How to calculate the time over which flux changes

[poortech]

1. if the magnetic flux linking all the turns of a 50 turn coil changes from 10 mWB to 20 mWB and induces an e.m.f. of 62.5 V in the coil, calculate the time over which the flux changes.

i know the formula to calculate the flux which is

E = -N change in flux / change in time.

to calculate the change in time we just need to change E with change in time in the formula, but by doing this answer will be negative which is not possible as time can not be negative. how to get rid of this -ve. or is it ok if i don't use it at all.


my answer is -0.008 Sec.

Homework Equations

The Attempt at a Solution

 

[rude man]

The 62.5V polarity was not defined with respect to coil geometry so your answer is correct when made positive.

 

[szynkasz]

62.5 V is an absolute value of e.m.f

 

[poortech]

thnx a lot guyz... :D

 

[Nickie]

To calculate the time over which the flux changes, we can use the formula E = -N(change in flux/change in time). In this case, we know the change in flux (10 mWB to 20 mWB) and the induced e.m.f. (62.5 V), so we can rearrange the formula to solve for the change in time: change in time = -E(change in flux)/N. Plugging in the values, we get change in time = -(62.5 V)(10 mWB - 20 mWB)/50 turns = 0.008 seconds.

However, as you mentioned, this answer is negative, which is not possible for time. To avoid this issue, we can simply take the absolute value of the change in time, which would give us a positive value of 0.008 seconds. Alternatively, we can use the magnitude of the change in flux (10 mWB - 20 mWB = 10 mWB) instead of the actual values, which would also result in a positive value of 0.008 seconds.

In summary, the time over which the flux changes is 0.008 seconds, and we can either take the absolute value or use the magnitude of the change in flux to avoid the issue of a negative time.