1 question

The lens formula is:

$${\frac{{\mathtt{1}}}{{\mathtt{f}}}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{1}}}{{\mathtt{d1}}}} = {\frac{{\mathtt{1}}}{{\mathtt{d2}}}}$$

In which

f: focal length

d1:distance to source

d2:distance to image

 

Since the sun has an almost infinite distance to the lens d1=infinity, which means:

 $${\frac{{\mathtt{1}}}{{\mathtt{\infty}}}} = {\mathtt{0}}$$

so

 $${\frac{{\mathtt{1}}}{{\mathtt{f}}}} = {\frac{{\mathtt{1}}}{{\mathtt{d2}}}}$$

 

Which means answer A is correct.