is Science Done? Science begins with an observation.
This is the process of gathering information about events or processes in a careful, orderly way.
Data is the information gathered from making observations.
There are two types of data:
Quantitative data are: numbers and are obtained by counting or measuring.
Qualitative data are: descriptions and involve characteristics that cannot be counted.

15. A hypothesis is a scientific explanation for a set of observations.
A hypothesis must be stated in a way that makes it “testable”. The hypothesis is just a possible answer to a question, and it must be thoroughly tested.
Hypothesis

16. The scientific method Step 1: Observation / Asking a Question
A problem or a question must first be identified.
How much water can a root hair absorb?
Why does a plant stem bend toward the light?
What effect does temperature have on heart rate?
Step 2: Form a Hypothesis
A possible explanation to the question or problem.
It is simply a prediction and has not yet been proven or disproven.
It must be stated in a way that is testable.
A statement is considered “testable” if evidence can be collected that either does or does not support it.

17. Step 3: Designing a Controlled Experiment
The factors in an experiment that can be changed are called variables. Some example of variables would be: changing the temperature, the amount of light present, time, concentration of solutions used.
A controlled experiment works with one variable at a time. If several variables were changed at the same time, the scientist would not know which variable was responsible for the observed results.
In a “controlled experiment” only one variable is changed at a time. All other variables should be unchanged or “controlled”.
An experiment is based on the comparison between a ____________ with an ________________.
a) These two groups are identical except for one factor.
b) The control group serves as the comparison. It is the same as the experiment group, except that the one variable that is being tested is removed.
c) The experimental group shows the effect of the variable that is being tested.

18. There are two variables in an experiment:
a) The independent variable is the variable that is deliberately changed by the scientist.
b) The dependent variable is the one observed during the experiment. The dependent variable is the data we collect during the experiment. This data is collected as a result of changing the independent variable.

19. Step 4: Recording and Analyzing Results
1. The data that has been collected must be organized and analyzed to determine whether the data are reliable.

20. Step 5: Drawing Conclusions
The evidence from the experiment is used to determine if the hypothesis is proven or disproven.
Experiments must be repeated over and over. When repeated, the results should always be the same before a valid conclusion can be reached.

21. Forming a Theory
A theory may be formed after the hypothesis has been tested many times and is supported by much evidence.
THEORY: A broad and comprehensive statement of what is thought to be true.
It is supported by considerable evidence.

22. Waves and Wave Properties
Presentation for lesson 2: Waves and Wave Properties, in the Waves: The Three Color Mystery unit
The slides are animated so you can click (space bar, mouse, etc.) to show the next item when the class is ready.
Waves and Wave Properties

23. Why are we able to see?
Answer: Because there is light.
And…what is light?
Answer: Light is a wave.
So…what is a wave?

24. Answer: A wave is a disturbance that carries energy from place to place.
A wave does NOT carry matter with it! It just moves the matter as it goes through it.
Think of a stadium wave: the people are moving up and down, but the wave goes around the stadium

25. Some waves do not need matter (called a “medium”) to be able to move (for example, through space).
These are called electromagnetic waves (or EM waves).
Some waves MUST have a medium in order to move. These are called mechanical waves.

26. Wave Types
Transverse waves: Waves in which the medium moves at right angles to the direction of the wave

27. Parts of transverse waves:
Crest: the highest point of the wave
Trough: the lowest point of the wave

28. Compressional (or longitudinal) waves: Waves in which the medium moves back and forth in the same direction as the wave

29. Parts of longitudinal waves:
Compression: where the particles are close together
Rarefaction: where the particles are spread apart

30. Wave properties depend on what (type of energy) is making the waves.
Wavelength: The distance between one point on a wave and the exact same place on the next wave.

31. The higher the frequency, the more energy in the wave.
2. Frequency: How many waves go past a point in one second; unit of measurement is hertz (Hz).
The higher the frequency, the more energy in the wave.
10 waves going past in 1 second = 10 Hz
1,000 waves go past in 1 second = 1,000 Hz
1 million waves going past = 1 million Hz

32. 3. Amplitude: How far the medium moves from rest position (where it is when not moving).
Remember that for transverse waves, the highest point is the crest, and the lowest point is the trough.

33. Remember that for compressional waves, the points where the medium is close together are called compressions and the areas where the medium is spread apart are called rarefactions.
The closer together and further apart the particles are, the larger the amplitude.
compression
rarefaction

34. The energy of a wave is proportional to the square of its amplitude
The energy of a wave is proportional to the square of its amplitude. Mathematically speaking . . .
E = CA2
Where:
E = energy (the capacity to do work)
C = a constant (depends on the medium)
A = amplitude
For example:
If the amplitude is equal to 3 units
(and we assume C = 1 for this case) . . .
E = (1) (3)2 = (1) (9) = 9 units

35. Note that when the amplitude of a wave is one unit, the energy is one unit.
When the amplitude is doubled, the energy is quadrupled.
When the energy is 10 times greater, the energy is 100 times greater!
Amplitude
Energy 1 2 4 3 9 16 5 25 6 36 7 49 8 64 81 10
100
E = CA2

36. A mathematical way to calculate speed:
4. Wave speed: Depends on the medium in which the wave is traveling. It varies in solids, liquids and gases.
A mathematical way to calculate speed:
wave speed = wavelength x frequency
(in meters)
(in Hz) OR
v = f x ג
Problem: If a wave has a wavelength of 2 m and a frequency of 500 Hz, what is its speed?
Answer: speed = 2 m x 500 Hz = 1000 m/s

37. Changing Wave Direction
Answer: speed = 2 m x 500 Hz = 1000 m/s
Changing Wave Direction
Reflection: When waves bounce off a surface.
If the surface is flat, the angle at which the wave hits the surface will be the same as the angle at which it leaves the surface (angle in = angle out).
This is the law of reflection.
For example, think of a pool ball striking the side of the pool table: The angle it hits the side is the same angle it bounces off the side.

38. 2. Refraction: Waves can bend.
This happens when a wave enters a new medium and its SPEED CHANGES.
The amount of bending depends on the medium it is entering.

39. 3. Diffraction: The bending of waves AROUND an object.
The amount of bending depends on the size of the obstacle and the size of the waves.
Large obstacle, small wavelength = low diffraction
Small obstacle, large wavelength = large diffraction