# Relationship between incidence and reflection angles on a mirror

### Angle of Incidence, Angle of Incidence and Reflection | [email protected]

The law of reflection states that the incident ray, the reflected ray, and the normal to the surface of the mirror all lie in the same plane. Furthermore, the angle of. Learn about the properties of light waves and how they can be reflected, refracted and drawn at 90° to the surface of the mirror; the angle of incidence. Reflected light obeys the law of reflection, that the angle of reflection equals the angle of incidence. In a ray diagram, rays of light are drawn from the object to the mirror, . The magnification, m, is defined as the ratio of the image height to the object height, which is closely related to the ratio of the image.

The angles of incidence and reflection are measured from a normal to the plane of the mirror as shown in Figure 1.

• The Law of Reflection
• All Things Equal
• Angle of Incidence

Reflection from a Diffuse Surface Figure 2. Some surfaces seem quite smooth; for example, a sheet of paper. However, we do see any reflections as with a plane-mirror.

## Light waves

At the microscopic scale the law of reflection is obeyed but the surface is irregular which means the incident rays of light are reflected in many directions and the information contained in the in the light does not reach the eye in the correct order.

This is known as diffuse reflection Rotation of Plane-Mirror Figure 3. Sign conventions What does a positive or negative image height or image distance mean? To figure out what the signs mean, take the side of the mirror where the object is to be the positive side.

Any distances measured on that side are positive. Distances measured on the other side are negative. When the image distance is positive, the image is on the same side of the mirror as the object, and it is real and inverted. When the image distance is negative, the image is behind the mirror, so the image is virtual and upright. A negative m means that the image is inverted.

Positive means an upright image. Steps for analyzing mirror problems There are basically three steps to follow to analyze any mirror problem, which generally means determining where the image of an object is located, and determining what kind of image it is real or virtual, upright or inverted.

Step 1 - Draw a ray diagram. The more careful you are in constructing this, the better idea you'll have of where the image is. Step 2 - Apply the mirror equation to determine the image distance. Or to find the object distance, or the focal length, depending on what is given.

Step 3 - Make sure steps 1 and 2 are consistent with each other. An example A Star Wars action figure, 8. Where is the image? How tall is the image? What are the characteristics of the image? The first step is to draw the ray diagram, which should tell you that the image is real, inverted, smaller than the object, and between the focal point and the center of curvature.

The location of the image can be found from the mirror equation: The image distance is positive, meaning that it is on the same side of the mirror as the object. This agrees with the ray diagram. Note that we don't need to worry about converting distances to meters; just make sure everything has the same units, and whatever unit goes into the equation is what comes out.

Intro to Reflections from Concave Mirrors - Geometric Optics - Doc Physics

Calculating the magnification gives: Solving for the image height gives: The negative sign for the magnification, and the image height, tells us that the image is inverted compared to the object. To summarize, the image is real, inverted, 6. Example 2 - a convex mirror The same Star Wars action figure, 8. Where is the image in this case, and what are the image characteristics? Again, the first step is to draw a ray diagram.

This should tell you that the image is located behind the mirror; that it is an upright, virtual image; that it is a little smaller than the object; and that the image is between the mirror and the focal point. The second step is to confirm all those observations.

The mirror equation, rearranged as in the first example, gives: Solving for the magnification gives: This gives an image height of 0. All of these results are consistent with the conclusions drawn from the ray diagram. The image is 5. Refraction When we talk about the speed of light, we're usually talking about the speed of light in a vacuum, which is 3.

When light travels through something else, such as glass, diamond, or plastic, it travels at a different speed. Diffuse Reflection Light is known to behave in a very predictable manner. If a ray of light could be observed approaching and reflecting off of a flat mirror, then the behavior of the light as it reflects would follow a predictable law known as the law of reflection.

The diagram below illustrates the law of reflection. In the diagram, the ray of light approaching the mirror is known as the incident ray labeled I in the diagram.

The ray of light that leaves the mirror is known as the reflected ray labeled R in the diagram. At the point of incidence where the ray strikes the mirror, a line can be drawn perpendicular to the surface of the mirror. This line is known as a normal line labeled N in the diagram. The normal line divides the angle between the incident ray and the reflected ray into two equal angles. The angle between the incident ray and the normal is known as the angle of incidence.

The angle between the reflected ray and the normal is known as the angle of reflection. These two angles are labeled with the Greek letter "theta" accompanied by a subscript; read as "theta-i" for angle of incidence and "theta-r" for angle of reflection.

### Relfection from a Plane Mirror

The law of reflection states that when a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflection.

Reflection and the Locating of Images It is common to observe this law at work in a Physics lab such as the one described in the previous part of Lesson 1. To view an image of a pencil in a mirror, you must sight along a line at the image location.

As you sight at the image, light travels to your eye along the path shown in the diagram below. The diagram shows that the light reflects off the mirror in such a manner that the angle of incidence is equal to the angle of reflection.