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- 1. Elektronika<br />AgusSetyo Budi, Dr. M.Sc<br />Sesion #12<br />JurusanFisika<br />FakultasMatematikadanIlmuPengetahuanAlam<br />
- 2. Outline <br />20-1: How XL Reduces the Amount of I<br />20-2: XL = 2πfL<br />20-3: Series or Parallel Inductive Reactances<br />20-4: Ohm's Law Applied to XL<br />20-5: Applications of XLfor Different Frequencies<br />20-6: Waveshape of vLInduced by Sine-Wave Current<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />2<br />07/01/2011<br />
- 3. Inductive Reactance<br />07/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />3<br />
- 4. 20-1: How XL Reduces the Amount of I<br />An inductance can have appreciable XL in ac circuits to reduce the amount of current. <br />The higher the frequency of ac, and the greater the L, the higher the XL.<br />There is no XL for steady direct current. In this case, the coil is a resistance equal to the resistance of the wire.<br />07/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />4<br />
- 5. 20-1: How XL Reduces the Amount of I<br /><ul><li>In Fig. 20-1 (a), there is no inductance, and the ac voltage source causes the bulb to light with full brilliance.
- 6. In Fig. 20-1 (b), a coil is connected in series with the bulb.
- 7. The coil has a negligible dc resistance of 1 Ω, but a reactance of 1000 Ω.
- 8. Now, I is 120 V / 1000 Ω, approximately 0.12 A. This is not enough to light the bulb.
- 9. In Fig. 20-1 (c), the coil is also in series with the bulb, but the battery voltage produces a steady dc.
- 10. Without any current variations, there is no XLand the bulb lights with full brilliance.</li></ul>07/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />5<br />
- 11. 20-2: XL = 2πfL<br />The formula XL = 2πfL includes the effects of frequency and inductance for calculating the inductive reactance.<br />The frequency is in hertz, and L is in henrys for an XL in ohms.<br />The constant factor 2π is always 2 x 3.14 = 6.28.<br />The frequency f is a time element.<br />The inductance L indicates the physical factors of the coil.<br />Inductive reactance XL is in ohms, corresponding to a VL/IL ratio for sine-wave ac circuits.<br />07/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />6<br />
- 12. 20-3: Series or Parallel Inductive Reactances<br /><ul><li>Since reactance is an opposition in ohms, the values XL in series or in parallel are combined the same way as ohms of resistance.
- 13. With series reactances, the total is the sum of the individual values as shown in Fig. 20-5 (a).
- 14. The combined reactance of parallel reactances is calculated by the reciprocal formula.</li></ul>Fig. 20-5<br />07/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />7<br />
- 15. 20-4: Ohm's Law Applied to XL<br />The amount of current in an ac circuit with only inductive reactance is equal to the applied voltage divided by XL.<br />I = V/XL = 1 A<br />I = V/XLT = 0.5 A<br />I1 = V/XL1 = 1 A<br />I2 = V/XL2 = 1 A<br />IT = I1 + I2 = 2 A<br />Fig. 20-6: <br />07/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />8<br />
- 16. 20-5: Applications of XLfor Different Frequencies<br />The general use of inductance is to provide minimum reactance for relatively low frequencies but more for higher frequencies.<br />If 1000 Ω is taken as a suitable value of XL for many applications, typical inductances can be calculated for different frequencies. Some are as follows:<br />2.65 H 60 Hz Power-line frequency<br />160 mH 10,000 Hz Medium audio frequency<br />16 mH 10,000 Hz High audio frequency<br />1.6 μH 100 MHz In FM broadcast band <br />07/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />9<br />
- 17. 20-6: Waveshape of vLInduced by Sine-Wave Current<br />Induced voltage depends on rate of change of current rather than on the absolute value if i.<br />A vL curve that is 90° out of phase is a cosine wave of voltage for the sine wave of current iL.<br />The frequency of VL is 1/T.<br />The ratio of vL/iL specifies the inductive reactance in ohms.<br />07/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />10<br />
- 18. 20-6: Waveshape of vLInduced by Sine-Wave Current<br />di/dt<br />di/dt for Sinusoidal Current is a Cosine Wave <br />di<br />L<br />vL =<br />dt<br />0<br /><br />Current<br />Sinusoidal Current<br />Iinst. = Imax× cos <br />07/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />11<br />
- 19. 20-6: Waveshape of vLInduced by Sine-Wave Current<br />V<br />Amplitude<br />0<br />Time<br />Θ = -90<br />I<br />V<br />I<br />Inductor Voltage and Current<br />07/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />12<br />
- 20. 20-6: Waveshape of vLInduced by Sine-Wave Current<br />Application of the 90° phase angle in a circuit<br />The phase angle of 90° between VL and I will always apply for any L with sine wave current.<br />The specific comparison is only between the induced voltage across any one coil and the current flowing in its turns.<br />07/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />13<br />
- 21. 20-6: Waveshape of vLInduced by Sine-Wave Current<br /><ul><li> Current I1 lags VL1 by 90°.
- 22. Current I2 lags VL2 by 90°.
- 23. Current I3 lags VL3 by 90°.</li></ul>NOTE: I3 is also IT for the series-parallel circuit.<br />Fig. 20-8<br />07/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />14<br />
- 24. 07/01/2011<br />© 2010 Universitas Negeri Jakarta | www.unj.ac.id |<br />15<br />TerimaKasih<br />

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