In the animation you can see:Current                                                                     The battery or so...
As the monkey does work on the positive charge, he increases the               3. Resistors – objects that are designed to...
the wire gets longer, and the average drift velocity of electrons    decreases. The correct term for this ‘electric slope’...
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Physics ohm’s law

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Physics ohm’s law

  1. 1. In the animation you can see:Current The battery or source is represented by an escalator which raises charges to a higher level of energyCurrent, or electric current, is the rate of flow of electric charge As the charges move the resistor, represented by the paddle wheel,through a medium. This charge is typically carried by moving electrons they do work on the resistor and as a result, they lose theirin a conductor such as a wire. It can also be carried by ions in an energyelectrolyte, or by both ions and electrons in plasma. By the time each charge makes it back to the battery, it has lost allSimple terms: Current is what flows on the wire like water flowing energy given by the batterythrough a hose. As the charges move through the wire, they lose no energyCurrent flows from negative to positive on the surface of a conductor. The potential drop (negative potential difference) across theIt is measured in amperes or amps. resistor is the same as the potential rise (positive potential difference) across the battery. This demonstrates that a charge can only do as much as was done on it by the battery.Circuits The charges are positive so this is a representation of Conventional Video: http://www.youtube.com/watch?v=9iQhL3VTDb8 Current (the apparent flow of positive charges)There are several kinds of circuits; however, we will only discuss the The charges are only flowing in one direction so this would besimple circuit. considered direct currentSimple CircuitA simple circuit is fund everywhere in the world, in homes, offices andother places.The simple circuit requires three things for it to work: Voltage 1. A source of electrical potential difference or voltage Video: http://www.youtube.com/watch?v=Lklai_KXGxg 2. A conductive path 3. An electrical resistor Also called:Despite the materials being simple, it is quite useful and common. They Potential differenceexist in flashlights, ceiling lights, doorbells, and many kitchen Potential dropappliances. Below is an animation of what goes on in a simple circuit Electrical potential differencewhere the electrical energy is shown as gravitational potential energy Electrical potential energy(GPE). It is the difference in electrical potential between two points, or in the difference in electrical potential energy per unit charge between two points.
  2. 2. As the monkey does work on the positive charge, he increases the 3. Resistors – objects that are designed to have a specific resistanceenergy of that charge. The closer he brings it, the more electrical so that they can dissipate electrical energy or modify how apotential it has. When he releases the charge, work gets done on the circuit behavescharge which changes its energy from electrical potential energy to Objects such as wires that are designed to have low resistance so thatkinetic energy. they transfer currents with the least loss of electrical energy are calledEvery time he brings the charge back, he does work on the charge. If he conductors. Objects that are designed to have a specific resistance sobrought the charge closer to the other object, it would have more that they can dissipate electrical energy or otherwise modify how aelectrical potential energy. If he brought 2 or 3 charges instead of one, circuit behaves are called resistors. Conductors are made of highlythen he would have had to do more work so he would have created conductive materials such as metals, in particular copper andmore electrical potential energy. Electrical potential energy could be aluminum. Resistors, on the other hand, are made of a wide variety ofmeasured in joules just like any form of energy. materials depending on factors such as the desired resistance, amountSince the electrical potential energy can change depending on the of energy that it needs to dissipate, precision and cost.amount of charge you are moving, it is helpful to describe the electrical Factors Affecting Resistancepotential energy per unit of charge. This is known as electrical 1. The nature of the material – some materials are better conductorspotential. than others, causing less resistance. The more tightly an atomElectrical potential – at a point within a definite space is equal to the holds on to its outermost electrons the harder it will be to make aelectrical energy (measured in joules) at that location divided by the current flow. The electronic configuration of an atom determinescharge there (measured in coulombs) how willing the atom will be to allow an electron to leave and wander through the lattice. If a shell is almost full, the atom is reluctant to let its electrons wander and the material it is in is inResistance an insulator. If the outermost shell (or sub-shell with transition metals) is less than half full then the atom is willing to let those electrons wander and the material is a conductor 2. The thickness of the conductor/wire – the larger the wire, the lessResistance is how much an object resists the flow of electrons. It is the resistance; the bigger the cross sectional area of the wire theinverse of conductance. It measures how difficult it is for electrons to greater the number of electrons that experience the ‘electricflow through a material. It is measures in ohms. slope’ from the potential difference. As the length of the wireThink of current like water flowing through a hose, if there is nothing does not change each cm still gets the same number of voltsin the hose, then the water will flow freely. However, if there is a across it – the potential gradient does not change and so thesomething blocking the hose such as leaves, small animals, pebbles, etc. average drift velocity of individual electrons does not change.then it will be harder for the water to flow through. Although they do not move any faster there are more of themConductors, Insulators and Resistors moving, so the total charge movement in a given time is greater 1. Conductor – a material which contains movable electrical and current flow increases. This does not give rise to a straight charges. In metallic conductors such as copper and aluminum, line graph as cross sectional area is inversely proportional to the movable charged particles are electrons resistance not directly proportional to it. 2. Insulator – a material that is a poor conductor of electricity. 3. The length of the conductor/wire – the longer the wire, the more - An insulator, such as ceramic or rubber, has high resistance; if you take a wire of different lengths and give each a resistance and poor conductance. A metal has low particular potential difference across its ends. The longer the resistance and high conductance wire, the less volts each cm of it will get. This means that the ‘electric slope’ that makes the electrons move gets less steep as
  3. 3. the wire gets longer, and the average drift velocity of electrons decreases. The correct term for this ‘electric slope’ is the potential gradient. A smaller potential gradient (fewer volts per meter) means current decreases with increased length and resistance increases.4. The temperature – heat affects resistance, the higher the temperature the higher the resistance. When you cool a certain material to a the point where it reaches its critical temperature, its resistance would equal zero. But if you increase its temperature, you’d give more energy to its atoms, this increasing the number of collisions between them resulting in increasing the resistanceOhm’s lawOhm’s Law describes mathematically the relationship between current,voltage (potential difference) and resistance. The more potentialdifference you have, the greater your current is going to be. The moreresistance a circuit has, the lower the current is going to be. The I is the current through the conductor in units of amperes;following equation describes Ohm’s Law. It holds true for any circuit aslong as temperature does not change. V is the potential difference measured across the conductor in units of volts; and R is the resistance of the conductor in units of ohms. The potential difference (voltage) is proportional to the current through it. The current is indirectly proportional to resistance.

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