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Kirchhoff's Current Law

Kirchhoff’s Circuit laws are two approximate equalities that deal with the current and voltage in electrical circuits. These approximations were first described in 1845 by Gustav Kirchhoff [1]. This generalized the work of Georg Ohm and preceded the work of Maxwell. Both of Kirchhoff’s laws can be understood as corollaries of the Maxwell equations in the low-frequency limit. The laws were the first approximations for AC circuits.

Kirchhoff’s current law is often referred to as Kirchhoff’s junction rule or Kirchhoff’s point rule. The principle of conservation of electric charges states that at any junction in an electrical circuit, the sum of currents flowing into the node is equal to the sum of currents flowing out of that node, or the algebraic sum of currents in a network of conductors meeting at a point is zero.

∑ IK = 0

KCL in its usual form is dependent on the assumption that current flows only in conductors and that whenever current flows into one end of a conductor it immediately flows out of the other end. This however is not a safe assumption for AC circuits. It is possibly to salvage the form of KCL by considering “parasitic capacitances” distributed along the conductors. 

[1] Oldham, p.52

Current And Power Dissipation

Circuit is attached (a) Calculate the value of the current through the 12 V battery shown in FIGURE 3. (b) Calculate the power dissipated in R1, R2 and R.

Electronic Principles Questions

1) Figure 1 represents the equivalent circuit of a voltage regulator where an unregulated 12V source is used to provide a stabilised voltage Vout using an 8V zener diode. Using Kirchhoff's voltage law and by writing the appropriate equations find: i. The currents i2 & i3. ii. The output voltage Vout. iii. The power

Communications and Control (Mathematical Model)

1.6 LINEARISATION 1.1 Specify variable x and coefficients a, b and c in the differential equation (1.5) for a) the mass-spring-damper system in Fig 1.1 described by (1.1), and b) the RLC circuit in Fig. 1.2 described by (1.3). 1.2 Let x = uc, where uc is the voltage on the capacitor shown in Fig 1.6. Show that the dyna