Question

O lentila convergenta are dublul distantei focale de 1m. In fata lentilei la distanta de 5m se aseaza un bec electric. La ce distanta de lentila se formeaza imaginea?

Answer 1

2f=1m=>f=0.5m
folosesti legea lentilelor 
1/x1+1/x2=1/f    tie trebuindu ti x2
1/5+1/x2=1/0.5
1/5+1/x2=2/1
1+5/x2=10
5/x2=9
x2=5/9
   =0.555 m verifica calculele eventual

Answer 2

Se da:
2f=1m⇔f=0,5m
u=5m
v=?m

Formule:
[tex] \frac{1}{u} + \frac{1}{v}= \frac{1}{f} \\ \frac{1}{v} = \frac{1}{f} - \frac{1}{u} \\ \frac{1}{v} = \frac{u-f}{f*u} \\ v= \frac{f*u}{u-f} \\ Calcule:\\ v= \frac{0,5*5}{5-0,5}=0,(5)m[/tex]