CIRCUITS

Electronics

Current

Current Electricity

Current electricity is a movement of charge, This is almost always the movement of electrons (-)

First, a chemical reaction takes place inside of a cell.

This causes a mild push on electrons caused by an excess number of electrons

The strength of this push is called voltage

Battery is short for battery cells

A typical battery cell is 1.5 Volts

To make a 9V battery, you need 6 cells, each producing 1.5 V of potential all attached in a series

Battery

National Geographic Battery Video

With your group:List as many devices as you can that use batteries!!

Battery Video

Common Power Sources

The voltage for any electric circuit can come from many different sources. Some common examples are: batteries, power plants, fuel cells.

Terminals

•Two ends of the battery are called Terminals• A positive terminal and a negative terminal

•When one terminal of a battery is connected with a conductor to the other terminal of a battery, a circuit results.

Direction of Flow

So, which way does the current flow in a battery?

Positive to Negative?

It started when Ben Franklin first guessed that something flowed through conductors to cause an electrical current

He thought whatever flowed, moved from where there was a lot (or positive) to where there was less (or negative)

Thus, he defined the flow as positive to negative

Negative to Positive?

It was not until after 1897, when English physicist J.J. Thomson discovered the electron that thinking started to change

When the atom parts were discovered and labeled, scientists labeled the parts and charges: protons (+) and electrons (-), but completely separate from Ben Franklin’s ideas

This created confusion, when in fact, physicists realized it was the excess electrons that moved through a circuit, causing current

Negative to Positive!!

So, today, electrical engineers still in fact talk about potential moving from positive to negative

However, physicists, refer to electrons or charges moving from negative to positive

Because the electrons are what actually flows in a current, we will refer to the flow moving from negative to positive

Current

A "flow" of marbles must be sustained in a never-ending looped pathway for electrons. If we take a wire, or many wires joined end-to-end, and loop it around so that it forms a continuous pathway.

A circuit is a pathway of conductive material that allows electrons to flow through continuously without beginning or end.

Circuit

Any break, Anywhere

If a circuit is "broken," that means its conductive elements no longer form a complete path, and continuous electron flow cannot occur in it.

Any break, Anywhere in a circuit prevents electron flow throughout the circuit.

http://www.allaboutcircuits.com/vol_1/chpt_1/3.html

Electric circuitsThe bulb will only light if there is a battery

and a complete circuitWe usually add in a switch to the circuit, so

that we can break the circuit and stop the electric current when we want to.

Current

Current is a measure of how much electric charge flows through a circuit. The more charge that flows, the bigger the current.

Current is measured in units called amps. The symbol for amps is A. For example, 20A is a bigger current than 5A.

Measuring currentA device called an ammeter is used to measure current. Some types of ammeter have a pointer on a dial, but

most have a digital readout. To measure the current flowing through a component in a circuit, you must connect the ammeter in series with it.

What makes a circuit

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Schematics

2 /9 /11

SchoolHouse RockElectricity,

Electricity!

http://www.youtube.com/watch?v=3RzN7T5xpVc

We use circuit symbols to draw diagrams of electrical circuits, with straight lines to show the wires. The diagram shows some common circuit symbols.

Notice the difference between the symbol for a cell and the symbol for a battery? The battery is made from joining cell symbols together.

Circuit Diagrams

The idea of a circuit diagram is to use circuit symbols instead of drawing each component in the circuit. Always try to make the wires straight lines, and don't be tempted to make them wiggly.

The whole point is to make it easier to see what is connected to what. Here you can see how the symbols for a cell (not a battery!) and a lamp look in a circuit diagram.

If you have to draw a circuit diagram from scratch, it is usually easier to draw the circuit symbols first, and then add all the wires. If you have to draw wires to join circuit symbols that are already shown, use a ruler and don't let the wires cross each other.

If instead of a wire you put something like a light bulb in the path of the flow of electrons, you can change the electric energy into another form of energy

First challenge: Get electricity to light a lamp.

Click icon to add picture

The lamp will light when one wire is connected to one battery terminal and the other wire is connected to the other terminal.

There is only one way to connect it to a battery to produce results.

Two or more lamps, however present a new set of challenges.

Circuits consisting of just one battery and one load resistance are very simple to analyze, but they are not often found in practical applications. Usually, we find circuits where more than two components are connected together.

There are two basic ways in which to connect more than two circuit components: series and parallel.

2/10 /11

Series Circuits

Explanations of Ideas

http://lgfl.skoool.co.uk/content/keystage3/Physics/pc/learningsteps/SPCLC/launch.html

Series Circuit

In a television series, you get several episodes, one after the other just like a series circuit.

In a series circuit, all components are connected end-to-end, forming a single path for electrons to flo.

Series Circuits

If you put more lamps into a series circuit, the lamps will be dimmer than before.

In a series circuit, if a lamp breaks or a component is disconnected, the circuit is broken and all the components stop working.

Series circuits are useful if you want a warning that one of the components in the circuit has failed. They also use less wiring than parallel circuits.

Simple Circuit

Current in a Simple Circuit -- Current is defined as the flow of electricity through a circuit over time. This Formula Solver! Series program shows the step-by-step solution for finding current, charge, or time from the other two values (which you can enter yourself).

Power in a Simple Circuit -- In the world of electricity, power is the product of current and voltage. This Formula Solver! Series program shows the step-by-step solution for finding power, current, or voltage from the other two values (which you can enter yourself).

Resistance in a Series Circuit -- This Formula Solver! Series program shows the step-by-step solution for finding resistance in a series circuit (using up to four resistance values which you can enter yourself).

2/15 /11

Parallel Circuit

Two Categories

A parallel circuit is one of the two basic types of electric circuit that can be found in electrical devices.

In a parallel circuit, however, there are multiple pathways between the circuit’s beginning and end.

As a result, since the current has more than one route to take, the circuit can still function if one path fails.

This makes parallel circuits much more fail-resistant than series circuits which is why parallel circuits are common in everyday applications, such as household wiring.

Regardless of how many different paths the circuit has, the total voltage stays the same, and all components of the circuit share the same common points.

A. This set of common points:1. One thing to consider

about parallel circuits is the current load that they carry.

2. When a circuit has multiple paths for current, the circuit's total effective resistance drops.

1. Voltage does not change, this means the current has to increase. (Ohm’s law)

2. Thus, the more paths that a circuit has, the greater the current flow across each path will effectively become.

3. This can lead to damage to the circuit or external equipment, which is why excessive use of outlet extenders or multi-plug inserts is considered hazardous. Parallel circuits are found in virtually all complex electrical devices. Many devices use both series and parallel circuits in conjoined and stand-alone configurations.

Measuring Parallel Circuits

Another aspect of parallel circuits to keep in mind is that such circuits must be measured differently than series circuits.

1. For example, when testing a parallel circuit using a voltmeter or multimeter, which tests multiple measurements, the multimeter must be connected in parallel to properly measure the voltage.

2. Multiple branches means the load is distributed over more than one path, and measuring only one path will not present the full picture.

3. If this isn’t done correctly, the measurement will be faulty, and the circuit may incorrectly be judged defective.

Parallel Circuits

In parallel circuits different components are connected on different branches of the wire. If you follow the circuit diagram from one side of the cell to the other, you can only pass through all the different components if you follow all the branches.

In a parallel circuit, if a lamp breaks or a component is disconnected from one parallel wire, the components on different branches keep working. And, unlike a series circuit, the lamps stay bright if you add more lamps in parallel.

Parallel circuits are useful if you want everything to work, even if one component has failed. This is why our homes are wired up with parallel circuits.

Parallel Circuits Day 2

In a parallel circuit, all components are connected across each other, forming exactly two sets of electrically common points.

A "branch" in a parallel circuit is a path for electric current formed by one of the load components (such as a resistor).

A third lamp placed in parallel with the first two will have its own pathway, too, so it will glow as brightly as the other two.

And each additional bulb will glow brightly until the total burden exceeds the ability of the chemical reaction to deliver electrons fast enough to supply the needs of all of the lamps

Parallel CircuitsTwo or more electrical devices in a circuit

can be connected by series connections or by parallel connections.

When all the devices are connected using parallel connections, the circuit is referred to as a parallel circuit.

In a parallel circuit, each device is placed in its own separate branch.

The presence of branch lines means that there are multiple pathways by which charge can traverse the external circuit.

Each charge passing through the loop of the external circuit will pass through a single resistor present in a single branch.

When arriving at the branching location or node, a charge makes a choice as to which branch to travel through on its journey back to the low potential terminal.

Tollway AnalogyA tollbooth is the main location of resistance

to car flow on a tollway. Adding additional tollbooths within their own

branch on a tollway will provide more pathways for cars to flow through the toll station.

These additional tollbooths will decrease the overall resistance to car flow and increase the rate at which they flow.

As the total current exits the negative (-) battery terminal and travels through the circuit, some of the flow splits off .

Like a river branching into several smaller streams, the combined flow rates of all streams must equal the flow rate of the whole river.

The same thing is encountered where the currents through to the flow back to the positive terminal of the battery (+)

This is the second principle of parallel circuits: the total circuit current is equal to the sum of the individual branch currents.

Finally, applying Ohm's Law to the rightmost ("Total") column, we can calculate the total circuit resistance

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.

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 of each "branch" or path is the same as the potential rise 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. ).

Review

Can you: Define a parallel circuit and explain how it compares to a

series circuit. Construct a parallel circuit. Explain what a voltmeter does and how it is different from

an ammeter.Like the series circuit, parallel circuits also contain

a voltage (current) source as well as wires and other components. The main difference between a series circuit and a parallel circuit is in the way the components are connected. In a parallel circuit the electricity has several paths that it can travel.

More Information

Parallel Circuit

Current in a Parallel Circuit -- Current is a function of voltage and resistance. This Formula Solver! Series program shows the step-by-step solution for finding current in parallel circuits using your own voltage and resistance values.

Power in a Parallel Circuit -- In parallel circuits, power is a function of current and voltage. This Formula Solver! Series program shows the step-by-step solution for using voltage and resistance to find current and power (all with your own values).

Resistance in a Parallel Circuit -- This Formula Solver! Series program shows the step-by-step solution for finding electrical resistance in parallel circuits (using up to four resistance values which you can enter yourself).

http://www.bbc.co.uk/schools/ks3bitesize/science/energy_electricity_forces/electric_current_voltage/revise5.shtml

Voltage Voltage is a measure of the difference in electrical energy between two

parts of a circuit. The bigger the difference in energy, the bigger the voltage.

Voltage is measured in volts. The symbol for volts is V. For example, 230V is a bigger voltage than 12V.

Measuring voltage Voltage is measured using a voltmeter. Some types of voltmeter have a

pointer on a dial, but most have a digital readout. To measure the voltage across a component in a circuit, you must connect the voltmeter in parallel with it.

Using a voltmeter to measure the voltage across a lamp You can measure the voltage across a cell or battery. The more cells, the

bigger the voltage. The more cells, the bigger the voltage

Ohm’s Law

Ohms Law

Ohm's Law defines the relationships between (P) power, (V) voltage, (I) current, and (R) resistance.

One ohm is the resistance value through which one volt will maintain a current of one ampere. 

( I ) Current is what flows on a wire or conductor like water flowing down a river. Current flows from negative to positive on the surface of a conductor. Current is measured in (A) amperes or amps. 

( V ) Voltage is the difference in electrical potential between two points in a circuit. It's the push or pressure behind current flow through a circuit, and is measured in (V) volts. 

( R ) Resistance determines how much current will flow through a component. Resistors are used to control voltage and current levels. A very high resistance allows a small amount of current to flow. A very low resistance allows a large amount of current to flow. Resistance is measured in  ohms. 

( P ) Power is the amount of current times the voltage level at a given point measured in wattage or watts.

Short Circuit

You can incorporate a switch into your circuit to turn a lamp on and off

When the switch is closed, the current flows and the lamp glows.

But if you create a circuit where the lamp glows until they close the switch, at which time the lamp goes out.

This is called short circuiting.

Electrons will travel on the path with the least resistance.

A short circuit is a low-resistance pathway from one terminal of a battery to the other.

Almost all the electric current will flow through the short circuit, and the intended receiver (a lamp in this case) will not operate.

Short circuits often cause a lot of heat. 

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A short circuit may be in a direct- or alternating-current (DC or AC) circuit. If it is a battery that is shorted, the battery will be discharged very quickly and will heat up due to the high current flow. 

Short circuits can produce very high temperatures due to the high power dissipation in the circuit.

If a charged, high-voltage capacitor is short circuited by a thin wire, the resulting huge current and power dissipation will cause the wire to actually explode.