Thursday, July 28, 2011
Thursday, July 21, 2011
The Spherical Mirror Equation
The position and size of the image formed by curved mirrors may be determined graphically using Ray Diagrams. However, these can be determine more quickly by analytical methods by using the Spherical Mirror Equation
Since the image distance is often the quantity to be found, a convenient alternative form of this equation is
Magnification Equation for a Spherical Mirror
Since the image distance is often the quantity to be found, a convenient alternative form of this equation is
Magnification Equation for a Spherical Mirror
Ray Diagram
Pratice how to construct a Ray Diagram. Study the illustraions. Draw the three major rays (Parallel Ray, Chief Ray or Radial Ray and Focal Ray)
Parallel Ray - A ray that travels parallel to the optic axis and is reflected through the focal point.
Chief Ray or Radial Ray - A ray that travels through the center of the sphere and is reflected back along the path it came.
Focal Ray - A ray that travels through the focal point and is mirrored parallel to the optic axis.
Parallel Ray - A ray that travels parallel to the optic axis and is reflected through the focal point.
Chief Ray or Radial Ray - A ray that travels through the center of the sphere and is reflected back along the path it came.
Focal Ray - A ray that travels through the focal point and is mirrored parallel to the optic axis.
Curved Mirrors
Not all mirrors are flat. There are also curved or spherical mirrors. These mirrors reflect light in special ways.
Let's imagine a ball. Concave mirrors are the ones whose reflecting surface is the inside part of the ball. Convex mirrors are the ones whose reflecting surface is the outside part of the ball.
Now, let's imagine the center of the ball. This is called the center of curvature (C). The line that passes through the center of curvature and the mirror is the principal axis and the midpoint between the center of curvature and the mirror on the principal axis is called the principal focus (F).
In a concave mirror, the reflected ray will pass through the principal focus if the incident ray is parallel to the principal axis. In a convex mirror, the reflected ray will seem to come from the principal focus if the incident ray is parallel to the principal axis.
The image formed by a convex mirror is also virtual, upright, smaller than the object and is always located behind the mirror. While the type of image formed by a concave mirror depends on the location of the object in front of the concave mirror.
Concave mirrors are converging mirrors while convex mirrors are diverging mirrors.
Let's imagine a ball. Concave mirrors are the ones whose reflecting surface is the inside part of the ball. Convex mirrors are the ones whose reflecting surface is the outside part of the ball.
Now, let's imagine the center of the ball. This is called the center of curvature (C). The line that passes through the center of curvature and the mirror is the principal axis and the midpoint between the center of curvature and the mirror on the principal axis is called the principal focus (F).
In a concave mirror, the reflected ray will pass through the principal focus if the incident ray is parallel to the principal axis. In a convex mirror, the reflected ray will seem to come from the principal focus if the incident ray is parallel to the principal axis.
The image formed by a convex mirror is also virtual, upright, smaller than the object and is always located behind the mirror. While the type of image formed by a concave mirror depends on the location of the object in front of the concave mirror.
Concave mirrors are converging mirrors while convex mirrors are diverging mirrors.
On Plane Mirror
Key Thoughts About Plane Mirror
A mirror with a flat surface is called PLANE MIRROR. The image formed by a plane mirror appears to be "behind or inside the mirror". The type of image is called a virtual image. A virtual image is oriented upright but is laterally inverted. Lateral inversion means that when you look at a plane mirror your right side seems to be your left side and your left side seems to be your right side. This concept explains why the letters of the word AMBULANCE are printed backwards and are reversed in sequence.
The image formed by a plane mirror appears to be at a distance behind the mirror that is equal to the distance of the object in front of the mirror. In other words, the distance of the object is the same as the distance of the image. The size of the image is also the same as the size of the object. The lateral magnification is equal to one M = 1 meaning there is no magnification.
The illustration below is similar to our first hands-on activity on reflection of light
If you will analyze the illustration, the distance of the object (pin) is the same as the distance of the image. Likewise, the size of the object is the same as the size of the image. We will see that the angle of incidence is equal to the angle of reflection.
A mirror with a flat surface is called PLANE MIRROR. The image formed by a plane mirror appears to be "behind or inside the mirror". The type of image is called a virtual image. A virtual image is oriented upright but is laterally inverted. Lateral inversion means that when you look at a plane mirror your right side seems to be your left side and your left side seems to be your right side. This concept explains why the letters of the word AMBULANCE are printed backwards and are reversed in sequence.
The image formed by a plane mirror appears to be at a distance behind the mirror that is equal to the distance of the object in front of the mirror. In other words, the distance of the object is the same as the distance of the image. The size of the image is also the same as the size of the object. The lateral magnification is equal to one M = 1 meaning there is no magnification.
The illustration below is similar to our first hands-on activity on reflection of light
If you will analyze the illustration, the distance of the object (pin) is the same as the distance of the image. Likewise, the size of the object is the same as the size of the image. We will see that the angle of incidence is equal to the angle of reflection.
Sunday, July 17, 2011
Using the Law of Reflection to Measure Heights
Our Outdoor Physics Activity on Law of Reflection
We can apply the law of reflection and some concepts in geometry to measure the height of an object that would be very difficult to measure directly.
I hope you enjoy doing this activity.
In the diagram below, "h" is the height of the person's eyes above the surface of the water, and "d" is the horizontal distance from the person to the center of the bowl. "H" represents the height of the flagpole, and "D" is the horizontal distance from the flagpole to the bowl of water. The 3 distances h, d, and D are easy to measure.
Congratulations to the groups that got the closest to the actual height of the pole. More exciting activities to come...
We can apply the law of reflection and some concepts in geometry to measure the height of an object that would be very difficult to measure directly.
I hope you enjoy doing this activity.
In the diagram below, "h" is the height of the person's eyes above the surface of the water, and "d" is the horizontal distance from the person to the center of the bowl. "H" represents the height of the flagpole, and "D" is the horizontal distance from the flagpole to the bowl of water. The 3 distances h, d, and D are easy to measure.
Congratulations to the groups that got the closest to the actual height of the pole. More exciting activities to come...
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