Voltage on inductor

I try to calculate voltage spike on inductor after inductor is disconnected from voltage source. You can see my method of computing below, but I thing there is some mistake in method, because the calculated voltage on inductor is IMHO too small. I would expect hundreds of volts. Where is mistake?
Thank you very much.

I can't follow your math, but aren't you making this harder than it actually is? With the switch closed the current in the inductor is nominally 12 A. When the switch is opened, the current wants to remain at 12 amps with a 100 ohm load. E = I*R = 12*100 = 1200 volts

Ylli said:

I can't follow your math, but aren't you making this harder than it actually is? With the switch closed the current in the inductor is nominally 12 A. When the switch is opened, the current wants to remain at 12 amps with a 100 ohm load. E = I*R = 12*100 = 1200 volts

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Sounds good Thank you.