# properties of electromagnetic waves

## speed of electromagnetic waves

All electromagnetic waves travel at the same speed through empty space. That speed, called the speed of light, is about 300 million meters per second (3.0 x 108 m/s). Nothing else in the universe is known to travel this fast. The sun is about 150 million kilometers (93 million miles) from Earth, but it takes electromagnetic radiation only 8 minutes to reach Earth from the sun. If you could move that fast, you would be able to travel around Earth 7.5 times in just 1 second!

## speed wavelength and frequency

The speed of a wave is a product of its wavelength and frequency. Because all electromagnetic waves travel at the same speed through space, a wave with a shorter wavelength must have a higher frequency, and vice versa. This relationship is represented by the equation: Speed = Wavelength Frequency The equation for wave speed can be rewritten as: Speed Speed Frequency = Wavelength or Wavelength = Frequency Therefore, if either wavelength or frequency is known, the missing value can be calculated. Consider an electromag- netic wave that has a wavelength of 3 meters. Its speed, like the speed of all electromagnetic waves, is 3.0 108 meters per second. Its frequency can be found by substituting these values into the frequency equation: Frequency = 3.0108 m/s 3.0 m = 1.0 108 waves/s, or 1.0 108 Hz Q: What is the wavelength of an electromagnetic wave that has a frequency of 3.0 108 hertz? A: Use the wavelength equation: Wavelength = 3.0108 m/s 3.0108 waves/s = 1.0 m

## wavelength and frequency of electromagnetic waves

Although all electromagnetic waves travel at the same speed across space, they may differ in their wavelengths, frequencies, and energy levels. Wavelength is the distance between corresponding points of adjacent waves (see the Figure 1.1). Wavelengths of electromagnetic waves range from longer than a soccer field to shorter than the diameter of an atom. Wave frequency is the number of waves that pass a fixed point in a given amount of time. Frequencies of electromagnetic waves range from thousands of waves per second to trillions of waves per second. The energy of electromagnetic waves depends on their frequency. Low-frequency waves have little energy and are normally harmless. High-frequency waves have a lot of energy and are potentially very harmful. Q: Which electromagnetic waves do you think have higher frequencies: visible light or X rays? A: X rays are harmful but visible light is harmless, so you can infer that X rays have higher frequencies than visible light.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

properties of electromagnetic waves include

``````a) speed.

b) frequency.

c) wavelength.

-->  d) all of the above
``````

all electromagnetic waves travel at the same speed through space.

``````-->  a. true

b. false
``````

higher-frequency electromagnetic waves have less energy.

``````a. true

-->  b. false
``````

some electromagnetic waves have wavelengths shorter than the diameter of an atom.

``````-->  a. true

b. false
``````

all electromagnetic waves have frequencies of less than 1000 waves per second.

``````a. true

-->  b. false
``````

the highest-frequency electromagnetic waves

``````a) include visible light.

-->  b) are harmful.

c) have the longest wavelengths.

d) two of the above
``````

which equation shows the relationship of wave speed to wavelength and wave frequency?

``````-->  a) speed = wavelength x frequency

b) speed = wavelength/frequency

c) speed = frequency/wavelength

d) none of the above
``````

## diagram questions

No diagram questions associated with this lesson