When describing an image, state if image is
-
- real or virtual
- upright or inverted
- magnified, diminished or same size
If required the value of magnification can be calculated. Magnification is the ratio of image height to object height. A magnification of 3 means the image is 3 times as large as the object. A magnification of 0.5 means that the image is half the height of the object.
v/u is usually a preferred method to calculate the magnifications,m, as u and v are usually larger than hi and ho and thus produce a value of m with a greater precision.
Note: Similar triangles (maths topic) applied here.
(a) Object is closer to the lens than F (u < ƒ)
Image is virtual, erect and enlarged.
The image is on the same side of the lens as the object.
v > u
(b) Object is at the focal point F (u = ƒ)
Image is inverted and enlarged.
The image is on the opposite side of the lens as the object.
v = ∞
(c) Object is between F and 2F (ƒ< u < 2ƒ)
Image is real, inverted and enlarged.
The image is on the opposite side of the lens as the object.
2ƒ < v < ∞
(d) Object is at 2F (u = 2ƒ)
Image is real, inverted and same size.
The image is on the opposite side of the lens as the object.
v = 2ƒ
(e) Object is beyond 2F (2ƒ< u < ∞)
Image is real, inverted and diminished.
The image is on the opposite side of the lens as the object.
ƒ < v < 2ƒ
(f) Object is at infinity (u = ∞)
Image is real, inverted and diminished.
The image is on the opposite side of the lens as the object.
v = ƒ
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