Sci: Electromagnetic Waves

Correcting vision

If the eyeball is slightly too long or too short, the image on the retina is out of focus. Fortunately, wearing glasses or contact lenses can correct this type of vision problem. A nearsighted person can see nearby things clearly, but objects at a distance are blurred. The eyeball is too long, so the lens focuses the image in front of the retina. To correct this, a concave lens in front of the eye spreads out light rays before they enter the eye. As a result, the image forms on the retina. A farsighted person can see distant objects clearly, but nearby objects appear blurry. The eyeball is too short, so the image that falls on the retina is out of focus. A convex lens corrects this by bending light rays toward each other before they enter the eye. An image then focuses on the retina.

infrared rays

If you turn on an electric stove's burner, you can feel it warm up before the heating element starts to glow. The invisible heat you feel is infrared radiation, or infrared rays. Infrared rays are electromagnetic waves with wavelengths shorter than those of microwaves. They have higher frequencies and therefore more energy than microwaves. Because you can feel the energy of infrared rays as heat, these rays are often called heat rays. Heat lamps have bulbs that give off mainly infrared rays. They are used to keep things warm, such as food in a cafeteria or young animals in an incubator. Most objects give off some infrared rays. Warmer objects give off infrared rays with more energy and higher frequencies than cooler objects. An infrared camera uses infrared rays instead of visible light to take pictures called thermograms. A thermogram is an image that shows regions of different temperatures in different colors.

Light enters the eye

Light enters the eye through the transparent front surface called the cornea. The cornea protects the eye. It also acts as a lens to help focus light rays. After passing through the cornea, light enters the pupil, the part of the eye that looks black. The pupil is an opening through which light enters the inside of the eye. In dim light, the pupil becomes larger to allow in more light. In bright light, the pupil becomes smaller to allow in less light. The iris is a ring of muscle that contracts and expands to change the size of the pupil. The iris gives the eye its color. In most people the iris is brown; in others it is blue, green, or hazel.

Microwaves

Microwaves have shorter wavelengths and higher frequencies than radio waves do. When you think about microwaves, you probably think of microwave ovens that cook and heat food. But microwaves have many other uses, including cellular phone communication and radar. Radar stands for radio detection and ranging. Radar is a system that uses reflected microwaves to detect objects and measure their distance and speed. To measure distance, a radar device sends out microwaves that reflect off an object. The time it takes for the reflected waves to return is used to calculate the object's distance. To measure speed, a radar device uses the Doppler effect. For example, suppose a police radar gun sends out microwaves that reflect off a car. Because the car is moving, the frequency of the reflected waves is different from the frequency of the original waves. The difference in frequency is used to calculate the car's speed.

whats the particle model of light?

Sometimes light behaves like a stream of particles. For example, when a beam of high frequency light shines on some metals, it causes tiny particles to move. These particles are called electrons. Sometimes light can even cause an electron to move so much that it is knocked out of the metal, as shown in Figure 3. This is called the photoelectric effect. This effect can be explained by thinking of light as a stream of tiny packets, or particles, of energy. Each packet of light energy is called a photon. For the effect to occur, each photon must contain enough energy to knock an electron free from the metal.

THE HIGHER THE FREQUENCY OF A WAVE, THE HIGHER ITS ENERGY.

THE HIGHER THE FREQUENCY OF A WAVE, THE HIGHER ITS ENERGY.

energy

The energy that electromagnetic waves transfer through matter or space is called electromagnetic radiation. Electromagnetic waves do not require a medium such as air, so they can transfer energy through a vacuum, or empty space.

how do you see objects?

The eye is a complex structure with many parts. Each part plays a role in vision. ✰You see objects when a process occurs that involves both your eyes and your brain.

A signal goes to the brain

The rods and cones send signals to the brain along a short, thick nerve called the optic nerve. The optic nerve begins at the blind spot, an area of the retina that has no rods or cones. Your brain interprets the signals from the optic nerve as an upright image. It also combines the two images from your eyes into a single three-dimensional image.

what makes up the electromagnetic spectrum?

There are many different types of electromagnetic waves. The complete range of electromagnetic waves placed in order of increasing frequency is called the electromagnetic spectrum. ✰The electromagnetic spectrum is made up of radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X-rays, and gamma rays.

what are the types of electromagnetic waves?

There are radio waves, microwaves, infrared rays, visible light, ultraviolet rays, and tiny amounts of X-rays and gamma rays. These waves are all electromagnetic waves.

why does the size of the pupil change?

To allow more or less light to enter the eye.

Why does a dentist cover you with a lead apron to take X-rays of your teeth?

To protect your bones from X-rays.

what's the wave model of light?

When light passes through a polarizing filter, it has the properties of a wave. An ordinary beam of light consists of waves that vibrate in all directions. A polarizing filter acts as though it has tiny slits aligned in only one direction. The slits can be horizontal or vertical. When light enters a polarizing filter, only some waves can pass through it. The light that passes through is called polarized light. To help you understand the wave model, think of light waves like transverse waves on a rope. They vibrate in all directions. If you shake a rope through a fence with vertical slits, only waves that vibrate up and down will pass through. The other waves are blocked. A polarizing filter acts like the slits in a fence. It allows only waves that vibrate in one direction to pass through it.

how does a rainbow form?

white light from the sun is refracted by raindrops into the spectrum.

What Models Explain How Electromagnetic Waves Behave?

✰Two different models are needed to explain the behavior of electromagnetic waves. A wave model best explains many of the behaviors, but a particle model best explains others. Light is an electromagnetic wave. It has many properties of waves but can also act as though it is a stream of particles.

An image forms

After entering the pupil, the light passes through the lens. The lens is a convex lens that refracts light to form an image on the lining of your eyeball. Muscles, called ciliary muscles, hold the lens in place behind the pupil. When you focus on a distant object, the ciliary muscles relax, and the lens becomes longer and thinner. When you focus on a nearby object, the muscles contract, and the lens becomes shorter and fatter. When the cornea and the lens refract light, an upside-down image is formed on the retina. The retina is a layer of cells that lines the inside of the eyeball. Rods are cells that contain a pigment that responds to small amounts of light. The rods allow, you to see in dim light. Cones are cells that respond to color. They may detect red light, green light, or blue light. Cones respond best in bright light. Both rods and cones help change images on the retina into signals that then travel to the brain.

what are the characteristics of electromagnetic waves?

An electromagnetic wave is a transverse wave that involves the transfer of electric and magnetic energy. ✰An electromagnetic wave is made up of vibrating electric and magnetic fields that move through space or some medium at the speed of light. An electromagnetic wave can begin with the movement of charged particles, all of which have electric fields around them. As the particles change speed or direction, a vibrating electric field is created, which in turn produces a vibrating magnetic field. The vibrating magnetic field creates a vibrating electric field. The electric and magnetic fields produce each other repeatedly. The result is an electromagnetic wave.

how fast does an electromagnetic wave travel through space at the speed of light?

An electromagnetic wave travels through space at the speed of light at about 300,000 kilometers per second.

how do electromagnetic waves compare?

Can you imagine trying to take a photo with a radio or heating your food with X-rays? Light, radio waves, and X-rays are all electromagnetic waves. But each has properties that make it more useful for some purposes than others. ✰All electromagnetic waves travel at the same speed in a vacuum, but they have different wavelengths and different frequencies. A vacuum is a space that contains no air or other gas. Visible light is the only range of wavelengths your eyes can see. Your radio detects radio waves, which have much longer wavelengths than visible light. X-rays, on the other hand, have much shorter wavelengths than visible light. For waves in any medium, as the wavelength decreases, the frequency increases. Waves with the longest wavelengths have the lowest frequencies. Waves with the shortest wavelengths have the highest frequencies. The higher the frequency of a wave, the higher its energy.

visible light

Electromagnetic waves that you can see are called visible light. They make up only a small part of the electromagnetic spectrum. Visible light waves have shorter wavelengths and higher frequencies than infrared rays. Visible light that appears white is actually a mixture of many colors. Recall that light waves bend, or refract, when they enter a new medium. So, when white light passes through rain drops, a rainbow can result.

radio waves

Electromagnetic waves with the longest wavelengths and the lowest frequencies are radio waves. Radio waves are used in broadcasting to carry signals for radio programs. A broadcast station sends out radio waves at certain frequencies. Your radio picks up the radio waves and converts them into an electrical signal. The electrical signal is then converted into sound.

Gamma rays

Electromagnetic waves with the shortest wavelengths and highest frequencies are gamma rays. Since they have the greatest amount of energy, gamma rays are the most penetrating of electromagnetic waves. Because of their penetrating ability, these rays are used to examine the body's internal structures. A patient can be injected with a fluid that emits gamma rays. Then, a gamma-ray detector can form an image of the inside of the body. Some radioactive substances and certain nuclear reactions produce gamma rays. Some objects in space emit bursts of gamma rays. However, these rays are blocked by Earth's atmosphere. Astronomers think that explosions of distant stars produce these gamma rays.

X-rays

Electromagnetic waves with wavelengths just shorter than those of ultraviolet rays are X-rays. Their frequencies are just a little higher than ultraviolet rays. Because of their high frequencies, X-rays carry more energy than ultraviolet rays and can penetrate most matter. Dense matter, such as bone or lead, absorbs X-rays so they do not pass through. Therefore, X-rays are used to make images of bones and teeth. However, too much exposure to X-rays can cause cancer. X-rays can also be used in industry and engineering. Engineers can use an X-ray image of a steel or concrete structure to find cracks. Dark areas on the X-ray film show the cracks.

Ultraviolet rays

Electromagnetic waves with wavelengths just shorter than those of visible light are called ultraviolet rays. Ultraviolet rays have higher frequencies than visible light, so they carry more energy. The energy of ultraviolet rays can damage or kill living cells. For example, too much exposure to ultraviolet rays can burn your skin and over time may cause skin cancer. However, small doses of ultraviolet rays are useful. They cause skin cells to produce vitamin D, which is needed for healthy bones and teeth.