Question

Two lenses of focal length 4.5cm and 1.5cm are placed at a certain distance apart, calculate the distance between the lenses if they form an achromatic combination
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Answer 1

Answer:

3.0cm

Explanation:

For lenses in an achromatic combination, the following condition holds, assuming the two lenses are of the same materials;

d = $\frac{f_1 + f_2}{2}$     ---------(i)

Where;

d= distance between lenses

f₁ = focal length of the first lens

f₂ = focal length of the second lens

From the question;

f₁ = 4.5cm

f₂ = 1.5cm

Substitute these values into equation (i) as follows;

d = $\frac{4.5+1.5}{2}$

d = $\frac{6.0}{2}$

d = 3.0cm

Therefore, the distance between the two lenses is 3.0cm