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.

What is the largest voltage the battery can have without breaking the circuit at the supports?

Options

A. `817V`
B. `412V`
C. `325V`
D. `160V`

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`