# EMF induced in a rotating rod having mass

#### Physics lover

Homework Statement
The question is put in Attempt at a solution.
Homework Equations
emf induced in a rotating rod = Bwr$^2$/2

I first calculated induced emf and then calculated torque about O.But what will i do further.I think i need to find current and then fidn emf=IR.
Help please.

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#### kuruman

Science Advisor
Homework Helper
Gold Member
Please show your work. It is supposed to go in "Attempt at a solution" but now it has to go in separate post. Ask yourself, "What does it mean to have the rod rotate at constant angular velocity?"

#### Physics lover

Please show your work. It is supposed to go in "Attempt at a solution" but now it has to go in separate post. Ask yourself, "What does it mean to have the rod rotate at constant angular velocity?"
it means that there is not external torque that is torque of mg is balanced by torque of induced current.

#### Physics lover

Please show your work. It is supposed to go in "Attempt at a solution" but now it has to go in separate post. Ask yourself, "What does it mean to have the rod rotate at constant angular velocity?"
i have shown how much i have proceeded far.Now i cannot do it further.

#### kuruman

Science Advisor
Homework Helper
Gold Member
It means that there is not external torque that is torque of mg is balanced by torque of induced current.
And where is the equation that says that? Parenthetically, there are two external torques. What you meant to say is that there is no net torque. Right? This is a torque balance problem. What does one normally do with such problems? Hint: Free body diagram.

#### Physics lover

And where is the equation that says that? Parenthetically, there are two external torques. What you meant to say is that there is no net torque. Right? This is a torque balance problem. What does one normally do with such problems? Hint: Free body diagram.
ok i think i got that.The emf to be find out will have its own torque =IBL which will balance the torque of mg and induced current.Am i right?

#### kuruman

Science Advisor
Homework Helper
Gold Member
ok i think i got that.The emf to be find out will have its own torque =IBL which will balance the torque of mg and induced current.Am i right?
You are right except that IBL is a force, not a torque.

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