A thin, 50 cm long metal bar with mass 750 g rests on, but is not attrached to, two metallic supports in a uniform 0.450T magnetic field, as shown in fig. A battery and a `25Omega` resistor in series are connected to the supports.

The battery voltage has the maximum value calculated in above question. If the resistor suddenly gets partially short-circuited, decreasing its resistance to `2 Omega`, find the initial accleration of the bat.

Options

A. `113ms^-2`
B. `55ms^-2`
C. `180ms^-2`
D. `12.4ms^-2`

Answer

a

Explanation

(a) `F_1=mg`
When bar is just ready to levitate,
`IlB=mg, I=(mg)/(lB)=((0.75kg)(9.80m//s^2))/((0.500m)(0.450T))=32.67T`
`epsilon=IR=(32.67A)(25.0Omega)=817V`
(b) `R=2.0Omega, I=epsilon/R=(817V)(2.0Omega)=408.5A`
`F_1=IlB=92N`
`a=(F_1-mg)//a=113ms^-2`