A) Greater than 40 cm
B) Equal to 40 cm
C) Equal to 10 cm
D) Less than 10 cm
Correct Answer: A
Solution :
Using \[P={{P}_{1}}+{{P}_{2}}-d\times {{P}_{1}}{{P}_{2}}\] for equivalent power to be negative \[d\times {{P}_{1}}{{P}_{2}}>{{P}_{1}}+{{P}_{2}}\] Þ \[d\times 25>10\] Þ \[d>\frac{10}{25}m\] Þ \[d>\frac{10\times 100}{25}\] Þ \[d>40cm.\]
You need to login to perform this action.
You will be redirected in
3 sec
