Figure 8
A coil having a resistance of 422 and a constant inductance of 2 H is switched across a 20 V d.c. supply. [4]
Calculate (a) time constant (b) the final value of current
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ε is ϕ ahead of i
because i and R is in phase and i.e., −Z and ε are in phase as ε=ε0sinwt
from diagram
i=−Zε0sin(ωt−ϕ)
where, ϕ=tan−1RXL
b) i=1.0A (given)
VR=160V=iR⇒R=1160=160
VL=120V=iXL⇒XL=1120=120
Vnet=VR2+VL2
=(160)2+(120)2
=25600+14400
=200 : effective value of apphed voltage
Z=
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