In fig. battery E is balanced on 55cm length of potentiometer wire but when a resistance of `10Omega` is connected in parallel with the battery then it balances on 50cm length of the potentiometer wire then internal resistance r of the battery is:-

Options

A. `4.2`
B. `7.6`
C. `5.6`
D. `6.8`

Answer

D

Explanation

When 'm' leavers the wedge 'M' then wedge moves distance 'x' in left side
`:. M (4 - x) = Mx rArr = 0.8 m`
`:.` Co-ordinate where block will be leave wedge
`x = 4 - 0.8 = 3.2`
Time for m will strike the ground is `= sqrt((2 xx 2)/(10))`
`:. x_(f) = 3.2 + 4 sqrt2 xx (2)/(sqrt10) = 6.8 m`