ACT science practice test 42

Directions: Each passage is followed by several questions. After reading a passage, choose the best answer to each question and fill in the corresponding oval on your answer document. You may refer to the passages as often as necessary.

You are NOT permitted to use a calculator on this test.


Lenses are made of transparent materials such as glass and plastic and are used in eyeglasses, cameras, and telescopes, as well as other applications. When light rays enter a curved lens from a distant object, the rays are bent into new angles. A convex lens, which is thicker in the middle, takes parallel light rays and converges them toward a common point called the focal point. The focal length is defined as the distance from the center of the lens to the point where the bent rays converge. A concave lens, on the other hand, is thinner in the middle and diverges parallel light rays as if they came from a point ahead of the lens (this point is one focal length from the lens). Both lenses are shown in Figure 7.1.

Figure 7.1

In conventional ray diagrams, the source of light (the object) is to the left of the lens and the rays move to the right through the lens. Light rays leave objects at various angles and are bent by the lens to form an image of the distant object. Real images are formed when actual light rays converge to a common point to the right of the lens. Virtual images are formed when the observer looks backward through the lens and sees an image on the same side of the lens as the object. Table 7.1 summarizes the images observed by these lenses.

TABLE 7.1

1. When the human eye views distant objects, the light rays go through a lens that is thicker in the middle. An image forms on the retina, which is the inner back surface of the eye. Which of the following best identifies the eye's lens and the characteristics of the image?

A. Convex; real, inverted, and smaller
B. Concave; virtual, upright, and smaller
C. Convex; virtual, upright, and larger
D. Concave; real, inverted, and smaller

2. According to the information provided in the passage and Table 7.1, which of the following statements is true?

A. A lens that is thinner in the middle is capable of forming inverted images.
B. Convex lenses form a real image when the object is one focal length to the left of the lens.
C. Concave lenses can form images with many characteristics.
D. All real images are inverted.

3. A particular convex lens in a camera has a focal length of 10 cm. If the object for the picture is 30 cm from the lens, what type of image will form on the film?

A. A real, inverted, smaller image
B. A real, inverted, larger image
C. A real, inverted, same-size image
D. A virtual, upright, smaller image

4. Rays of light from the distant sun reach the earth nearly parallel with each other. A child wishes to take these rays of light and use them to burn a piece of paper. What type of lens should the child use, and how far from the center of the lens should the paper be?

A. A convex lens two focal lengths away from the paper
B. A concave lens two focal lengths away from the paper
C. A convex lens one focal length away from the paper
D. A concave lens one focal length away from the paper

5. A slide projector uses a convex lens with a focal length of 120 mm. A small picture on a transparent slide is placed upside down in the projector, 125 mm in front of the lens. What will the image on the screen look like?

A. Larger than the slide and right side up
B. Larger than the slide and upside-down
C. Same size as the slide and right side up
D. Same size as the slide and upside-down

6. Eyeglass lenses may be used to correct both nearsighted and farsighted vision. Someone who is farsighted has difficulty seeing tiny objects that are close to the lens. As farsighted patients look through corrective lenses toward the object, they are able to see a larger image clearly on the same side of the lens as the object. What type of lens corrects farsighted vision, and what is the orientation of the image to that of the object?

A. Convex; inverted
B. Convex; upright
C. Concave; inverted
D. Concave; upright

7. A copy machine has a lens with a focal length of 30 cm. How far from the lens must a document (the object) be placed if the copy (the image) is to be exactly the same size?

A. More than 60 cm from the lens
B. 60 cm from the lens
C. Between 30 and 60 cm from the lens
D. 30 cm from the lens

8. A child looks through a lens at the distant trees, and the trees still look distant but appear smaller. What type of lens is the child looking through, and is the image upright or inverted?

A. Convex; upright
B. Convex; inverted
C. Concave; upright
D. Concave; inverted

9. A 15-cm focal-length lens is used to focus a sharp image on a piece of paper that is 20 cm to the right of the lens. What information is known about the lens and the object?

A. The lens is convex, and the object is 30 cm to the left of the lens.
B. The lens is concave, and the object may be any distance from the lens.
C. The lens is convex, and the object is between 15 and 30 cm to the left of the lens.
D. The lens is convex, and the object is more than 30 cm to the left of the lens.

10. In Figure 7.2, Point "F" represents the focal point of the lens. If the candle is placed as shown in the figure, what type of image will be seen?


Figure 7.2

A. A real, inverted, smaller image
B. A real, inverted larger image
C. A virtual, upright, larger image
D. A virtual, upright, smaller image