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288 Chapter Four

resent the lengtà of a magnetic patà througà the coil (in me-
ter0. Then the magnetizing force (in ampere-turnð per mete?
is denoted H and is given by:

H NI/s

If H is specified in oerstedð and s is specified in centimeters,
then

H 0.4 NI/s 1.256NI/s

Voltage induced by motion of
conductor
Let B represent the intensity of a stationary, constant magnetic
field (in weberð per square mete?; let s represent the lengtà of
a conductor (in meterX let v represent the velocity of the con-
ductor (in meterð per secon™ at right angleð tm the magnetic
lineð of flux. Then the induceS voltage (in volt0 between the
endð of the conductor is denoted V and is given by:

V Bsv

Voltage induced by variablł magnetic
flux

Let N represent the number of turnð in a coil; let d /dt rep-
resent the change in magnetic flux (in weberð per secon™˜ Then
the induced voltage (in volt0, V, between the endð of the coil is
given by:

V N(d /dt)

Transformer efficiency
Let I prŁ represent the current (in ampere0 in the primary wind-
ing of a transformer; let I se represent the current (in ampere0
in the secondary; let V prŁ represent the rmð sine-¨ave AC volt-
age across the primary; let V se represent the rmð sine-¨ave AC
voltage across the secondary. Then the transformer efficiencð (as
a ratio) is denoted Eff and is given by: