Key Concept 1: Light Travels in Straight Lines Until Reflected Or Refracted by Another Object

5.6C- Light

Explanation:

Understanding how light energy travels and can be reflected or refracted are essential concepts in physical science.

Key Concept 1: Light travels in straight lines until reflected or refracted by another object.

Visible light energy, which the human eye is able to detect, referred to in this concept, represents only a narrow sliver of the electromagnetic spectrum.

This light is often produced when something becomes very hot. The Sun is our biggest and most important source of light. With a surface temperature of about 5500°C, the Sun produces vast amounts of visible and invisible light. An electric light bulb gives off light when electricity heats up a filament to about 2200°C, causing it to glow.

Light rays from any light source travel outward in all directions along a straight path–until they hit something. Then, light rays can reflect (bounce), refract (bend), be absorbed, or can pass straight through the material. Even though light can be absorbed by opaque objects and transmitted through clear objects, only reflection and refraction of light energy are the focus in the fifth grade.

Key Concept 2: Light is reflected when it bounces off of mirrors or shiny surfaces.

The image we see in a reflection is a flipped image from the original. Because light travels in straight lines, the angle of incoming light equals the angle of the reflected outgoing light on shiny surfaces. On dull surfaces, light rays reflect in many directions, called “scattered” light. The color the eye detects depends on which wavelengths of light are absorbed and reflected. If dull objects scatter all wavelengths, they appear white. If they absorb all wavelengths, they appear black. If dull objects absorb all wavelengths but reflect red, the eye detects red objects. When a surface is very smooth, like polished metal, glass, or the surface of still water, light is reflected like a mirror.

Interesting results occur when the surface of a shiny object is curved. If the reflective surface is convex (curves away from the incoming light), the light rays bounce off and spread out (diverge), like looking at the backside of a spoon. The image in a convex mirror appears to be smaller, upright, and covers a wider field of view. Security mirrors on the sides of halls or building walls, and side mirrors on trucks and cars, take advantage of the wide field of view created from a convex mirror reflection. If the reflective surface is concave (curves toward the incoming light), the light rays bounce off and come to a point (converge), like looking at the bowl of a spoon. The image is reversed but larger. Telescopes, a dentist’s mirror tool, and cosmetic mirrors take advantage of the magnified image created from a concave mirror reflection.

Key Concept 3: Light is refracted, or bends, when passing from one medium to another, such as from air into water.

A refracted image is distorted or a changed from the original. When light rays are transmitted or pass from one medium to another (from air to water) other than straight on, the speed of light changes slightly, which causes the light rays to change direction slightly at the boundary of those two mediums. This bending of light rays is called refraction. This happens when you look at a pencil in water, and the part below the surface of the water looks bent. This refraction of light can cause partially submerged objects in water to appear distorted.

Refracting light is important to the eye. The amazing flexible convex lens inside the eye focuses incoming light that our brain interprets as the world humans see. For those with poor vision, eyeglass lenses can refract or bend light rays to focus better or to magnify the image. Convex lenses (curved away from incoming light) are also used to make objects appear closer. Hand lenses, microscopes, telescopes, or binoculars are examples of convex lenses. Concave lenses (curved toward incoming light) are used to spread out images. Concave lenses are used in glasses to correct nearsightedness (myopia), and in door viewers, or peepholes.

Remind students that light rays can also pass straight through to the other side without refracting or bending the light, such as light passing through glass windows.

5.6B- Circuits and Electricity

Explanation:

Understanding the difference between open and closed electrical circuits, and how electrical energy can be changed into light, heat, and sound energy are essential concepts in physical science. In fourth grade, students differentiated between conductors and insulators. Students also demonstrated that electricity travels in a closed path, creating an electrical circuit, and explore an electromagnetic field.

Key Concept 1: Electricity flows in a closed path to form a circuit, and stops when the circuit is broken.

Electricity is a form of energy produced when electrons move along a path called a circuit. An atom has a nucleus containing protons and neutrons. Surrounding the nucleus is a cloud of electrons. Metals, such as copper, have loosely attached electrons in their outer orbits. These electrons roam randomly around the other copper atoms. When these free electrons are charged and move between the atoms, a current of electricity is created.

Electricity is conducted better through some materials than others. Conductors are materials with loosely held electrons that allow electrons to flow, such as copper, aluminum, and steel. Insulators are materials that hold their electrons very tightly and do not allow electrons to flow. Examples of insulators are rubber, plastic, glass, wood, and cloth.

A completed path or closed circuit can conduct electricity, while an incomplete path or open circuit will prevent electricity from flowing. In a closed circuit, a switch is flipped on and a piece of metal closes the pathway so that electrical current flows. In an open circuit, a switch is flipped off, which makes the path incomplete, and the electricity ceases to flow. A battery or a generator produces the pressure or force (measured in volts) that pushes the current through these wires. Circuits can be large or quite small. Some circuits involve huge power plants that generate electricity at one end and send megawatts of electricity along power lines to homes or business hundreds of miles away at the other end. Other circuits can be incredibly small, such as those in electronics that send information using tiny microchips.

Key Concept 2: We can demonstrate that electricity can produce light, heat, and sound when flowing through a circuit.

Students can use wire, batteries, and a switch to construct a simple circuit attached to a light bulb to show that electricity produces light and heat energy. When electricity flows to a light bulb, the filament inside becomes hot and glows. They can substitute a buzzer in place of the light bulb in the electrical circuit to produce vibrations, which produce sound energy. When an electric current flows to a TV, both sound and light are produced. When electric current flows to a toaster, the heating element wires get hot enough to turn bread a toasty brown.

Key Concept 3: Many everyday devices use electricity to produce light, heat, and sound.

Some devices use electrical energy for only one purpose. Examples of light-producing devices are light bulbs, flashlights, and neon signs. When an electric current flows to a toaster, the heating element wires get hot enough to turn bread a toasty brown. Heating elements in irons and clothes dryers work the same way. Radios, microphones, and loud speakers produce sound energy. However, many electrical devices produce a combination of energy outputs: televisions, computers, washing machines, automobiles, etc.

5.6A- Uses of Energy

Explanation:

Understanding energy and its uses is a key concept in physical science, life science, and earth science. In third grade, students learned that forces cause change and that energy exists in many forms. Subsequent lesson on electric circuits and on reflection and refraction of light provide more depth on electrical and light energy.

Key Concept 1: There are different types of energy, including mechanical, light, thermal, electrical, and sound energy: Energy is the ability to do work.

From the enormous amounts of energy necessary to lift a rocket, to the tiny amount of energy needed to lift an apple 1 meter, there is a constant interchange between matter and energy, big and small. A small amount of mass can be converted into a huge amount of energy. Converting matter to energy can be as simple as burning a match or as complex as the Sun converting matter into heat and light energy that illuminates our Solar System. The total amount of energy in the Universe remains constant; energy just keeps changing form.

Note:

Power is often incorrectly used as a synonym for energy. Energy is the ability to do work. Power is the rate at which energy is used or work is done. So power is a measurement of energy used per second (as in watts, for example). The amount of energy needed to do work can vary greatly.

Mechanical energy is the energy possessed by an object due to its motion or position. Mechanical energy can be in the form of kinetic or potential energy. Kinetic energy is the energy that comes from movement, and potential energy is the stored energy that comes from an object’s placement. A ball flying through the air has kinetic (movement) energy due to its mass and the speed of its movement. A tightly wound spring in a windup toy is ready to move, so it has potential (stored) energy, which will change to kinetic energy (movement) when the spring is released. The string of a bow when drawn back to shoot an arrow has mechanical (potential) energy, and, when released, changes to kinetic energy to rapidly push the arrow away from the bow. Every time anything moves, whether it’s the wind, water, cars, trees, people, clocks, or animals, energy makes it happen. All movement is mechanical energy.

Thermal or heat energy is felt coming from a fire, a hot cup of coffee, or a heating stove. Temperature is a measure of how much thermal energy an object has. The higher the temperature the faster the particles, or molecules, of an object are moving. A cooking stove heats the air inside an oven, and when cake batter is placed in the oven, the thermal heat of the air is transferred to the batter resulting in a baked cake. A microwave works differently; it uses microwaves (radiant energy with long wavelengths) to make the particles inside microwaved food move rapidly. The faster-moving particles generate heat and cook the food.

Light energy is part of the electromagnetic spectrum of radiant energy that our eyes can see. Stars, such as our Sun, produce their own light energy and shine brilliantly. Light bulbs and matches give off light energy. Light is able to travel through space, unlike sound that requires air or some other medium to be transmitted. Light energy travels in a straight line, but can be reflected. Light is reflected when it bounces off a shiny surface, such as a mirror. Light can also be refracted, meaning its rays can be “bent” when traveling from one medium to another. Because light travels slower in water than in air, a pencil placed in a cup of water will appear broken at the point of entry into the water. Curved lenses in telescopes or in eyeglasses refract light in order to magnify an image. Advances have been made recently to utilize light energy beyond just illumination. Laser lights have become important tools for doctors in surgery, for the manufacture of CD and DVD players and computers, and even for teachers and speakers who use laser pointers in their presentations.

Electrical energy is created when electrons, or small particles of atoms, move along a path called a circuit. For the electrons to flow, the circuit of wires must be closed, that is to say the path along which electrons are flowing must not be broken or open anywhere along the way. When an electric light is turned on, an electrical circuit is closed, giving power to the light. When a switch is flipped off, the circuit is opened and the electricity ceases to flow. Materials that allow electrons to flow easily, such as copper wire, are called conductors. Materials such as rubber or plastic, are called insulators. When electricity passes through coils of wire, it can create an electromagnetic field. All electric motors, in everything from toy cars to powerful fans, use electromagnetic fields to generate power.

Sound energy is created when an object vibrates and sends these vibrations through air. When we hear someone speak, it is because of the effects of sound energy. The vibrations of the speaker’s vocal chords pushes the air molecules around them, which travel as sound waves to the listener’s ear. Our ears are designed to be sensitive to these waves of sound, which our nerves and brain translates into the voice we hear. Striking a metal rod and feeling the vibration of the ringing rod, or simply placing our hand on our throat and speaking can demonstrate sound waves. Sound energy requires a medium, such as air or water to transmit, which is why sound does not travel in space.

Key Concept 2: We can use different types of energy, including mechanical, light, thermal, electrical, and sound energy.

Energy can be observed in our natural and human-made world. Sunlight, rushing rivers, hot summer days, lightning, and the sound of thunder are examples of energy in our natural world. Humans have learned how to harness that energy. Inventions take advantage of cycles and patterns that work in and out of energy systems. Air and fuel are inputs in an engine system; exhaust, heat, and mechanical work are outputs. Sound energy and electrical energy are inputs in a telephone system; sound energy and heat energy are outputs. In other words, humans have learned that energy is neither created nor destroyed, but can be transferred from one form to another to make work easier and life more enjoyable.

Key Concept 3: Bicycles, stereos, computers, lamps, and toasters are useful objects that demonstrate the use of mechanical, sound, electrical, light, and thermal energy.

Energy is essential for living: It takes energy to cook a meal, ride a bicycle, speak to a friend, turn on a computer, or listen to a song. We use energy every day. From the first simple wheel invented by ancient civilizations to roll a cart using mechanical energy, to the complexity of modern machines that convert electrical energy into countless applications, humans continue to make profound changes to the world using energy.