A convex lens of focal length 25cm and a concave lens of focal length 10cm are placed in close contact with one another.
- What is the power of this combination?
- What is the focal length of this combination?
- Is this combination converging or diverging?
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$\text{f}_1=25\text{cm}=0.25\text{m}$$\text{P}_1=\frac{1}{\text{f}_1}=\frac{1}{0.25}=4\text{D}$
$\text{f}_2=-10\text{cm}=-0.1\text{m}$
$\text{P}_2=\frac{1}{\text{f}_2}=\frac{1}{-0.1}=-10\text{D}$
$=4\text{D}+(-10\text{D})$
$=-6\text{D}$
$\text{f}_2=-10\text{cm}=-0.1\text{m}$
$\text{P}_2=\frac{1}{\text{f}_2}=\frac{1}{-0.1}=-10\text{D}$
- Power of the combination,
$=4\text{D}+(-10\text{D})$
$=-6\text{D}$
- Focal length of the combination,
- The combination has negative focal length, so it is diverging.
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