Friday, 4 January 2013

The Series Circuit

http://www.regentsprep.org/regents/physics/phys03/bsercir/default.htm

The 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.
Below is 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 this animation you should notice the following things:

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.

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.

The Parallel Circuit

http://www.regentsprep.org/regents/physics/phys03/bparcir/default.htm
The Parallel 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.
Below is an animation of 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 this animation you should notice the following things:

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 of each branch equals 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 eitherpartial values or with total values but you can not mix parts and totals.

Types of electronic circuits

http://electroniccircuitsforbeginners.blogspot.in/2009/04/types-of-circuits.html
Types of circuits

From the smallest circuit to the largest electronics project, every circuit that performs a useful function has one or more of the same building blocks. I’m not talking about electronic components; I’m talking about sub-circuits that have a defined function.

These circuits are divided in digital and analog. In these pages you’ll learn how to design every type of circuit listed, with emphasis on a functionality level, instead of a component level, in order to be able to create any kind of amplifier as required by the project. Here’s the list of them:

Analog

Amplifiers
Filters
Power sources
Oscillators
Rectifiers
Timers
Modulators
Demodulators

Digital

Logic gates
Counters
Encoders
Decoders
Flip-Flops
Multiplexers
Demultiplexers
Analog to Digital Converter (ADC)
Digital to Analog Converter (DAC)
Microcontrollers
Microprocessors

All of these sub-circuits have a defined function within a complete project, and some of them are even a project on their own. These categories are somewhat broad; every one of them has many different designs and implementations depending on the particular characteristics of the project, for example amplifiers.

There are transistor and OpAmp amplifiers. In transistor amplifiers there are common source, common base, common collector, there are Darlington amplifiers. Transistor amplifiers are further divided by the kind of transistor used: BJT, N-channel JFET, P-channel JFET, MosFET, Nmos, Pmos, Cmos; Each with its own set of configurations.

On OpAmp there are negative feedback, positive feedback, voltage follower and others.

As you can see there are a million different combinations of amplifier topologies as they are called, way too many to be familiar with all of them.

Galvanometer

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/galvan.html

Galvanometer

Galvanometer is the historical name given to a moving coil electric current detector. When a current is passed through a coil in a magnetic field, the coil experiences a torqueproportional to the current. If the coil's movement is opposed by a coil spring, then the amount of deflection of a needle attached to the coil may be proportional to the current passing through the coil. Such "meter movements" were at the heart of the moving coil meters such as voltmeters and ammetersuntil they were largely replaced with solid state meters.

The accuracy of moving coil meters is dependent upon having a uniform and constant magnetic field. The illustration shows one configuration of permanent magnet which was widely used in such meters.

http://www.ncert.nic.in/html/learning_basket/electricity/electricity/effects_of_current/galvanometer.htm

Galvanometer

The torque on a current loop in a uniform magnetic field is used to measure electrical magnetic field is used to measure electrical currents. This current measuring device is called a moving coil galvanometer.

The galvanometer consists of a coil of wire often rectangular, carrying the current to be measured. There are generally many turns in the coil to increase its sensitivity. The coil is placed in a magnetic field such that the lines of B remain nearly parallel to the plane of wire as it turns. This is achieved by having a soft iron cylinder placed at the center of the coil. Magnetic field lines tend to pass through the iron cylinder, producing the field configuration. The moving coil is hung from a spring which winds up as the coil rotates; this winding up produces a restoring torque proportional to the winding up (or twisting) of the spring, i.e. to the angular deflection of the coil. The coil comes to equilibrium when this restoring torque k balances the torque due to the magnetic field balances the torque due to the magnetic field. Since by design field lines are radial,

we have sin q ~ 1, so that for equilibrium

k ø = INBA

NBA

ø = ------ I

Thus the deflection ø of the galvanometer is proportional to the electric current I passing through it
.

Ammeter

http://people.ee.duke.edu/~cec/final/node22.html

Ammeter

An ideal ammeter has zero resistance so that the the circuit in which it has been placed is not disturbed. An ideal ammeter is a short circuit. However, as with the voltmeter, no ammeter can ever be ideal, and therefore all ammeters have some ( hopefully) small internal resistance. To determine the resistance of the ammeter, we will use the circuit in Figure

. According to Ohm's Law, the current in this circuit will be

where

. So the current can be found using the equation:

By using the known quantities

and R, we can solve for the unknown quantity

.
In the procedure that follows it is extremely important that you take precise and accurate measurements. Record each measurement as precisely as the instrument will allow.

Select a 100 resistor. Measure and record its actual value.
Assemble the circuit in Figure . Set the multimeter to the ammeter mode for dc current measurement. Recall this means two things: Place the test leads in the correct banana jacks and press the proper sequence of softkeys.
Use the oscilloscope to measure the voltage across the DC power supply.
Measure the value of the current using the ammeter.
Determine the value of from Equation .

Voltmeter

http://people.ee.duke.edu/~cec/final/node21.html

Voltmeter

An ideal voltmeter has infinite resistance: It is an open circuit. Although it is impossible to make a physical voltmeter with infinite resistance, a well designed voltmeter exhibits a very large internal input resistance. In some experiments, it is important to take into account the finite, non-ideal, internal resistance. To determine the internal resistance of the voltmeter, set up the circuit shown in figure

. The voltmeter reads the voltage across itself, which includes its internal resistance. Since the circuit has only a single branch, the current flowing through the resistor also flows through the voltmeter. The current is given by the equation:

From Ohm's Law, if we know the current (I) and the voltage (

) we can compute

Figure: Circuit for measuring the resistance of the voltmeter.

Select a 1 resistor.
Measure its value using the multimeter.
Set the power supply to provide 10 V (Remember, always measure the voltage provided by the power supply with either the voltmeter or the scope. Do not rely on the digital display on the front panel of the power supply.)
Assemble the circuit in Figure .
Record the voltage measured by the voltmeter
Compute the internal resistance of the voltmeter using Equation .