Lecture 3 (Week 3)

1.

Kirchhoff’s Current Law
OEk 1115 - Fundamentals of Electronics
Lecture 3

2.

Outline
Kirchhoff’s Current Law
Current Dividers
Multimeter

3.

Kirchhoff’s Current Law
Kirchhoff’s voltage law deals with voltages in a single closed path.
Kirchhoff’s current law applies to currents in multiple paths.
The sum of the currents into a node (total current in) is equal to the sum of the
currents out of that node (total current out).

4.

Kirchhoff’s Current Law
A node is any point or junction in a circuit where two
or more components are connected.
In a parallel circuit, a node is a point where the
parallel branches come together.

5.

Kirchhoff’s Current Law
By Kirchhoff’s current law, the sum of
the currents into a node must equal the
sum of the currents out of that node.
The algebraic sum of all of the currents
entering and leaving a node is equal to
zero.

6.

Kirchhoff’s Current Law
An illustration of Kirchhoff’s current law.

7.

Kirchhoff’s Current Law
Example. You know the branch currents in the circuit. Determine the total current
entering node A and the total current leaving node B.

8.

Kirchhoff’s Current Law
Example. Determine the current through R2.

9.

Kirchhoff’s Current Law
Example. Use Kirchhoff’s current law to find the current measured by ammeters
A3 and A5.

10.

Kirchhoff’s Current Law
Solution.

11.

Current Dividers
A parallel circuit acts as a current divider because the current entering the
junction of parallel branches “divides” up into several individual branch currents.
The total current divides among parallel resistors into currents with values
inversely proportional to the resistance values

12.

Current Dividers
The current (Ix) through any branch equals the total parallel resistance (RT)
divided by the resistance (Rx) of that branch, and then multiplied by the total
current (IT) into the junction of parallel branches.

13.

Current Dividers
Example. Determine the current through each resistor in the circuit.

14.

Current Dividers
Current-Divider Formulas for Two Branches.

15.

Current Dividers
Example.

16.

Power in Parallel Circuits
Total power in a parallel circuit is found by adding up the powers of all the
individual resistors, the same as for series circuits.

17.

Power in Parallel Circuits
Example. Determine the total amount of power in the parallel circuit.

18.

Power in Parallel Circuits
Example. The amplifier in one channel of a stereo system drives two parallel
speakers. If the maximum voltage to the speakers is 15 V, how much power must
the amplifier be able to deliver to the speakers?

19.

How to use a Multimeter?
A multimeter is a measuring instrument that we will use frequently throughout
electrical experiments.
A Multimeter is an electronic instrument, every electronic technician and
engineers widely used piece of test equipment.
A multimeter is mainly used to measure the three basic electrical characteristics
of voltage, current, and resistance. It can also be used to test continuity between
two points in an electrical circuit.

20.

Digital Multimeter
We mostly used multimeter is a digital multimeter (DMM).
The DMM performs all functions from AC to DC other than
analog.
It has two probes positive and negative indicated with black
and red color is shown in the figure.
Advantages of a Digital Multimeter are its output display
which directly shows the measured value, high accuracy,
ability to read both positive and negative values.

21.

Analog Multimeter
The Analog Multimeter or VOM (Volt-Ohm-Milliammeter) is
constructed using a moving coil meter and a pointer to
indicate the reading on the scale.
Advantages of an Analog Multimeter are that it is
inexpensive, doesn’t require a battery, can measure
fluctuations in the readings.

22.

Direct Current vs Alternating Current
Direct current (abbreviated DC) is current that always flows in one direction.
Direct current is supplied by everyday batteries—like AA and AAA batteries—or the
one in your cell phone.
Alternating current (abbreviated AC) is current that changes direction, usually
many times in one second. The wall outlets in your house provide alternating
current that switches directions 60 times per second.
Warning: Do not use a multimeter to measure the wall outlets in your home.

23.

How to measure voltage?

24.

How to measure current?

25.

How to measure resistance?

26.

How to do a continuity check?

27.

Tinkercad.com

28.

Q&A
Any Questions?