ELECTRICAL THEORY AND ITS APPLICATION IN REAL SYSTEM
In Malaysia technology university UTM, every singles student who take the circuit theory course (SKEE 1023) have to learn this course in their first semester. By this course student will exposed to basic law, theorem and methods of laws such as Norton theorem and Thevenin’s theorem, concept of series and parallel circuits and etc. Based on these, student will be able to apply the knowledge when doing the experiment in the laboratory. In the circuit theory class, the students will able to solve the problem based on theoretical while in laboratory student facing the real problem that may different to theoretical learning. This course also help student to strengthen their basic knowledge in electrical engineering because all of this theorem and law will be used when they in semester 2 and above.
VOLTAGE
Voltage is a measure of the energy carried by the charge. Strictly: voltage is the "energy per unit charge". The proper name for voltage is potential difference or p.d. for short, but this term is rarely used in electronics. Voltage is supplied by the battery (or power supply).Voltage is used up in components, but not in wires. We say voltage across a component. Voltage is measured in volts, V. Voltage is measured with a voltmeter, connected in parallel. The symbol V is used for voltage in equations.
Voltage at a point and 0V (zero volts)
Voltage is a difference between two points, but in electronics we often refer to voltage at a point meaning the voltage difference between that point and a reference point of 0V (zero volts).Zero volts could be any point in the circuit, but to be consistent it is normally the negative terminal of the battery or power supply. You will often see circuit diagrams label with 0V as a reminder. We may find it helpful to think of voltage like height in geography. The reference point of zero height is the mean (average) sea level and all heights are measured from that point. The zero volts in an electronic circuit is like the mean sea level in geography.
Zero volts for circuits with a dual supply
Some circuits require a dual supply with three supply connections as shown in the diagram. For these circuits the zero volts reference point is the middle terminal between the two parts of the supply. On complex circuit diagrams using a dual supply the earth symbol is often used to indicate a connection to 0V, this helps to reduce the number of wires drawn on the diagram. The diagram shows a ±9V dual supply, the positive terminal is +9V, the negative terminal is -9V and the middle terminal is 0V.
Voltage is the cause, current is the effect is a statement which can be defined as voltage attempts to make a current flow, and current will flow if the circuit is complete. Voltage is sometimes described as the 'push' or 'force' of the electricity, it isn't really a force but this may help us to imagine what is happening. It is possible to have voltage without current, but current cannot flow without voltage.
SERIES CIRCUIT
A series circuit has more than one resistor (anything that uses electricity to do work) and gets its name from only having one path for the charges to move along. Charges must move in "series" first going to one resistor then the next. If one of the items in the circuit is broken then no charge will move through the circuit because there is only one path. There is no alternative route. Old style electric holiday lights were often wired in series. If one bulb burned out, the whole string of lights went off. Can we imagine an animation of a series circuit where electrical energy is shown as gravitational potential energy (GPE). The greater the change in height, the more energy is used or the more work is done. In our imagination we should notice the following thing which is the battery or source is represented by an escalator which raises charges to a higher level of energy. As the charges move through the resistors (represented by the paddle wheels) they do work on the resistor and as a result, they lose electrical energy. The charges do more work (give up more electrical energy) as they pass through the larger resistor. By the time each charge makes it back to the battery, it has lost all the energy given to it by the battery. The total of the potential drops ( - potential difference) across the resistors is the same as the potential rise ( + potential difference) across the battery. This demonstrates that a charge can only do as much work as was done on it by the battery. The charges are positive so this is a representation of Conventional Current (the apparent flow of positive charges) The charges are only flowing in one direction so this would be considered direct current ( D.C. ).
The following rules apply to a series circuit:
- The sum of the potential drops equals the potential rise of the source.
- The current is the same everywhere in the series circuit.
- The total resistance of the circuit (also called effective resistance) is equal to the sum of the individual resistances
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- Ohm's Law may be used in a series circuit as long as you remember that you can use the formula with either partial values or with total values but you can not mix parts and totals.
PARALEL CIRCUIT
A parallel circuit has more than one resistor (anything that uses electricity to do work) and gets its name from having multiple (parallel) paths to move along . Charges can move through any of several paths. If one of the items in the circuit is broken then no charge will move through that path, but other paths will continue to have charges flow through them. Parallel circuits are found in most household electrical wiring. This is done so that lights don't stop working just because you turned your TV off. Try to imagine a parallel circuit where electrical energy is shown as gravitational potential energy (GPE). The greater the change in height, the more energy is used or the more work is done. In our imagination we should notice the following thing which is more current flows through the smaller resistance. (More charges take the easiest path. The battery or source is represented by an escalator which raises charges to a higher level of energy. As the charges move through the resistors (represented by the paddle wheels) they do work on the resistor and as a result, they lose electrical energy. By the time each charge makes it back to the battery, it has lost all the electrical energy given to it by the battery. The total of the potential drops ( - potential difference) of each "branch" or path is the same as the potential rise ( + potential difference) across the battery. This demonstrates that a charge can only do as much work as was done on it by the battery. The charges are positive so this is a representation of conventional current (the apparent flow of positive charges) The charges are only flowing in one direction so this would be considered direct current ( D.C. ).
The following rules apply to a parallel circuit:
- The potential drops in each branch equals to the potential rise of the source.
- The total current is equal to the sum of the currents in the branches.
- The inverse of the total resistance of the circuit (also called effective resistance) is equal to the sum of the inverses of the individual resistances.
One important thing to notice from this last equation is that the more branches you add to a parallel circuit (the more things you plug in) the lower the total resistance becomes. Remember that as the total resistance decreases, the total current increases. So, the more things you plug in, the more current has to flow through the wiring in the wall. That's why plugging too many things in to one electrical outlet can create a real fire hazard.
- Ohm's Law may be used in a parallel circuit as long as you remember that you can use the formula with either partial values or with total values but you can not mix parts and totals.
APPLICATION OF ELECRICAL THEORY