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16 Mar 2010 19:49:18 IST

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1)a coil of inductance 0.5H and resistance 100? is connected to 240V,50 Hz ac supply.what is the pha

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1)a coil of inductance 0.5H and resistance 100Ω is connected to 240V,50 Hz ac supply.what is the phase difference between max voltage and max currenta) 90degreesb) 57 degreesc) 120degreesd) 180 degrees

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Vivek V Bhatnagar

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18 Mar 2010 13:29:53 IST

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the answer is 57.5 degrees.

tan (phi) = (omega x L) / R

where symbols have their usual meanings

aal izz well

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18 Mar 2010 13:43:50 IST

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i thnk its option a) 90 degrees..

Vivek V Bhatnagar

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18 Mar 2010 14:05:28 IST

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omega = 2 x pi x frequency = 100 x pi

L = 0.5

R = 100

Plugging these values in the eqn. we get

tan (phi) = pi / 2

i.e. phi = tan^-1(pi / 2)

use tables or a calculator to get the value of phi as around 57.5 degrees

Aakash Anuj

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18 Mar 2010 17:58:52 IST

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use tan phi = Xc-XL /R here Xc is 0 as there is no capacitoruget 57 .5 degrees

edison

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22 Jun 2011 18:11:26 IST

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Phasor Diagrams

It is sometimes helpful to treat the phase as if it defined a vector in a plane. The usual reference for zero phase is taken to be the positive x-axis and is associated with the resistor since the voltage and current associated with the resistor are in phase. The length of the phasor is proportional to the magnitude of the quantity represented, and its angle represents its phase relative to that of the current through the resistor. The phasor diagram for the RLC series circuit shows the main features.

Note that the phase angle, the difference in phase between the voltage and the current in an AC circuit, is the phase angle associated with the impedance Z of the circuit.

Now in LR circuit

X_C = 0

X_L = w L = 2pi*f L = 2pi * 50 * 0.5 = 50pi

R = 100 ohms

Thus,

phase difference = phi = tan^-1 X_L / R = tan^-1 50 pi / 100

or phi = tan^-1 pi/2 = 57.5 degrees

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