How to Draw Refraction Ray Diagrams

In this explainer, we volition learn how to draw diagrams of light rays interacting with convex lenses.

A convex lens focuses parallel low-cal rays at a focal point. This is shown in the following figure.

The directions of light rays that pass through the lens depend on two rules.

The offset rule applies to any lite ray that passes through the lens.

Rule: Refraction of Light Rays on the Optical Axis of a Convex Lens

Any light ray that passes through the centre of a convex lens does non change management.

The 2d dominion applies to light rays that are parallel to the optical centrality before they achieve the lens and that do non laissez passer through the middle of the lens.

Recall that the optical centrality of a convex lens is an imaginary line that passes through the center of curvature of the lens and through the widest part of the lens, as shown in the following figure.

Rule: Refraction of Light Rays off the Optical Centrality of a Convex Lens

A calorie-free ray that is parallel to, simply not along, the optical centrality volition change direction when information technology passes through a convex lens. The direction of the calorie-free ray will modify so that the ray passes through the focal point of the lens that is on the reverse side of the lens to the side that light enters the lens from.

Permit u.s. look at some examples involving light rays passing through a convex lens.

Example 1: Identifying the Effect of a Convex Lens on the Paths of Parallel Light Rays

Which of the following diagrams shows what happens when parallel light rays laissez passer through a thin convex lens?

Answer

Choice 2 shows a convex lens that has no result on the paths of light rays. Nosotros come across that these lite rays do not cantankerous each other. This means that these rays do not all pass through a single indicate, which they must do when shown correctly.

Pick i shows the low-cal rays changing management. Nosotros see, though, that these low-cal rays likewise do non cross each other. This means that these rays practise not all pass through a single signal, which they must do when shown correctly.

Option 5 shows the light rays changing management. We see likewise that these lite rays all cantankerous each other. Nonetheless, the calorie-free rays do not all cantankerous each other at the aforementioned point, which they must do when shown correctly.

Option three shows parallel lite rays spreading out afterwards passing through the lens. This would not occur for a convex lens.

The correct respond is choice 4, as this shows the low-cal rays all crossing at a single indicate, which is the focal betoken of the lens.

Example 2: Identifying the Path of a Light Ray That Passes through a Convex Lens

Each of the following diagrams shows a ray entering a sparse convex lens. The point marked P is the focal point of the lens. Earlier the ray enters the lens, it is parallel to the optical axis and information technology passes through the centre of the lens. Which diagram correctly shows the path of the ray afterward it passes through the lens?

Answer

Any light ray that passes through the eye of a lens does not modify direction. In options 2 and 3, the light ray passes through the center of the lens and changes direction.

Only option 1 shows the light ray non changing direction. Information technology is the right option.

Example 3: Identifying the Path of a Light Ray That Passes through a Convex Lens

Each of the following diagrams shows a ray entering a thin convex lens. The bespeak marked P is the focal point of the lens. Before the ray enters the lens, information technology is parallel to the optical axis and it passes through the center of the lens. Which diagram correctly shows the path of the ray after it passes through the lens?

Answer

The calorie-free ray that enters the lens is parallel to the optical axis but not along the optical centrality. This ray does not pass through the center of the lens. The ray must then alter direction to laissez passer through the focal point of the lens.

Only option two shows this lite ray passing through the focal signal though, so information technology is the correct option.

The distance from the center of the lens to the focal point is chosen the focal length.

If an object is further from a convex lens than the focal length of the lens, the light rays from the object that pass through the lens will form an image on the opposite side of the lens to the object.

The image formed can be projected onto a screen. This kind of paradigm is chosen a real epitome. The formation of an image is shown in the following figure.

The diagram showing the image is produced by comparison two light rays from the top of the object: a calorie-free ray that is parallel to the optical axis and a lite ray that passes through the center of the lens.

Let united states of america at present look at an example involving a light ray that passes through the center of a convex lens just not along the optical axis.

Instance four: Identifying the Path of a Light Ray That Passes through a Convex Lens but Not along the Optical Axis

Each of the following diagrams shows a ray entering a thin convex lens. The point marked P is the focal indicate of the lens. The ray passes through the center of the lens. Which diagram correctly shows the path of the ray after it has passed through the lens?

Answer

A light ray that passes through the center of a lens will not change management. This is truthful whether or not the ray is along the optical axis.

This is simply shown in option 3, which is the correct choice.

We run across that two low-cal rays from the height of the object, after passing through the lens, eventually accomplish the same bespeak.

This is actually true for light rays from the top of the object that travel in any direction, assuming that these rays starting time pass through the lens.

What is true for calorie-free rays from the top of the object is truthful for all the other points on the object. This means that every point of the object appears in the image.

It is of import to find that the top of the object is higher up the optical axis of the lens. The top of the prototype is beneath the optical centrality of the lens. This ways that the image is upside down compared to the object. The prototype is inverted.

The point at which the image tin can be seen depends on the focal length of the lens and the distance of the object from the lens.

Changing the distance of the object from the lens changes the distance of the image from the lens.

The size of the image also changes when the distance between the object and the lens changes.

These changes are shown in the following figure.

We encounter that when the distance betwixt the object and the lens is greater than twice the focal length, the epitome is smaller than the object.

For distances greater than twice the focal length, moving the object further from the lens will make the prototype smaller. Moving the object nearer the lens will make the image size become closer to the object size.

At exactly twice the focal length, the object and prototype will be of equal sizes.

When the distance between the object and the lens is greater than the focal length just less than twice the focal length, the image is larger than the object. This ways that the epitome is magnified. Moving the object closer to the focal bespeak will make the image larger, increasing the magnification.

This following figure shows what happens when the object is at the focal length of the lens.

The calorie-free rays from the top of the object are parallel after they exit the lens. These rays practise not cross each other.

One fashion of describing this is that the paradigm formed by this lens forms infinitely far from the lens. This means that for any finite altitude from the lens, no image is formed.

The object can still be moved closer to the lens, nonetheless.

If the object is moved closer to the lens than the focal length, the ii rays that were parallel when the object was at the focal length increment their distance from each other the greater their altitude from the lens. This is shown in the post-obit figure.

The fact that these rays increase the distance between them in the infinite to the correct of the lens ways that the altitude between the paths of these rays must decrease if they were extended into the space to the left of the lens. This is shown in the following figure.

At a point to the left of the object, the extended paths of the rays that exit the lens see.

The new point is the top of another image that the lens can produce. This is shown in the post-obit figure.

The image formed is not a real image. Information technology cannot be projected on a screen. Information technology is a virtual image. Such an image can be seen, though, by a man middle.

Nosotros see that the virtual image is on the same side of the lens as the object, further from the lens than the object.

We too see besides that the virtual image is larger than the object.

Moreover, we see that the directions of light rays from the top of the object afterwards passing through the lens are the aforementioned equally the directions of the lines from the height of the virtual epitome to the lens.

This means that the virtual image is the same manner up as the object.

Let us now summarize what we take learned in this explainer.

Key Points

• A convex lens can focus parallel light rays that pass through it at a focal bespeak.
• The distance from the lens to the focal bespeak is the focal length of the lens.
• A convex lens but focuses light rays at a indicate if these rays outset from a bespeak farther from the lens than the focal length of the lens.
• An object at a altitude from the lens greater than the focal length produces a real prototype on the opposite side of the lens to the object.
• The real image formed by a convex lens is inverted.
• The distance of the object from a convex lens and the focal length of the lens decide the size and the position of the real epitome formed. The real image may be either larger than, smaller than, or equal in size to the object.
• An object at a distance from a convex lens less than the focal length produces a virtual image rather than a existent image.
• The virtual image formed by a convex lens is the same way upwardly every bit the object that produces it.
• The virtual image formed by a convex lens is larger than the object that produces information technology.

How to Draw Refraction Ray Diagrams

Source: https://www.nagwa.com/en/explainers/789129537830/

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