Free · Physics models
Average Coil EMF from a Flux Change
Find signed average induced voltage for a coil undergoing a uniform perpendicular flux change.
- Formula & worked example
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Calculator inputs
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How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
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Formula and method
A 100 cm² coil with 50 turns and a 0.2 T flux-density increase over 0.1 s has average EMF −1 V.
ΔΦ = ΔB A; average EMF = −N ΔΦ/Δt.
Worked example
Enter these known values and leave the other values blank.
- Coil cross-sectional area
- 100 cm²
- Number of turns in the coil
- 50 turns
- Magnetic flux-density change ΔB
- 0.2 T
- Time
- 0.1 sec
- Flux change per turn ΔΦ
- 0.002 Wb
- Signed average induced EMF
- -1 V
Assumptions and limitations
- Treat the magnetic-field and flux inputs as signed changes over the stated time, rather than static field values. The coil area is fixed and perpendicular to the field change.
- The result is average EMF over the interval. It is instantaneous only when the flux-change rate is constant.
- The minus sign expresses opposition to increasing flux under the chosen coil orientation. Time and area are positive; turns must be a positive integer.
- Enter known quantities and leave the unknown blank. Editable quantities support inverse solutions and locks; inconsistent locked quantities are reported. Unit selectors convert the quantity independently of its display.
- Reviewed hash-pinned model correction: Treat the magnetic-field and flux inputs as signed changes over the stated time, rather than static field values. The coil area is fixed and perpendicular to the field change. The result is average EMF over the interval. It is instantaneous only when the flux-change rate is constant. The minus sign expresses opposition to increasing flux under the chosen coil orientation. Time and area are positive; turns must be a positive integer. Enter known quantities and leave the unknown blank. Editable quantities support inverse solutions and locks; inconsistent locked quantities are reported. Unit selectors convert the quantity independently of its display.
Common questions
Why can the voltage be negative?
The sign follows the chosen coil orientation and the opposition of induced EMF to the signed flux change.
Does a static magnetic field induce EMF?
A static field and fixed coil produce no flux change. The field control here represents a change over the specified interval.
How do I use the inverse calculation?
Clear the quantity you want to find and enter the remaining known values in their selected units. The model can only solve branches with enough independent information.
References
Enforce the documented finite physical branch and inverse domains.