A coil of resistance 10Ω and inductance 140mH is connected in parallel with a 260Ωresistor across a 230V, 50Hz supply. Calculate the following(i) Current in the coil and phase angle of this current (4 Marks)(ii) Supply current (4 Marks)(iii) Circuit impedance (3 Marks)(iv) Power factor (3 Marks)(v) Power consumed
Question
A coil of resistance 10Ω and inductance 140mH is connected in parallel with a 260Ωresistor across a 230V, 50Hz supply. Calculate the following(i) Current in the coil and phase angle of this current (4 Marks)(ii) Supply current (4 Marks)(iii) Circuit impedance (3 Marks)(iv) Power factor (3 Marks)(v) Power consumed
Solution
(i) Current in the coil and phase angle of this current:
First, we need to calculate the inductive reactance (XL) of the coil. The formula for inductive reactance is XL = 2πfL, where f is the frequency and L is the inductance.
XL = 2π * 50Hz * 140mH = 2π * 50 * 0.14 = 44Ω
The coil is a combination of resistance (R) and inductive reactance (XL), so we can use Pythagoras' theorem to find the total impedance (Z) of the coil.
Z = √(R² + XL²) = √(10² + 44²) = √1936 = 44Ω
The current in the coil (I) can be found using Ohm's law, I = V/Z, where V is the voltage.
I = 230V / 44Ω = 5.23A
The phase angle (φ) can be found using the formula φ = arctan(XL/R).
φ = arctan(44/10) = 77.47°
(ii) Supply current:
The supply current is the same as the current in the coil, as they are connected in parallel. So, the supply current is 5.23A.
(iii) Circuit impedance:
The total circuit impedance (ZT) can be found using the formula for parallel resistances, 1/ZT = 1/Z1 + 1/Z2.
1/ZT = 1/44Ω + 1/260Ω = 0.0227 + 0.00385 = 0.02655
ZT = 1 / 0.02655 = 37.7Ω
(iv) Power factor:
The power factor (PF) can be found using the formula PF = cos(φ).
PF = cos(77.47°) = 0.22
(v) Power consumed:
The power consumed (P) can be found using the formula P = IVcos(φ), where I is the current, V is the voltage, and φ is the phase angle.
P = 5.23A * 230V * 0.22 = 264.9W
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