kirohhoffs laws!can you explain?

Question

also please tell me the things you know about internal resistance and electric resistance.

Answer 1

Kirchhoff's Rules:

1. The Voltage Rule (AKA the Loop Rule):

The total voltage in a loop of a circuit is zero.

For example, you have a figure-8 circuit (in a digital clock). You have a total of 3 loops. (the top loop, the bottom loop, and the loop made by the outside wires, forgetting the middle line). The total voltage in each loop is 0.

2. The Current Rule (AKA the Junction Rule)
The current flowing though a junction is equal to the amount of current flowing out.

Example, if you have a Y-shaped assembly, where one wire carries current to the other 2. The other 2 wires would carry different amounts of curent compared to the 1st, but the total current in wires 2 and 3 is the same as the current in wire 1

Internal resistance- The resistance that is present in the electrical source. All batteries and generator have this.

Electric resistance- the formal name of the resistance through a resistor

Answer 2

Kirkhoffs laws simply state two fairly obvious facts.

The first is that the number of electrons flowing into a circuit equals the number that flow out. Ie electrons cannot be created or destroyed in the circuit.

The second is that if an electron goes all the way round a circuit back to its starting point, it will have the same energy. Ie energy cannot be created or destroyed.

An electrical resistance is simply something that causes flowing electrons to lose energy - usually by heating the resistor.

Internal resistance is a fictitious resistance. It is the most confusing of the questions you asked.

If you think of a battery, it should give the same voltage regardless of how much current flows. Now R = dV/dI - generalising Ohms law so that it is the slope of the V/I curve. So a perfect battery has dV=0 so resistance zero. In fact, any real battery will show a small drop in voltage as you draw more current, so dV/dI is not zero. This is usually expressed as an internal resistance of the battery, but this is a convenience. You should not think of the battery as having a resistance in the normal sense, and usually this internal resistance will vary with current.

Answer 3

Kirchhoff's laws

Most of the circuit problems we encounter can be solved by repeatedly applying the rules for adding resistors in series or parallel, until the problem has been reduced to one of a battery connected to a single resistor.

But to solve more complex circuit problems, such as those with more than one battery, it is sometimes necessary instead to write equations based on Kirchhoff's Laws, which are formal mathematical statements of two physical facts.

Kirchhoff's law #1 states that the voltage changes around a closed path in a circuit add up to zero, where the voltage change DV = emf in going through a battery from - terminal to + terminal is considered to be positive, and the voltage change DV = I R in going through a resistor in the assumed direction of the current I is considered to be negative.


Kirchhoff's law #2 states that the sum of the currents entering any node (i.e., any junction of wires) equals the sum of the currents leaving that node.

The first law just restates what you already know about electrical potential: every point in a circuit has a unique value of the potential, so travelling around the circuit by any path must bring you back to the potential you started from. Using the analogy to elevation, if you hike from any starting point in the mountains and wander around by any choice of paths but finish at your original starting point, the sum of the elevation changes along your path will add up to zero.

The second law just restates the fact that electric charge is conserved: electrons or protons are not being created or destroyed in the node (or if they are, anti-particles with the opposite charge are being created or destroyed along with them) so in any given time interval, the charge that enters is equal to the charge the leaves. The node is assumed to have negligible capacitance, so charge cannot just build up there.