When to Approximate (Electrostatics and in general :p)

[low lava]

first off happy new to yall.
now in this q, 2 cm = 20 mm is a comparable distance to the radii of the given spheres (25%). so ideally when we equate potential at surface, we should write (Q = charge on A after eqbm, Q' = charge on B after eqbm):

kQ/5 + kQ'/15 = kQ/10 + kQ'/10 which gives Q = Q'/3
(i.e account for mutual potential)
however when u solve this no option matches. when i checked eduniti he said we can ignore this distance. when u solve that u get Q = Q'/2 (drastic difference)

i take <5% or <10% a measure for approxmation. so my doubt is when do i safely approximate and when do i dont.

When to Approximate (Electrostatics and in general :p)

[upbeat talon]

<@&1227987967939838003>

Note for OP

+solved @user1 @user2... to close the thread when your doubt is solved. Mention the users who helped you solve the doubt. This will be added to their stats.

[low lava]

im guessing this is fault on NTA's side?

[gilded sonnet]

while attempting an exam dont think ques / options is wrong . if u r making some assumption while solving the ques and no ans matches then it just means your assumption is wrong and u should try again. tb bhi nahi match kare toh just leave and move on

[low lava]

ok

+solved @gilded sonnet