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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?

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Class 12 Physics
CBSE and UP Board
Alternating Current
Chapter-7 Exercise 7.13
Additional Exercise

NCERT Solutions for Class 12 Physics Chapter 7 Question 13

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1 Answer

  1. Inductance of the inductor, L = 0.50 H

    Resistance of the resistor, R = 100Ω.

    Potential of the supply voltage, V = 240 V

    Frequency of the supply, v = 50 Hz

    Ans (a).

    Peak voltage is given as: V0 = √2 V

    = √2 x 240= 339.41 V

    Angular frequency of the supply, ω = 2πν = 2π x 50 = 100π rad/s

    Maximum current in the circuit is given as:

    I0 = V0 /√ (R² + ω² L²) =339.41/√[ (100)² + (100π)² (0.50)²

    =1.82 A

    Ans (b).

    Equation for voltage is given as : V= V0 cosωt

    Equation for current is given as ;I = Icos(ωt-φ )

    Where,φ = Phase difference between voltage and current .At time t=0

    V= V0(voltage is maximum)

    Hence, the time lag between maximum voltage and maximum current is φ/ω

    Now, phase angle φ is given by the relation,

    tan φ = ωL/R

    =(2π x 50 x 0.5)/100=1.57

    =>φ= 57.5º = 57.5 π/180 rad

    =>ωt =57.5 π/180

    =>t = 57.5 /(180 x 2π x50)= 3.19 x 10⁻³ s = 3.2ms

    Hence ,the time lag between maximum voltage and maximum current is 3.2 ms

     

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