Light and Geometric Optics Flashcards
Unit E: Looking Ahead
Unit focuses on light and geometric optics.
Chapter 11: The Production and Reflection of Light.
Chapter 12: The Refraction of Light.
Chapter 13: Lenses and Optical Devices.
Unit Task: Building an Optical Device that satisfies a human need or want using the properties of light.
Consider social, health, environmental, and economic factors in designing and constructing the device.
Assessment will be based on planning and designing the device, building and improving the prototype, and explaining its function and societal usefulness.
What Do You Already Know? (Prerequisites)
Concepts: Light is a form of energy and travels in straight lines.
Skills: Drawing lines and measuring angles accurately, creating labeled diagrams, solving equations, using lab equipment safely, communicating scientific ideas, and writing lab reports.
Question 1: Main energy source for Earth is the Sun.
Question 2: Light shown in Figure 1 (unspecified type). Similarities and differences exist between this kind of light and the kind of light in your home.
Question 3: Shadow changes as your hand moves closer to or farther from the paper due to the straight path of light.
Question 4: Writing on a T-shirt appears reversed in a mirror. Similar to the writing on an ambulance (Figure 2).
Question 5: Funhouse mirrors are curved mirrors leading to a distorted view.
Question 6: Security mirrors are typically convex (Figure 3), making objects appear smaller, right side up, and backwards.
Question 7: A straw in a glass of water appears bent when viewed from above (Figure 4).
Chapter 11: The Production and Reflection of Light
Key Question: How do mirrors form images?
Key Concepts
Light is produced by natural and artificial sources.
Light travels as an electromagnetic wave at high speed in a straight line.
Images in flat mirrors are the same size as the object and the same distance from the surface.
Images in flat mirrors are located where backward extensions of reflected rays intersect.
Curved mirrors produce various types of images.
Engage in Science: The Laser
H. G. Wells's "The War of the Worlds" (1898) made an early fictional reference to lasers.
Lasers have many benign uses such as CD/DVD players, pointers, measuring devices, and scanning devices.
Lasers are used in manufacturing and entertainment.
Question: Why is the laser often portrayed as a dangerous weapon in mass media, and does mass media portray science realistically?
What Do You Think?
Series of statements about light, reflection, and related phenomena; readers are asked to agree or disagree with each statement.
Statement 1: Accuracy of a diagram showing light reflecting off water's surface.
Statement 2: Accuracy of a diagram depicting a laser beam reflecting off a curved mirror.
Statement 3: Whether a full-length mirror is necessary to see your whole body.
Statement 4: Accuracy of a diagram showing how an image appears in a makeup mirror.
Statement 5: Whether microwaves travel at the speed of light.
Statement 6: Whether a luminous object like a candle radiates light in all directions.
Focus on Writing: Writing a Persuasive Text
Purpose: Convince the audience to accept an opinion using strong reasons and logical thinking.
Example: Persuasive text arguing that LEDs are the best artificial lighting source.
Structure:
First paragraph introduces the topic and opinion.
Subsequent paragraphs state reasons to accept the opinion clearly.
Concluding paragraph connects ideas and reinforces the opinion.
Strategies:
Use clear opinion statements.
Support arguments with statistics and facts.
Use signal words to show relationships between ideas.
11.1 What Is Light?
Sunlight is the energy that makes life possible on Earth.
The Sun is approximately 1.50 \times 10^8 km from Earth.
Nuclear reactions in the Sun produce tremendous energy, including light, emitted in all directions.
Earth captures a tiny fraction of the Sun's light, providing energy to heat the surface and allow photosynthesis.
Plants are the basis of the food chain.
Light travels at a very high speed.
Light travels in straight lines.
A photon is a small packet of light energy.
Scientists once believed in a luminiferous ether as a medium for light travel, but now know light is an electromagnetic wave and needs no medium.
Heat energy can be transferred by conduction or convection, both of which require a medium.
Light energy is transferred through radiation.
In 1801, Thomas Young demonstrated light's wave-like properties.
In 1864, James Clerk Maxwell predicted the existence of electromagnetic waves that do not require a medium and travel at the speed of light.
In 1887, Heinrich Hertz discovered radio waves, confirming Maxwell's prediction.
In 1895, William Konrad Roentgen discovered X-rays.
The electromagnetic spectrum classifies electromagnetic waves by energy, including radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays, and gamma rays.
Visible light is the electromagnetic wave that the human eye can detect.
Electromagnetic waves have many modern uses.
White visible light is composed of a continuous sequence of colors called the visible spectrum: red, orange, yellow, green, blue, indigo, and violet.
A triangular prism slows down the speed of light, separating white light into different colors because each color travels at a different speed within the prism.
Isaac Newton was the first to separate white light into the visible spectrum in 1666.
Astronomers use different parts of the electromagnetic spectrum to study the universe, revealing more violent phenomena than visible light alone can show.
11.2 How Is Light Produced?
Light enters our eyes from all objects we see, either by radiating light (luminous) or reflecting light (non-luminous).
Luminous objects produce their own light (e.g., Sun, light bulb), while non-luminous objects reflect light (e.g., tree, textbook).
Incandescence is the production of light as a result of high temperature. As an object heats up, the emitted light changes from red to orange to yellow to white and then bluish-white.
Incandescent bulbs produce light by heating a thin wire filament, typically tungsten, until it glows. They are inefficient as they convert only 5-10% of electricity into visible light, with the rest becoming infrared light (heat).
Electric discharge is the process of producing light by passing an electric current through a gas. Different gases produce different colors of light (e.g., neon-red, helium-gold, argon-pale violet-blue, krypton-greyish off-white).
Geissler tubes, developed by Heinrich Geissler, were early forms of electric discharge lighting.
Phosphorescence is the process of producing light by the absorption of ultraviolet light, resulting in the emission of visible light over an extended period of time. Glow-in-the-dark materials use phosphors.
Fluorescence is the immediate emission of visible light as a result of the absorption of ultraviolet light. Fluorescent lights use both electric discharge and fluorescence, using mercury vapor to emit ultraviolet light, which then strikes a fluorescent coating to produce visible light. Fluorescent lights are more energy-efficient than incandescent bulbs.
Chemiluminescence is the production of light as a direct by-product of a chemical reaction with little or no heat produced, often called "cold light". Light sticks operate by mixing two chemicals.
Bioluminescence is chemiluminescence in living organisms (e.g., fireflies), often used for protection, luring prey, or attracting mates.
Triboluminescence is the production of light from friction, such as scratching, crushing, or rubbing certain crystals.
Light-emitting diodes (LEDs) produce light when an electric current flows in one direction through semiconductors. LEDs are energy-efficient and do not produce much heat.
11.3 The Laser - A Special Type of Light
Lasers emit electromagnetic radiation of a single energy level, producing pure color light.
Laser light is intense because the electromagnetic waves travel in the same direction and are in unison.
The Earth-Moon distance has been measured by scientists using lasers directed at the Moon with an accuracy of 3 cm.
11.4 The Ray Model of Light
Light travels in a straight line.
A light ray is a line and arrow representing the direction and straight-line path of light.
Geometric optics involves using light rays to determine the path of light when it strikes an object.
Incident light refers to the light emitted from a source that strikes an object.
Transparent objects allow light to pass through easily; translucent objects allow some light to pass through, and opaque objects do not allow any light to pass through.
An image is a reproduction of an object using light.
A mirror is any polished surface exhibiting reflection.
Reflection is the bouncing back of light from any surface.
A plane mirror, or flat mirror, illustrates how light behaves predictably.
The incident ray is the original incoming ray that strikes a surface.
The reflected ray is the ray that bounces off a reflective surface.
The normal is the line perpendicular to a mirror surface.
The angle of incidence is the angle between the incident ray and the normal.
The angle of reflection is the angle between the reflected ray and the normal.
11.5 Perform an Activity: Reflecting Light Off a Plane Mirror
Purpose is to compare the angle of incidence with the angle of reflection in a plane mirror.
Materials include a ray box, plane mirror, pencil, ruler, and protractor.
Procedure includes drawing a line on paper, placing a mirror on the line, aiming the ray at the mirror, drawing a normal, marking the paths of incident and reflected rays, and measuring angles.
11.6 The Laws of Reflection
When light is reflected off a plane mirror, the laws of reflection are:
The angle of incidence equals the angle of reflection.
The incident ray, the reflected ray, and the normal all lie in the same plane.
Specular reflection is the reflection of light off a smooth, shiny surface (e.g., plane mirror, still water).
Diffuse reflection is the reflection of light off an irregular or dull surface (e.g., paper, water with waves).
11.7 Images in Plane Mirrors
Virtual image is an image formed by light coming from an apparent light source; light is not physically arriving at the image location.
A plane mirror divides the object-image line in half and is perpendicular to that line.
When describing image properties, use the acronym SALT:
Size (same size, smaller, or larger)
Attitude (upright or inverted)
Location (where the image is located)
Type (real or virtual)
Image in a plane mirror is always the same size as the object, upright, behind the mirror, and virtual.