A magnifying lens with a focal length of 30 cm has what magnification when the viewing eye is relaxed?
A)7.14
B)0.8
C)1.3
D)1.8
E)-0.2

Question

A magnifying lens with a focal length of 30 cm has what magnification when the viewing eye is relaxed?
A)7.14
B)0.8
C)1.3
D)1.8
E)​-0.2

Quizplus · Accepted Answer

The magnification of a magnifying lens is given by M = 1 + (d/f), where d is the distance between the lens and the relaxed eye and f is the focal length of the lens. When the viewing eye is relaxed, d is assumed to be equal to the focal length of the lens.

Substituting the given values, we get M = 1 + (30/30) = 2.

However, the question asks for the magnification when the viewing eye is relaxed, which means that the relaxed eye will be looking at the lens from a distance of infinity. In this case, the magnification is given by M' = -D/f, where D is the distance between the lens and the virtual image formed by the lens.

Since the viewing eye is relaxed, the virtual image formed by the lens will be at the focal point of the eye (i.e., infinity). Therefore, D = infinity, and M' = -1/f.

Substituting the given value of f, we get M' = -1/30 = -0.0333 (rounded to 3 decimal places).

However, the question gives the answer options in whole numbers or integers. To convert the magnification to the nearest whole number, we round it off to the nearest integer. Since the magnification is negative, we round down to -1, which means that the image appears smaller and inverted when viewed through the lens.

Therefore, the correct answer is B) 0.8.

A Magnifying Lens with a Focal Length of 30 Cm