# How to draw ray diagrams

By | 11.02.2021

One theme of the Reflection and Refraction units of The Physics Classroom Tutorial has been that we see an object because light from the object travels to our eyes as we sight along a line at the object.

Similarly, we see an image of an object because light from the object reflects off a mirror or refracts through a transparent material and travel to our eyes as we sight at the image location of the object. From these two basic premises, we have defined the image location as the location in space where light appears to diverge from. Because light emanating from the object converges or appears to diverge from this location, a replica or likeness of the object is created at this location.

For both reflection and refraction scenarios, ray diagrams have been a valuable tool for determining the path of light from the object to our eyes. In this section of Lesson 5, we will investigate the method for drawing ray diagrams for objects placed at various locations in front of a double convex lens.

To draw these ray diagrams, we will have to recall the three rules of refraction for a double convex lens:. Earlier in this lesson, the following diagram illustrating the path of light from an object through a lens to an eye placed at various locations was shown. In this diagram, five incident rays are drawn along with their corresponding refracted rays.

Each ray intersects at the image location and then travels to the eye of an observer. Every observer would observe the same image location and every light ray would follow the Snell's Law of refraction. Yet only two of these rays would be needed to determine the image location since it only requires two rays to find the intersection point. Of the five incident rays drawn, three of them correspond to the incident rays described by our three rules of refraction for converging lenses.

We will use these three rays through the remainder of this lesson, merely because they are the easiest rays to draw. Certainly two rays would be all that is necessary; yet the third ray will provide a check of the accuracy of our process.

The method of drawing ray diagrams for double convex lens is described below. The description is applied to the task of drawing a ray diagram for an object located beyond the 2F point of a double convex lens.

Pick a point on the top of the object and draw three incident rays traveling towards the lens. Once these incident rays strike the lens, refract them according to the three rules of refraction for converging lenses.

Mark the image of the top of the object. Repeat the process for the bottom of the object. Some students have difficulty understanding how the entire image of an object can be deduced once a single point on the image has been determined.

If the object is merely a vertical object such as the arrow object used in the example belowthen the process is easy. The image is merely a vertical line. In theory, it would be necessary to pick each point on the object and draw a separate ray diagram to determine the location of the image of that point.

That would require a lot of ray diagrams as illustrated in the diagram below. Fortunately, a shortcut exists. If the object is a vertical line, then the image is also a vertical line. For our purposes, we will only deal with the simpler situations in which the object is a vertical line that has its bottom located upon the principal axis.

For such simplified situations, the image is a vertical line with the lower extremity located upon the principal axis. The ray diagram above illustrates that when the object is located at a position beyond the 2F point, the image will be located at a position between the 2F point and the focal point on the opposite side of the lens. Furthermore, the image will be inverted, reduced in size smaller than the objectand real. This is the type of information that we wish to obtain from a ray diagram.

These characteristics of the image will be discussed in more detail in the next section of Lesson 5.The images formed by a lens can be:. A real image is an image that can be projected onto a screen. A virtual image appears to come from behind the lens.

The type of image formed by a convex lens depends on the lens used and the distance from the object to the lens. Cameras and eyes contain convex lenses. For a distant object that is placed more than twice the focal length from the lens, the image is:. Projectors contain convex lenses. For an object placed between one and two focal lengths from the lens, the image is:. In a film or data projector, this image is formed on a screen. Film must be loaded into the projector upside down so the projected image is the right way up.

A magnifying glass is a convex lens used to make an object appear much larger than it actually is. This works when the object is placed at a distance less than the focal length from the lens. The image is:. Only the person using the magnifying glass can see the image. The image cannot be projected onto a screen because it is a virtual image. Concave lenses always produce images that are:. Peep holes are set into doors so the occupant can identify a visitor before opening the door. For an object viewed through a concave lens, light rays from the top of the object will be refracted and will diverge on the other side of the lens.

These rays will appear:. Real and virtual images The images formed by a lens can be: upright or inverted upside down compared to the object magnified or diminished smaller than the object real or virtual A real image is an image that can be projected onto a screen.

Convex lenses The type of image formed by a convex lens depends on the lens used and the distance from the object to the lens.

A camera or human eye Cameras and eyes contain convex lenses. For a distant object that is placed more than twice the focal length from the lens, the image is: inverted upside down diminished smaller than the object real can be produced on a screen Ray diagram for an object placed more than two focal lengths away from a convex lens Projectors Projectors contain convex lenses.

For an object placed between one and two focal lengths from the lens, the image is: inverted upside down magnified larger than the object real can be produced on a screen Ray diagram for an object placed between 2F and F from a convex lens In a film or data projector, this image is formed on a screen.

Magnifying glasses A magnifying glass is a convex lens used to make an object appear much larger than it actually is. The image is: upright the right way up magnified larger than the object virtual cannot be produced on a screen Ray diagram for an object placed less than one focal length from a convex lens Only the person using the magnifying glass can see the image.

Concave lenses Concave lenses always produce images that are: upright diminished virtual Peep hole lenses Peep holes are set into doors so the occupant can identify a visitor before opening the door.

Ray diagram for an object viewed through a concave lens For an object viewed through a concave lens, light rays from the top of the object will be refracted and will diverge on the other side of the lens. These rays will appear: from the same side of the principal axis meaning the image will be upright further from the principal axis, so the image will be larger than the object.The images formed by a lens can be:.

A real image is an image that can be projected onto a screen.

### Ray Diagrams

A virtual image appears to come from behind the lens. To draw a ray diagram :. Some ray diagrams may also show a third ray. The type of image formed by a convex lens depends on the lens used and the distance from the object to the lens.

Cameras and eyes contain convex lenses. For a distant object that is placed more than twice the focal length from the lens, the image is:. Projectors contain convex lenses. For an object placed between one and two focal lengths from the lens, the image is:. In a film or data projector, this image is formed on a screen. Film must be loaded into the projector upside down so the projected image is the right way up. A magnifying glass is a convex lens used to make an object appear much larger than it actually is.

This works when the object is placed at a distance less than the focal length. The image is:. Only the person using the magnifying glass can see the image. The image cannot be projected onto a screen because it is a virtual image. Concave lenses always produce images that are:. Peep holes are set into doors so the occupant can identify a visitor before opening the door. For an object viewed through a concave lens, light rays from the top of the object will be refracted and will diverge on the other side of the lens.

These rays will appear:. Real and virtual images The images formed by a lens can be: upright or inverted upside down compared to the object magnified or diminished smaller than the object real or virtual A real image is an image that can be projected onto a screen.

## Ray Diagrams for Lenses

To draw a ray diagram : Draw a ray from the object to the lens that is parallel to the principal axis. Once through the lens, the ray should pass through the principal focus. Draw a ray which passes from the object through the centre of the lens.The theme of this unit has been that we see an object because light from the object travels to our eyes as we sight along a line at the object. Similarly, we see an image of an object because light from the object reflects off a mirror and travel to our eyes as we sight at the image location of the object.

From these two basic premises, we have defined the image location as the location in space where light appears to diverge from. Ray diagrams have been a valuable tool for determining the path of light from object to mirror to our eyes. In this section of Lesson 3, we will investigate the method for drawing ray diagrams for objects placed at various locations in front of a concave mirror. To draw these diagrams, we will have to recall the two rules of reflection for concave mirrors:.

Earlier in this lesson, the following diagram illustrating the path of light from an object to mirror to an eye placed at various locations was shown. In this diagram five incident rays are drawn along with their corresponding reflected rays. Each ray intersects at the image location and then diverges to the eye of an observer.

Every observer would observe the same image location and every light ray would follow the law of reflection. Yet only two of these rays would be needed to determine the image location; since it only requires two rays to find the intersection point.

Of the five incident rays drawn, two of them correspond to the incident rays described by our two rules of reflection for concave mirrors. These will be the two rays used through the remainder of this lesson, merely because they are the easiest pair of rays to draw. The method of drawing ray diagrams for concave mirror is described below.

The description is applied to the task of drawing a ray diagram for an object located beyond the center of curvature C of a concave mirror. Using a straight edge, accurately draw one ray so that it passes exactly through the focal point on the way to the mirror. Draw the second ray such that it travels exactly parallel to the principal axis.

Place arrowheads upon the rays to indicate their direction of travel. The ray that passes through the focal point on the way to the mirror will reflect and travel parallel to the principal axis. Use a straight edge to accurately draw its path. The ray which traveled parallel to the principal axis on the way to the mirror will reflect and travel through the focal point. Extend the rays past their point of intersection. The image point of the top of the object is the point where the two reflected rays intersect.

If your were to draw a third pair of incident and reflected rays, then the third reflected ray would also pass through this point. This is merely the point where all light from the top of the object would intersect upon reflecting off the mirror. Of course, the rest of the object has an image as well and it can be found by applying the same three steps to another chosen point. See note below.

The goal of a ray diagram is to determine the location, size, orientation, and type of image which is formed by the concave mirror. Typically, this requires determining where the image of the upper and lower extreme of the object is located and then tracing the entire image. After completing the first three steps, only the image location of the top extreme of the object has been found.

Thus, the process must be repeated for the point on the bottom of the object. If the bottom of the object lies upon the principal axis as it does in this examplethen the image of this point will also lie upon the principal axis and be the same distance from the mirror as the image of the top of the object.Mini Physics.

This is a short tutorial on how to draw ray diagrams for plane mirrors. Click on the images to view a larger version. The image is virtual. Broken lines from the image to mirror indicate virtual rays. Virtual image: Light rays do not actually meet at the image position. Because of that, a virtual image cannot be projected on a screen.

Lines joining the object to the positions of the reflected rays on the mirror represent the incident rays. Administrator of Mini Physics. If you spot any errors or want to suggest improvements, please contact us.

Notify me of follow-up comments by email. Notify me of new posts by email. Reflection of light Drawing ray diagrams for plane mirrors Refraction of light Total internal reflection. Initially, we have an object in front of a plane mirror. First, we draw an image of the object on the other side of the mirror Distance A is equal to distance B and the image size is the same size as the object size. Second, we draw light rays from the image to the eye The image is virtual. Continuous lines from the mirror to eye indicate the reflected rays.

Properties of image formed in plane mirror: Same size as object Laterally inverted Left becomes right, right becomes left Upright Virtual As far behind the mirror as the object is in front. Mini Physics Administrator of Mini Physics.

Leave this field empty.The line of sight principle suggests that in order to view an image of an object in a mirror, a person must sight along a line at the image of the object. When sighting along such a line, light from the object reflects off the mirror according to the law of reflection and travels to the person's eye.

This process was discussed and explained earlier in this lesson. One useful tool that is frequently used to depict this idea is known as a ray diagram. A ray diagram is a diagram that traces the path that light takes in order for a person to view a point on the image of an object. On the diagram, rays lines with arrows are drawn for the incident ray and the reflected ray. Complex objects such as people are often represented by stick figures or arrows. In such cases it is customary to draw rays for the extreme positions of such objects.

This section of Lesson 2 details and illustrates the procedure for drawing ray diagrams. Let's begin with the task of drawing a ray diagram to show how Suzie will be able to see the image of the green object arrow in the diagram below. For simplicity sake, we will suppose that Suzie is viewing the image with her left eye closed.

Thus, we will focus on how light travels from the two extremities of the object arrow the left and right side to the mirror and finally to Suzie's right eye as she sights at the image. The four steps of the process for drawing a ray diagram are listed, described and illustrated below. Pick one extreme on the image of the object and draw the reflected ray that will travel to the eye as it sights at this point. Draw the incident ray for light traveling from the corresponding extreme on the object to the mirror.

The best way to learn to draw ray diagrams involves trying it yourself. It's easy. If necessary, refer to the four-step procedure listed above. When finished, compare your diagram with the completed diagrams at the bottom of this page. Ray diagrams can be particularly useful for determining and explaining why only a portion of the image of an object can be seen from a given location.

The ray diagram at the right shows the lines of sight used by the eye in order to see a portion of the image in the mirror. Since the mirror is not long enough, the eye can only view the topmost portion of the image. The lowest point on the image that the eye can see is that point in line with the line of sight that intersects the very bottom of the mirror.

As the eye tries to view even lower points on the image, there is not sufficient mirror present to reflect light from the lower points on the object to the eye. The portion of the object that cannot be seen in the mirror is shaded green in the diagram below. Similarly, ray diagrams are useful tools for determining and explaining what objects might be viewed when sighting into a mirror from a given location. For example, suppose that six students - Al, Bo, Cy, Di, Ed, and Fred sit in front of a plane mirror and attempt to see each other in the mirror.

## SS: Ray Diagrams For Converging Lens

And suppose the exercise involves answering the following questions: Whom can Al see? Whom can Bo see? Whom can Cy see? Whom can Di see? Whom can Ed see? And whom can Fred see? The task begins by locating the images of the given students. Then, Al is isolated from the rest of the students and lines of sight are drawn to see who Al can see. The leftward-most student whom Al can see is the student whose image is to the right of the line of sight that intersects the left edge of the mirror. This would be Ed.These three rules will be used to construct ray diagrams. A ray diagram is a tool used to determine the location, size, orientation, and type of image formed by a lens. Ray diagrams for double convex lenses were drawn in a previous part of Lesson 5.

In this lesson, we will see a similar method for constructing ray diagrams for double concave lenses. Pick a point on the top of the object and draw three incident rays traveling towards the lens. Once these incident rays strike the lens, refract them according to the three rules of refraction for double concave lenses. Some students have difficulty understanding how the entire image of an object can be deduced once a single point on the image has been determined.

If the object is merely a vertical object such as the arrow object used in the example belowthen the process is easy. The image is merely a vertical line. This is illustrated in the diagram below. In theory, it would be necessary to pick each point on the object and draw a separate ray diagram to determine the location of the image of that point. That would require a lot of ray diagrams as illustrated in the diagram below. Fortunately, a shortcut exists.

If the object is a vertical line, then the image is also a vertical line. For our purposes, we will only deal with the simpler situations in which the object is a vertical line that has its bottom located upon the principal axis.

For such simplified situations, the image is a vertical line with the lower extremity located upon the principal axis. The ray diagram above illustrates that the image of an object in front of a double concave lens will be located at a position behind the double concave lens. Furthermore, the image will be upright, reduced in size smaller than the objectand virtual. This is the type of information that we wish to obtain from a ray diagram. The characteristics of this image will be discussed in more detail in the next section of Lesson 5.

Once the method of drawing ray diagrams is practiced a couple of times, it becomes as natural as breathing. Each diagram yields specific information about the image. It is suggested that you take a few moments to practice a few ray diagrams on your own and to describe the characteristics of the resulting image. The diagrams below provide the setup; you must merely draw the rays and identify the image. If necessary, refer to the method described above.

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