Life Science Chapter 2 Study Guide

Transcription

1 Key concepts and definitions Waves and the Electromagnetic Spectrum Wave Energy Medium Mechanical waves Amplitude Wavelength Frequency Speed Properties of Waves (pages 40-41) Trough Crest Hertz Electromagnetic wave Electromagnetic radiation Electromagnetic spectrum Key Concept: The basic properties of waves are amplitude, wavelength, frequency, and speed. In science, energy is defined as the ability to do work. A wave is a disturbance that transfers energy from place to place. The material through which a wave travels is called a medium. o Gases, liquids and solids can all be mediums Waves o Waves that require a medium through which to travel are called mechanical waves. o Mechanical waves are produces when a source of energy causes a medium to vibrate. o A vibration is a repeated back-and-forth or up-and-down motion. o All waves share certain properties. The basic properties of waves are amplitude, wavelength, frequency, and speed. Amplitude is how far the medium moves when a wave passes through it. Amplitude shows how much energy a wave has. Amplitude is the maximum distance the particles of the medium carrying the waves move away from the rest positions. The high point of the wave is called crest and the low point is a trough. Wavelength is how far a wave travels before it starts to repeat. To find the wavelength of a wave, you can measure the distance from crest to crest, or trough to trough. Frequency is the number of waves that go by a point in a certain amount of time. Frequency is measured in unit called hertz (Hz). If one wave passes a point each second, the frequency is 1Hz. The speed of a wave is how far it travels in a certain amount of time. What is an Electromagnetic Wave? (page42) Key Concept: An electromagnetic wave consists of vibrating electric and magnetic fields that move through space at the speed of light. 1 P a g e

2 An electromagnetic wave o is a wave that carries electrical and magnetic energy o The energy is called electromagnetic radiation. o Light is an example of an electromagnetic wave. o It does not need a medium through which to travel. They can travels through empty space. For example sunlight travels through empty space to reach Earth. o An electromagnetic wave consists of vibrating electric and magnetic fields that move through space at the speed of light. o Electromagnetic waves travel at the same speed. In empty space, they travel at about 300,000 km per second. This speed is called the speed of light. The energy that is transferred through space by electromagnetic waves is called electromagnetic radiation. What is the Electromagnetic Spectrum? (Pages 43-45) Key Concept: The electromagnetic spectrum is made up of radio waves, infrared rays, visible light, ultraviolet rays, X-rays, and gamma rays. The electromagnetic spectrum o Is the complete range of electromagnetic waves o The waves are placed in order of increasing frequency o The electromagnetic spectrum is made up of Radio waves Infrared rays Visible light Ultraviolet rays X-rays Gamma rays o Electromagnetic waves that you can see are called visible light. o As the frequencies of the wave get higher, the wavelengths get shorter o At one of the electromagnetic spectrum are radio waves. Radio waves have low frequencies and long wavelength. o At the other end of the spectrum are gamma rays. Gamma rays have high frequencies and short wavelengths. o The higher the frequency of electromagnetic waves, the more energy they have. Gamma rays have the highest frequency, so they have the most energy. 2 P a g e

3 Visible light and Color (Pages 46-50) Students should be able to 1. Describe how white light interacts with an object. 2. Describe what determines the color of an opaque object. 3. Explain how mixing pigments is different from mixing colors of light. Key Terms Transparent Translucent Opaque Primary colors Secondary colors Complementary colors Pigment 3 P a g e

4 Visible Light (page 47) Key Concept: When light strikes an object, the light can be reflected, transmitted, or absorbed. What happens to the light depends on the type of material the object is made of. Materials can be transparent, translucent, or opaque. It depends on what happens to the light that hits the material. Transparent materials let most light pass right through. You can see clearly through a transparent material. Clear glass is a transparent material. Translucent materials scatter light as it passes through. You can see things through a translucent material, but the details are blurred. Wax paper is a translucent material. Opaque materials do not let light pass through. They reflect or absorb all the light that hits them. When materials absorb light, they take in light. You cannot see anything through an opaque material. Wood is an opaque material. The Color of Objects (page 48) Key Concept: The color of an opaque object is the color of the light it reflects. The color of any object depends on what the object is made of and the color of light that hits it. Objects made of opaque materials reflect some light and absorb the rest. The color of the reflected light gives an opaque object its color. For example, an apple looks red because it reflects red light and absorbs light of other colors. Objects change color if you view them in a different color of light. In green light, an apple looks black. It looks black because there is no red light for it to reflect. Combining Colors (pages 49-50) Key Concept: When combined in equal amounts, the three primary colors of light produce white light. As pigments are added together, fewer colors of light are reflected and more are absorbed. Primary colors are three colors that can mix together to make any other color. Two primary colors mix in equal amounts to make a secondary color. Primary colors of light are red, green, and blue. Secondary colors of light are yellow (red and green), cyan (blue and green) and magenta (blue and red). Equal amounts of all three primary colors of light mix together to make white light. Any two colors that combine to form while light are called complementary colors. Pigments are colored material. They are used to color inks and paints. Pigments have different primary and secondary colors than light. Primary colors of pigments are yellow, cyan and magenta. Secondary colors of pigments are red (yellow and magenta), green (yellow and cyan) and blue (cyan and magenta). When equal amounts of all three primary pigment colors are mixed together, the mixture looks black. 4 P a g e

5 A wide range of colors can be produced using just a few basic colors. Three colors that can combine to make any other color are called primary colors. Two primary colors combine in equal amounts to produce a secondary color. The primary colors of light are red, green and blue. o The secondary colors of light are yellow (red + green), cyan (green + blue), and magenta (red + blue). When combined in equal amounts, the three primary colors of light produce white light. If the three primary colors of light are combined in different amounts, they can produce other colors. Complementary colors are a primary color and a secondary color that can combine to form white light. Blue and yellow are examples of complementary colors. Pigments are colored substances that are used to color other materials. o They include inks, paints, and dyes. o The color of a pigment is the color of light that the pigment reflects. o As pigments are added together, fewer colors of light are reflected and more are absorbed. o The more pigments that are combined, the darker the mixture looks. o The primary colors of pigments are cyan, yellow and magenta. o The secondary colors of pigments are red, green and blue. o The primary pigment colors combine in equal amounts to produce black. o Many other colors of pigments can be produced by combining the primary pigment colors in different amount. Primary Light Colors How we see color. 5 P a g e

6 All Visible light hits the red apple. 2. The red apple absorbs all light except red. It reflects red light. 3. The human eye receives the reflected red light. Sample Questions: 1. What happens to light that strikes a translucent material 2. The color of an opaque object is the color of the light it. 3. Explain why you see the skin of an apple as red. 4. The three colors that can be used to make any other color are called Key Terms Reflection Law of reflection Plane mirror Image Virtual image Concave mirror Optical axis Reflection and Refraction (pages 52-60) Focal point Real image Convex mirror Refraction Lens Convex Lens Concave Lens 6 P a g e

7 Objectives State the law of reflection. Explain why light rays bend as they enter a new medium at an angle. Explain what determines the types of images formed by convex and concave lenses. Reflection (Page 53) Key Concept: The law of reflection states that the angle of incidence equals the angle of reflection. When light waves hit a shiny surface, they bounce back. The bouncing back of light waves is called reflection. All waves obey the law of reflection. A wave that is moving toward a surface is the incoming wave. The wave that bounces off the surface is the reflected waves. The law of reflection states that the angle the incoming wave makes with the surface is equal to the angle the reflected wave makes with the surface. Mirrors (Pages 54-56) A plane mirror is a flat sheet of glass that has a smooth, silver-colored coating on the back. The coating reflects all the light that hits it. What you see when you look in a mirror is an image. o An image is a copy of an object. The image you see in a plane mirror is called virtual image. o A virtual image is an image that forms where the light seems to come from. The image looks as though it is behind the mirror. A virtual image is always right side up. 7 P a g e

8 Concave mirror A concave mirror is a mirror that curves inward like the inside of a bowl. A concave mirror reflects light rays toward the center of the mirror. The light rays all meet at the same point, called the focal point. o The focal point is on the optical axis, an imaginary line that divides a mirror in half. A concave mirror forms a virtual image if the object is between the mirror and the focal point. It forms a real image if the object is farther from the mirror than the focal point. o A real image forms when reflected light rays meet. o A real image is always upside down. Convex mirror A convex mirror is a mirror with a surface that curves outward like the outside of a bowl. Convex mirror reflects light rays outward. The reflected rays spread out and never meet. The image looks as though it is behind the mirror. 8 P a g e

9 Refraction (Pages 57-58) Key Concept: When light rays enter a medium at an angle, the change in speed causes the rays to bend or change direction. As light moves from one medium to the next, it bends. This bending is known as refraction. Light travels at different speeds in different mediums. For example, light travels more slowly in water than in air. Therefore, light slows down when it passes from air into water. When a light wave passes from air into water at an angle, one side of the light wave slows down before the other side. This causes the light to bend, or refract. When light rays enter a medium at an angle, the change in speed causes the rays to bed, or change direction. 9 P a g e

10 Lenses (Pages 58-60) Life Science Chapter 2 Study Guide Key Concept: An object s position relative to the focal point determines whether a convex lens forms a real image or a virtual image. A concave lens can produce only virtual images because parallel light rays passing through the lens never meet. A lens is curved piece of glass that is used to bend light. The type of image formed by a lens depends on the shape of the lens and the position of the object. A convex lens is thicker in the center than at the edges. A convex lens bends light rays toward the center of the lens. All the rays pass through the focal point. An object s position relative to the focal point determines whether a convex lens forms a real image or a virtual image. A concave lens is thinner in the center than at the edges. A concave lens bends light away from the center of the lens. The light rays never meet, so the image is always a virtual image. The image is upright and smaller than the object. A concave lens can produce only virtual images because parallel light rays passing through the lens never meet. 10 P a g e

11 Seeing Light Vision (page 63) Concepts and definitions: Cornea Pupil Iris Retina Chapter 2 section 4 Rods Cones Nearsighted Farsighted Key Concepts: When light from an object enters your eye, your eye sends a signal to your brain and you see the object. Your eyes let you sense light. Your eyes have many parts. o Cornea: The cornea is a clear white covering over the outside of the eye. It helps the eye focus like a lens on a camera. o The pupil is the part of the eye that looks black. It lets light pass into the eye o The iris is the colored part of the eye. It controls the size of the pupil and how much light enters the eye. o The lens is convex. It bends the light to form an image. o Lens: The lens bends light. This helps the eye see close up and far away things. o The image forms on the retina. o The retina is the inside lining at the back of the eye. The retinal sends signals about the image to your brain. o The retina is made up of tiny, light-sensitive cells called rods and cones. o Rods respond to smaller amounts of light. Cones respond to color. o Optic Nerve: The optic nerve carries electrical signals from your retina to your brain so you can see. 11 P a g e

12 VISION Your eyes allow you to sense light. When light from an object enters your eye, your eye sends a signal to your brain and you see the object. a) Light enters the eye through the transparent front surface called the cornea. b) Then light enters the pupil, the part of the eye that looks black. i) The pupil is an opening through which light enters the inside of the eye. ii) In dim light, the pupil becomes larger to allow in more light. iii) In bright light, the pupil becomes smaller to allow in less light. c) The iris is a ring of muscle that contracts and expands to change the size of the pupil. d) After entering the pupil, light passes through the lens. e) The lens bends light to form an upside-down image on the retina. i) The retina is a layer of cells that line the inside of the eyeball. ii) The retina is made up of tiny light-sensitive cells called rods and cones. (1) Rods contain a pigment that responds to small amounts of light. (2) Cones respond to color. They made 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 along the optic nerve. 12 P a g e

13 Key Concepts: Concave lenses are used to correct nearsightedness. Convex lenses are used to correct farsightedness. How do you see objects? What types of lenses are used to correct vision problems? When an eyeball is too short or too long, images do not form on the retina. This makes the images look blurred. Lenses in glasses or contacts can correct the problem. Lenses focus the images on the retina. A nearsighted person can see nearby objects clearly, but distant blurred. They eyeball is too long. Images focus in front of the retina. Concave lenses can correct this type of vision problem. A farsighted person can see distant objects clearly, but nearby objects looked blurred. The eyeball is too short. Images focus behind the retina. Convex lenses can correct this type of vision problem. If the eyeball is slightly too long or too short, the image on the retina is out of focus. o Wearing glasses or contact lenses can correct this type of vision problem. o Concave lenses are used to correct nearsightedness. o Convex lenses are used to correct farsightedness. A nearsighted person can see nearby objects clearly, but distant objects are blurred. The eyeball is too long, so the image forms in front of the retina. A farsighted person can see distant objects clearly, but nearby objects are blurred. The eyeball is too short, so the image that falls on the retina is out of focus. 13 P a g e

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15 Concepts and definitions: Camera Telescope Refracting telescope Objective Optical Tools (pages 65-69) Eyepiece Reflecting telescope Microscope Electron microscope Cameras (page 66) Key Concept: The lens of the camera focuses light to form a real, upside-down image on film in the back of the camera. 1. A camera uses one or more lenses to focus light. It uses film to record an image. The lens forms an image on the film. 2. Light from an object passes through the lens of a camera. The light rays bend as they pass through the lens. 3. The lens moves closer to or away from the film until the image is focused. Telescopes (page 67) Key Concept: Telescopes uses combinations of lenses or mirrors to collect and focus light from distant objects. Objects that are far away are hard to see. The light from distant objects has spread out by the time it reaches your eye. A telescope makes a large image of objects that are far away. It collects light from distant objects, then focuses it to make a large image. A refracting telescope has two convex lenses. one lens is at each end of the tube. The larger the lens is called the objective. It gathers the light from the object. It focuses the rays of light from the object and forms a real image. The lens closest to your eye is called the eyepiece. The eyepiece makes the image larger so you can see it. The image you see is upside down. A reflecting telescope uses a large concave mirror. A concave mirror gathers light from the object and focuses the light to form a real image. A small mirror inside the telescope reflects the image to the eyepiece. The image you see is upside down. 15 P a g e

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17 Microscopes (pages 68-69) Life Science Chapter 2 Study Guide Key Concept: A microscope uses a combination of lenses to form enlarged images of tiny objects. A microscope makes large images of small objects look larger. It is important that microscopes make large images that are sharp and clear. Two types of microscope: 1. Light microscope 2. Electron microscope A light microscope uses convex lenses to make objects look larger. Remember that when light rays pass a convex lens, they come together at a point. When these light rays meet and hit the eye, the eye sees the object as larger than it really is. A light microscope uses more than one lens. The first lens is called the objective. It makes the image larger. The second lens is called the eyepiece. It makes the large image even larger. 17 P a g e

18 An electron microscope uses a beam of electrons instead of light. Electrons are smaller than atoms. Electron microscopes can make pictures of very tiny objects. The images they create are much sharper and clearer than images from light microscopes. 18 P a g e

19 Three common types of optical instruments are telescopes, microscopes, and cameras. A camera uses one or more lenses to focus light. It records images on film. Light from an object travels to the camera and passes through the lens. The lens of the camera focuses light to form a real, upside-down image on film in the back of the camera. A telescope forms enlarged images of distant objects. Telescopes use combinations of lenses or mirrors to collect and focus light from distant objects. The most common uses of telescope is to study objects in space. Two main types of telescopes are refracting telescopes and reflecting telescopes. A refracting telescope consists of two convex lenses, one at each end of a long tube. The larger lens is called the objective. The objective gathers the light coming from an object. It focuses the rays to form a real image. The lens close to your eye is called the eyepiece. The eyepiece magnifies the image so you can see it clearly. A reflecting telescope uses a large concave mirror to gather light. The mirror collects light from distant objects and focuses the rays to form a real image. A small mirror inside the telescope reflects the image to the eyepiece. The images you see through the telescope are upside down. 19 P a g e

20 A microscope is an optical tool that makes small objects look larger. A microscope uses a combination of lenses to form enlarged images of tiny objects. For microscope to be useful, it must combine two important properties- magnification and resolution. The lenses in light microscopes magnify an object by bending the light that passes through them. Since light microscopes have more than one lens, they are also called compound microscopes Light passes through a specimen and then through two lenses. The first lens, the objective magnifies the object. Then a second lens, the eyepiece, further magnifies the enlarged image. The total magnification of the microscope is equal to the magnifications of the two lenses multiplied together. The electron microscope uses a beam of electrons instead of light to produce a magnified image. Electron microscopes can obtain pictures of extremely small objects- much smaller than those that can be seen with light microscopes. The resolution of electron microscopes is much better than the resolution of light microscopes. 20 P a g e