All Solutions
Page 618: Lesson Check
$$
frac{1}{f}=frac{1}{d_0}+frac{1}{d_i}.
$$
b) I would be smaller and the explanation is the same as in a). Namely, if it intersects with it closer it will also intersect lower and make a smaller image.
$$
begin{align*}
d_o &= 32 text{ cm} \
d_i &= 17 text{ cm}
end{align*}
$$
The focal length of the lens can be calculated by applying the thin-lens equation to the problem :
$$
{dfrac{1}{d_o} + dfrac{1}{d_i} = dfrac{1}{f}}
$$
$$
{f = dfrac{1}{dfrac{1}{d_o} + dfrac{1}{d_i}}}
$$
$$
{f = dfrac{1}{dfrac{1}{32 text{ cm}} + dfrac{1}{17 text{ cm}}}}
$$
$$
{boxed{f = 11.1 text{ cm}}}
$$
{f = 11.1 text{ cm}}
$$
$$
begin{align*}
d_o &= 29 text{ cm} \
f &= 15 text{ cm}
end{align*}
$$
The image distance of the object can be calculated by applying the thin-lens equation to the problem :
$$
{dfrac{1}{d_o} + dfrac{1}{d_i} = dfrac{1}{f}}
$$
$$
{d_i = dfrac{1}{dfrac{1}{f} – dfrac{1}{d_o}}}
$$
$$
{d_i = dfrac{1}{dfrac{1}{15 text{ cm}} – dfrac{1}{29 text{ cm}}}}
$$
$$
{boxed{d_i = 31.07 text{ cm}}}
$$
{d_i = 31.07 text{ cm}}
$$
$$
begin{align*}
d_i &= – 12 text{ cm} \
f &= – 23 text{ cm}
end{align*}
$$
The distance of the object from the focal point can be calculated by applying the thin-lens equation to the problem :
$$
{dfrac{1}{d_o} + dfrac{1}{d_i} = dfrac{1}{f}}
$$
$$
{d_o = dfrac{1}{dfrac{1}{f} – dfrac{1}{d_i}}}
$$
$$
{d_o = dfrac{1}{dfrac{1}{- 23 text{ cm}} + dfrac{1}{12 text{ cm}}}}
$$
$$
{boxed{d_o = 25.1 text{ cm}}}
$$
{d_o = 25.1 text{ cm}}
$$