Understanding waves and wavelengths

Waves appear in many different forms. Seismic waves shake the ground during earthquakes. Light waves travel across the universe, allowing us to see distant stars. And every sound we hear is a wave. So what do all these different waves have in common?

A wave is a disturbance that moves energy from one place to another. Only energy —  not matter — is transferred as a wave moves.

The substance that a wave moves through is called the medium. That medium moves back and forth repeatedly, returning to its original position. But the wave travels along the medium. It does not stay in one place.

Imagine holding one end of a piece of rope. If you shake it up and down, you create a wave, with the rope as your medium. When your hand moves up, you create a high point, or crest. As your hand moves down, you create a low point, or trough (TRAWF). The piece of rope touching your hand doesn’t move away from your hand. But the crests and troughs do move away from your hand as the wave travels along the rope. 

In this wave, blue particles move up and down, passing through the line in the center. Some waves in nature behave like this, too. For example, in the ocean, the water moves up and down, but returns to surface level. This creates high points called crests and low points called troughs. As the water moves up and down, the crests and troughs move to the side, carrying energy.J. LOOK

The same thing happens in other waves. If you jump in a puddle, your foot pushes on the water in one spot. This starts a small wave. The water that your foot hits moves outward, pushing on the water nearby. This movement creates empty space near your foot, pulling water back inwards. The water oscillates, moving back and forth, creating crests and troughs. The wave then ripples across the puddle. The water that splashes at the edge is a different bit of water than where your foot made contact. The energy from your jump moved across the puddle, but the matter (the molecules of water) only rocked back and forth.

Light, or electromagnetic radiation, also can be described as a wave. The energy of light travels through a medium called an electromagnetic field. This field exists everywhere in the universe. It oscillates when energy disturbs it, just like the rope moves up and down as someone shakes it. Unlike a wave in water or a sound wave in air, light waves don’t need a physical substance to travel through. They can cross empty space because their medium does not involve physical matter. 

Scientists Say: Wavelength

Scientists use several properties to measure and describe all these types of waves. Wavelength is the distance from one point on a wave to an identical point on the next, such as from crest to crest or from trough to trough. Waves can come in a wide range of lengths. The wavelength for an ocean wave might be around 120 meters (394 feet). But a typical microwave oven generates waves just 0.12 meter (5 inches) long. Visible light and some other types of electromagnetic radiation have far tinier wavelengths.  

Scientists Say: Hertz

Frequency describes how many waves pass one point during one second. The units for frequency are hertz. Traveling through the air, a music note with a frequency of 261.6 hertz (middle C) pushes air molecules back and forth 261.6 times every second. 

Scientists Say: Frequency

Frequency and wavelength are related to the amount of energy a wave has. For example, when making waves on a rope, it takes more energy to make a higher frequency wave. Moving your hand up and down 10 times per second (10 hertz) requires more energy than moving your hand only once per second (1 hertz). And those 10 hertz waves on the rope have a shorter wavelength than ones at 1 hertz. 

Many researchers rely on the properties and behavior of waves for their work. That includes astronomers, geologists and sound engineers. For example, scientists can use tools that capture reflected sound, light or radio waves to map places or objects. 

electromagnetic spectrum
For light in the electromagnetic spectrum, wavelengths can range from very long (kilometers-long for radio waves) to very small (a millionth of a millionth of a meter for gamma rays). The ruler shows how long these electromagnetic waves are in meters or fractions of a meter. Human eyes can see only a very small portion of these waves.

Power Words

astronomer: A scientist who works in the field of research that deals with celestial objects, space and the physical universe.

behavior: The way something, often a person or other organism, acts towards others, or conducts itself.

crest: The highest part of a hill, a mountain or a swell of water. (in physics) The top, or highest point, in a wave.

earthquake: A sudden and sometimes violent shaking of the ground, sometimes causing great destruction, as a result of movements within Earth’s crust or of volcanic action.

electromagnetic radiation: Energy that travels as a wave, including forms of light. Electromagnetic radiation is typically classified by its wavelength. The spectrum of electromagnetic radiation ranges from radio waves to gamma rays. It also includes microwaves and visible light.

engineer: A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.

frequency: The number of times some periodic phenomenon occurs within a specified time interval. (In physics) The number of wavelengths that occurs over a particular interval of time.

gamma rays: High-energy radiation often generated by processes in and around exploding stars. Gamma rays are the most energetic form of light.

hertz: The frequency with which something (such as a wavelength) occurs, measured in the number of times the cycle repeats during each second of time.

matter: Something that occupies space and has mass. Anything on Earth with matter will have a property described as “weight.”

oscillate: To swing back and forth with a steady, uninterrupted rhythm.

radiation: (in physics) One of the three major ways that energy is transferred. (The other two are conduction and convection.) In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space.

radio waves: Waves in a part of the electromagnetic spectrum. They are a type that people now use for long-distance communication. Longer than the waves of visible light, radio waves are used to transmit radio and television signals. They also are used in radar.

range: The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists.

seismic wave: A wave traveling through the ground produced by an earthquake or some other means.

sound wave: A wave that transmits sound. Sound waves have alternating swaths of high and low pressure.

trough: (in physics) the bottom or low point in a wave.

universe: The entire cosmos: All things that exist throughout space and time. It has been expanding since its formation during an event known as the Big Bang, some 13.8 billion years ago (give or take a few hundred million years).

wave: A disturbance or variation that travels through space and matter in a regular, oscillating fashion.

wavelength: The distance between one peak and the next in a series of waves, or the distance between one trough and the next. It’s also one of the “yardsticks” used to measure radiation. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.

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