# lens

## convex lens

A convex lens is thicker in the middle than at the edges. You can see the shape of a convex lens in the Figure 1.2. A convex lens causes rays of light to converge, or meet, at a point called the focus (F). A convex lens forms either a real or virtual image. It depends on how close the object is to the lens relative to the focus. Q: An example of a convex lens is a hand lens. Which of the three convex lens diagrams in the Figure 1.2 shows how a hand lens makes an image? A: Youve probably looked through a hand lens before. If you have, then you know that the image it produces is right-side up. Therefore, the first diagram must show how a hand lens makes an image. Its the only one that produces a right-side up image.

## concave lens

A concave lens is thicker at the edges than it is in the middle. You can see the shape of a concave lens in the Figure Note that the image formed by a concave lens is on the same side of the lens as the object. It is also smaller than the object and right-side up. However, it isnt a real image. It is a virtual image. Your brain tricks you into seeing an image there. The light rays actually pass through the glass to the other side and spread out in all directions.

## what is a lens

A lens is a transparent object with one or two curved surfaces. It is typically made of glass (or clear plastic in the case of a contact lens). A lens refracts, or bends, light and forms an image. An image is a copy of an objected formed by the refraction (or reflection) of visible light. The more curved the surface of a lens is, the more it refracts the light that passes through it. There are two basic types of lenses: concave and convex. The two types of lenses have different shapes, so they bend light and form images in different ways.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

a lens reflects light and forms an image.

``````a. true

-->  b. false
``````

the less curved the surface of a lens is, the more the lens refracts light.

``````a. true

-->  b. false
``````

the image of an object formed by a concave lens is always

``````a) on the same side of the lens as the object.

b) smaller than the object.

c) right-side up.

-->  d) all of the above
``````

a concave lens forms only real images.

``````a. true

-->  b. false
``````

a convex lens forms a virtual image when the object is

``````-->  a) closer to the lens than the focus is.

b) farther from the lens than the focus is.

c) the same distance from the lens as the focus is.

d) on the opposite side of the lens from the focus.
``````

## diagram questions

No diagram questions associated with this lesson