1) Describe formation of image by a converging lens. Include: a) what is an imag
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Question
1) Describe formation of image by a converging lens. Include:
a) what is an image;
b) what is the focal point of a converging lens;
c) what is the focal point of a diverging lens;
d) the thin-lens equation (the thin lens equation is the one that relates distance to the image and distance to the object through the focal length of a lens);
e) lateral magnification.
f) Describe a real image formed by a converging lens (whether it is inverted or not inverted relative to the object, whether it is enlarged or reduced, where an object should be located relative to the lens for its image to be real, etc.).
g) Describe an image formed by a single converging lens (whether it is inverted or not inverted relative to the object, whether it is enlarged or reduced, whether it is real or virtual, etc).
h) Describe how to find a theoretical location of an image produced by a combination of a converging and a diverging lens. Explain which parameters you need to know and/or to measure to be able to do this.
2) Solve the following problem:
A converging lens creates a real image of an object. If object distance is 10.0 cm and image distance is 15.0 cm, find:
- Focal length of the lens;
- Lateral magnification of the image;
- Image distance when object distance is 15.0 cm.
Explanation / Answer
1) Formation of image by converging lens
a) Real images are produced when the object is located a distance greater than one focal length from the lens. A virtual image is formed if the object is located less than one focal length from the converging lens
b) A converging lens (or convex lens) is curved on both sides. This means the light rays coming out of it come together at a point – they converge. The point at which the light rays meet is called the focal point. The focal length is found by focussing a distant object on a piece of paper through the lens.
c) The focal point of a concave lens is the point where light rays parallel to the axis seem to diverge from after passing through the lens. The distance from the lens to this point is called the focal length of the lens.
d) (1/o)+(1/i) = 1/f
where, o is object distance
i is image distance
f is focal length
If the lens equation yields a negative image distance, then the image is a virtual image on the same side of the lens as the object. If it yields a negative focal length, then the lens is a diverging lens rather than the converging lens in the illustration.
e) The lateral magnification of the image is M=h'/h = -q/p. When M is positive, the image is upright and on the same side of the lens as the object. When M is negative, the image is inverted and on the side of the lens opposite the object. Converging lenses have positive focal lengths.
f) a real image is one that is formed when the outgoing rays form a point converging at a real location.
Real images can be produced by concave mirrors and converging lenses, only if the object is placed further away from the mirror/lens than the focal point and this real image is inverted.
g) A converging lens will only produce a virtual image if the object is located in front of the focal point. ... A converging lens produced a virtual image when the object is placed in front of the focal point. For such a position, the image is magnified and upright, thus allowing for easier viewing.
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