# Induced EMF and long steel beam

1. Apr 10, 2006

### Punchlinegirl

A 5.97 m long steel beam is accidentally dropped by a construction crane from a height of 6.82 m. The horizontal component of the Earth's magnetic field over the region is 12.2 $$\mu T$$. The acceleration of gravity is 9.8 m/s^2. What is the induced emf in the beam just before impact with the Earth, assuming its long dimension remains in a horizontal plane, oriented perpendicularly to the horizontal component of the Earth's magnetic field? Answer in units of mV.

I know that E= change in flux/change in time
To get the change in time I used the equation
x(t)= x_o +v_o*t +.5 gt^2
where x_o=v_o=0
and x(t)= 6.82 m.
solving for t gave me .834 s.
Then for the flux I think it's just B*L= 72.8... but I don't think thats right...

2. Apr 10, 2006

### Chi Meson

review something called "motional emf." THere is a variation of the emf formula for a straight conductor moving through a magnetic field in terms of its speed. Then, all you need to do is find the speed of the bar as it reaches the ground.

3. Apr 10, 2006

### Punchlinegirl

I got it... Thanks!