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| http://www.gcsescience.com/pme8.htm |
Friday, 23 May 2014
Electrical Circuits Application
While electrical circuits themselves are used everywhere in our everyday lives, the concepts behind electrical circuits have led to the practical use of safety devices such as circuit breakers. Circuit breakers that are used at the distribution board in houses are called MCB's or miniature circuit breakers. Essentially, breakers limit the current which can flow through a circuit. In a breaker, the heating effect on a bimetallic strip causes it to bend and trip a spring-loaded switch. Typically a single circuit is limited to 20 amperes, although this can vary. When there is a short circuit, which creates a large surge of current, a small electromagnet consisting of wire loops around a piece of iron will pull the strip, separating the contacts and breaking the circuit. After the fault causing the short circuit is repaired, the contacts can be pushed together by lifting a switch on the outside of the circuit breaker.
Electrical Circuits Reflection
This unit was different from the others because we started off with a virtual lab. This virtual lab helped to show us Ohm's Law, which is V=IR with V being voltage (volts), I being current (amps) and R being resistance (ohms). This is the equation we use to solve circuits. The virtual lab helped us see the relationship between the three components. During the lab, we noticed that as the voltage increased, the brightness of the light bulb increased. Alternatively, the current decreased, as the resistance increased. This means that I 
V and I 1/R.
Current is moving electrons, which also means that it can be represented as C/S or coulomb per second. The unit for current is known as an ampere. Increasing the current causes more electricity to move through the device as seen using Ohm's Law. Voltage is electrical potential, as we know from the previous unit. This also refers to how much work a battery in a circuit can do.The unit for voltage can be represented as J/C or joules per unit charge, which is also known as a volt. As current and voltage are directly proportional, the greater the current, the more voltage. Lastly, resistance slows down the current due to collision of electrons with atoms of the material they are passing through, which causes them to lose energy. As the resistance of a circuit increases, the current decreases as seen through the relationship of I 1/R.
There are 2 types of circuits that we studied, series and parallel. Series circuits are connected so that current passes through each element in turn without branching off. For parallel circuits, the current can only flow in one path, therefore the current stays constant throughout the entire circuit. Parallel circuits are a closed circuit in which the current divides into two or more paths before recombining to complete the circuit. Because there is more than one path for the current to flow, the current splits at nodes or junctions, which is any point where the current can split. This also means that each branch is independent from each other, which also means that the voltages across each branch are equal.
We also completed another virtual lab where we learned how the total resistances of circuits changes depending on whether it is a series or parallel circuit. The first thing we noticed in this lab was that when we added an additional lightbulb to our original circuit, the lightbulbs were both dimmer, and the current decreased. For series circuits, the total resistance of the circuit can be found by adding values for all the resistance together. This relationship can be seen as Req (total resistance) = R1+R2... However for circuits in parallel, the relationship between 2 resistance in parallel in relation to the total resistance of the circuit can be shown as 1/Req=1/R1+1/R2.
The next principle we learned to apply to solving circuits were Kirchhoff's Voltage Law and Kirchhoff's Current Law. Kirchhoff's Voltage Law is based on the conservation of energy, where the total amount of energy gained per unit charge (voltage gained) must be equal the amount of energy lost per unit charge (voltage dropped) as both energy and charge are both conserved.
For Kirchhoff's Current Law states that at any node or junction in an electrical circuit, the sum of currents flowing into that node is equal to the sum of the current flowing out of that node. Therefore 
I in = I out.
Using these concepts we are able to solve both series and parallel circuits. For series circuits, we must first find the total resistance of the circuit, which is a concept we learned through the virtual lab by adding the resistances together. With this, we are able to solve for the total current of the circuit if we already know the voltage the battery produced. Since we know that the current stays constant through a series circuit, we can now solve for each voltage drop over each resistance in the circuit by using the total current, and the resistance to solve for V(V=IR). With our knowledge of Kirchhoff's Voltage Law, once we find each individual voltage drop, we know we have correctly solved the circuit by adding each voltage drop together, which should equal the voltage produced by the battery.
For parallel circuits, we can find the total resistance of the circuit by using 1/Req=1/R1+1/R2... to once again find the total current of the circuit. With the total current we can find the voltage drop using V=IR. Once we have found the total current of the circuit and the voltage drop, we can expand backwards to find how the current splits. Since the voltage across each branch is the same, we can solve for I using the individual resistances and the voltage for each branch.
The next concept we learned about was electrical power. As we learned, when a charges flows through a resistor, it loses energy due to collisions with the atoms in the wire. This energy loss is transformed into heat energy and is related to voltage drop since V=PE/q. Because power is the rate of doing work at which energy is transformed, Joules Law states that P=VI. In addition P=I^2R or P=V^2/R. To further extend this, we can also find electrical energy, since E=P(t) where t is time. Since a joule is a very small unit, we can use the kilo Watt-hour to represent energy. With being able to solve parallel and series circuit, we could also solve combination circuits, which combine principle from being able to solve both types of circuits.
The last section of this unit we learned was terminal voltage. Terminal voltage is the voltage (potential) difference between the terminals of a battery when connected to a circuit. This is because the battery contributes to some resistance to a circuit, also known as internal resistance. Where terminal voltage is the actually voltage that goes through the circuit, electromotive force or EMF is the maximum voltage that the battery can produce. When a cell is specifically being charged by another cell, the current flows backward therefore Vt (terminal voltage) = E (EMF) + IR (internal resistance), however when the cell is supplying current to the circuit, Vt = E - IR.
The most difficult part to this unit was just being able to and knowing when to apply each concept. When it came to the point where we were combining solving combination circuits, while having to use electrical power and electrical energy, I found it more difficult to just remember when to apply each concept. However this became easier as we continued doing more practice problems, and I became more used to solving more complicated problems.
V and I 1/R. |
| Shows Ohm's Law (V=IR) http://phet.colorado.edu/en/simulation/circuit-construction-kit-dc |
1/R.There are 2 types of circuits that we studied, series and parallel. Series circuits are connected so that current passes through each element in turn without branching off. For parallel circuits, the current can only flow in one path, therefore the current stays constant throughout the entire circuit. Parallel circuits are a closed circuit in which the current divides into two or more paths before recombining to complete the circuit. Because there is more than one path for the current to flow, the current splits at nodes or junctions, which is any point where the current can split. This also means that each branch is independent from each other, which also means that the voltages across each branch are equal.
We also completed another virtual lab where we learned how the total resistances of circuits changes depending on whether it is a series or parallel circuit. The first thing we noticed in this lab was that when we added an additional lightbulb to our original circuit, the lightbulbs were both dimmer, and the current decreased. For series circuits, the total resistance of the circuit can be found by adding values for all the resistance together. This relationship can be seen as Req (total resistance) = R1+R2... However for circuits in parallel, the relationship between 2 resistance in parallel in relation to the total resistance of the circuit can be shown as 1/Req=1/R1+1/R2.
The next principle we learned to apply to solving circuits were Kirchhoff's Voltage Law and Kirchhoff's Current Law. Kirchhoff's Voltage Law is based on the conservation of energy, where the total amount of energy gained per unit charge (voltage gained) must be equal the amount of energy lost per unit charge (voltage dropped) as both energy and charge are both conserved.
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| As shown by the voltmeter, the voltage drop over each light bulb is 4.50 V which when added together, equals the voltage of the battery (9.00 V). |
I in = I out.Using these concepts we are able to solve both series and parallel circuits. For series circuits, we must first find the total resistance of the circuit, which is a concept we learned through the virtual lab by adding the resistances together. With this, we are able to solve for the total current of the circuit if we already know the voltage the battery produced. Since we know that the current stays constant through a series circuit, we can now solve for each voltage drop over each resistance in the circuit by using the total current, and the resistance to solve for V(V=IR). With our knowledge of Kirchhoff's Voltage Law, once we find each individual voltage drop, we know we have correctly solved the circuit by adding each voltage drop together, which should equal the voltage produced by the battery.
For parallel circuits, we can find the total resistance of the circuit by using 1/Req=1/R1+1/R2... to once again find the total current of the circuit. With the total current we can find the voltage drop using V=IR. Once we have found the total current of the circuit and the voltage drop, we can expand backwards to find how the current splits. Since the voltage across each branch is the same, we can solve for I using the individual resistances and the voltage for each branch.
The next concept we learned about was electrical power. As we learned, when a charges flows through a resistor, it loses energy due to collisions with the atoms in the wire. This energy loss is transformed into heat energy and is related to voltage drop since V=PE/q. Because power is the rate of doing work at which energy is transformed, Joules Law states that P=VI. In addition P=I^2R or P=V^2/R. To further extend this, we can also find electrical energy, since E=P(t) where t is time. Since a joule is a very small unit, we can use the kilo Watt-hour to represent energy. With being able to solve parallel and series circuit, we could also solve combination circuits, which combine principle from being able to solve both types of circuits.
The last section of this unit we learned was terminal voltage. Terminal voltage is the voltage (potential) difference between the terminals of a battery when connected to a circuit. This is because the battery contributes to some resistance to a circuit, also known as internal resistance. Where terminal voltage is the actually voltage that goes through the circuit, electromotive force or EMF is the maximum voltage that the battery can produce. When a cell is specifically being charged by another cell, the current flows backward therefore Vt (terminal voltage) = E (EMF) + IR (internal resistance), however when the cell is supplying current to the circuit, Vt = E - IR.
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| http://tap.iop.org/electricity/emf/121/page_46054.html |
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