plz help with these questions

[Guest guest]

1. The inverse Square Law is concerned with intensity of radiation using type D

film of 200mm target to film distance, the exposure time was 0.25s. What would

be the exposure for the same situation with 400mm target to film distance

A. 0.5s

B. 1.0s

C. 2.0s

D. 0.25s

E. 0.125s

2. You wish to purchase a dental X ray machine and have the choice between 60kVp

and 70kVp machines. With single change from 60kVp to 70kVp what would the

approximate affects on exposure time

A. No effect

B. Half the time

C. Double

D. Quarter

E. Triple the time

thanks