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NCERT Class XII Chapter
Alternating Current
Questions With Solutions

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Question : 13
Total: 26
A coil of inductance 0.50 H and resistance 100 Ω is connected to a 240 V. 50 Hz ac supply.
(a) What is the maximum current in the coil?
(b) What is the time lag between the voltage maximum and the current maximum?
Solution:  

Inductive reactance
XL = 2πf L = 2π × 50 × 0.5 = 157 Ω
Impedence Ζ = √R2+XL2 = √(100)2+(157)2
= 186.14 Ω
(a) Virtual current in the coil
Iv =
Ev
Z
 =
240
186.14
 = 1.29 A
Maximum current, I0 = Iv√2 = 1.82 A

(b) Phase lag, tan ϕ =
XL
R
 = 1.57
φ = tan–1 (1.57) = 57.5° or φ = 0.32 π radian
Time lag, t = φ/ω = 3.2 ms
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