Ohm’s law
Ohm’s law states that ” DC current flowing through a resistor is directly proportional to the applied voltage. As voltage increase current in line increases, If voltage decreases current in line decreases.”
Such that; V∝I
V=I*R (V=voltage, I=Current, R=Resistance)
‘Resistance‘ is the property of a material. Which is a type of opposition offered by the material to the flow of electrical current. Resistance is the intrinsic property of material which depend upon its overall dimension & materialistic characteristics.
DC power Vs AC power
DC power stay stable at its magnitude. It does not change its direction like the AC power does !
A GIF of pure DC waveform is shown next. Where an electrical load is connected across a battery. When switch get closed, Voltage appear across the load. Parallelly, Current flows through the load.
In a wave GIF below, Both the voltage and current waves move with respect to time. They maintain their respective fixed amplitudes at a stable rate.
AC moves changes its direction with respect to time. AC follows an alternate pattern !
In a wave GIF below. An AC source is connected across the load. When switch get closed, A voltage get appear across the load. Parallelly, Current starts moving through the load.
Both Voltage & current waves are shown on a same plane with their respective magnitude. Both the waves follows the same alternate pattern with a same time of rise & fall. That symmetrical ‘phenomenon’ of voltage & current represents both voltage & current are in phase.
Frequency in AC power
AC wave shown above flows & completes one positive half & one negative half. One positive half & one negative half completes ‘one cycle’.
Frequency shows number of cycles with respect to time. Hz is the unit of frequency. 50 Hz represents 50 cycles per second.
Types of Electrical Loads
There are basically three types of electrical loads :
- Resistor
- Inductor
- Capacitor
- Resistor : Resistor provides resistance to the opposition to the flow of electrical current. Most of the power across resistor get dissipated in a form of heat.
2. Inductor : It is type of coil made from insulated wires. Inductor stores electrical power in a form of magnetic field.
3. Capacitor : Capacitor appears like a sandwich. Dielectric material is sandwiched in between the two conductors. It stores the Electrical in a form of electrostatic charge.
Phase Imbalance
When an Ac supply is applied across pure resistive circuit, Both voltage & current both moves parallelly in phase.
Both inductor & capacitor are type of storage element. Both pushes back their stored power into the circuit. Which results voltage & current parameters of AC power get out of phase.
A GIF of phase imbalance is shown above. Which shows an electrical motor which is a type of inductive load is connected across an ac supply. Voltage appear across the motor when switch get closed.
Voltage waveform is far ahead than current waveform; Almost ahead 90° degree. Which results both voltage & current get out of phase.
This happening due to the stored energy Which produces a type of opposition to current which has generated it. That generated opposition is known as ‘Reactance‘.
Reactance
Reactance is a current opposition property like resistance. Resistance is a readily available value of the circuit. While Reactance is imaginary generated value which generates when AC power supply is get applied across the circuit. Reactance is also having the units ‘ohm‘. Reactance is represented through a symbol ‘X‘.
Pure resistive element do not generates reactance while Inductive circuit & capacitive circuit generates reactance across the circuit.
Reactance from an inductive circuit is called ‘Inductive reactance’. Which is represented through the symbol ‘Xl‘. Inductive reactance ‘Xl’ =2*π*f*L Where; f is frequency, L is inductance
Reactance from a capacitive circuit is called ‘Capacitive reactance’. Which is represented through the circuit ‘Xc‘. Capacitive reactance ‘Xc’= 1/(2*π*f*c) Where; C is capacitance.
Inductive reactance & capacitive reactance are counter to each other. Overall reactance is the subtraction of both the quantities. The resultant reactance type belongs to the reactance whichever is higher.
For example let suppose there is capacitive reactance is 30Ω While inductive reactance is 35Ω. The resultant reactance is Inductive reactance-capacitive reactance; which is 5Ω(Inductive).
If capacitive reactance is 40Ω While inductive reactance is 30Ω. The resultant reactance is Capacitive reactance-Inductive reactance which is 10Ω.
What if there is a circuit which has all the three opposing element Resistance, Inductive reactance & Capacitive reactance ?
Since, Resistance, Inductive reactance & Capacitive reactance all are opposing element Which can be categorized in a single term. & that term is known as ‘Impedance‘.
Impedance= √R²+(Xl-Xc)² or √R²+(Xc-Xl)² Which ever the term is higher Xl or Xc !
Behavior of reactance across DC power
There are two types of reactance; Inductive reactance & capacitive reactance. Both the reactance’s are frequency dependent.
Inductive reactance; 2*π*f*L. When frequency is zero, Inductive reactance also becomes zero. This means at DC supply, inductive reactance is zero. And the inductor behaves like a short element.
Capacitive reactance = 1/(2*π*f*c). When frequency is zero, Capacitive reactance get infinite. Which means at DC supply, Capacitive reactance get infinite & Capacitor behave like an open circuit.
Summary
- Ohm’s law states that the direct current (DC) flowing through a resistor is proportional to the voltage applied. This relationship is described by the formula ‘V=IR‘.
- Resistance opposes current flow and is dictated by material properties.
- DC power remains stable in magnitude, unlike alternating current (AC), which oscillates in direction.
- AC has a frequency measured in hertz, reflecting the number of cycles per second. Electrical loads include resistors, inductors, and capacitors, each with distinct functions.
- Reactance, an opposition in AC circuits due to inductors and capacitors, differs from resistance.
- Overall opposition in circuits is termed impedance, influenced by resistance and reactance.