I HAVE THIS QUESTION POSTED TWICE SO THERE IS A TOTAL OF 350 POINTS The scenario

Question

I HAVE THIS QUESTION POSTED TWICE SO THERE IS A TOTAL OF 350 POINTS
The scenario for this estimate is a person wearing a gold ring who is just missed by a lightning strike.

Estimate:



Ring's resistance: imagine cutting through one side of a ring so it can be straightened out into a short, fat strip of gold: a “wire”. Make reasonable assumptions about the length and cross section of this strip and use your assumptions to calculate an estimate of the ring's resistance.


Bolt's magnetic field: do a little research on the internet to find out how much current lightning bolts can deliver, and choose a current that falls somewhere within the range of “ normal” lightning currents. Decide how far away from the bolt you want person wearing the ring to be, and assuming that the bolt is like a long-straight wire carrying a current, calculate the magnitude of the magnetic field generated by the bolt at the ring's location.


Induced emf: based on a reasonable length for the duration of the lightning bolt, the magnetic field estimated already, and the assumed radius of the ring, calculate the emf induced in the ring by the lightning bolt.


Current: put together what you've got so far and calculate an estimate of the current induced in the ring by the lightning bolt.

Be sure to justify each of your assumptions briefly, explain your calculations briefly, and show your work.

Explanation / Answer

A) Resistance of the ring is             R = L / A                               ...... (1) Here L is Length of the strip , A is the area of crossection of strip and is the resistivity of gold.   _________________________________________________________________________ B) Magnitude of the magnetic field generated by the bolt at the ring's location.           B = o I / 2r  
Here I is the current passing through the bolt and r is radius of ring.
________________________________________________________________________

C) Emf induced in the ring by the lightning bolt           = d / dt              = d/dt ( BA )              = d/ dt [(  o I / 2r) (r2 )              = d/dt ( o Ir / 2)
             = (o r / 2)dI/dt
________________________________________________________________________

D)
Current induced in the ring by lightining bolt          I = /R
From equation (1)
          I = / ( L / A)              = A /L

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