Electrical Resistance
Electrical resistance is a property of an electrical circuit that
opposes the flow of current. Resistance involves collisions of the
current-carrying charged particles with fixed particles that make up
the structure of the conductor. Resistance is often considered as
localized in such devices as lamps, heaters and resistors in which it
predominates, although it is a characteristic of every part of a
circuit, including connecting wires and electric transmission lines.
In circuits where the current (I) and voltage (V) are related by a
simple proportionality constant, as in OHM'S LAW,
V = RI, the proportionality constant R is the resistance of the
circuit. This discovery was made by Georg Simon Ohm (1787-1854), a
German physicist, therefore, Ohm is the common unit of electrical
resistance.
Resistance is the property of an electric circuit or part of a circuit
that transforms electric energy into heat energy. The dissipation of
electric energy in the form of heat, even though small, affects the
amount of electromotive force, or driving voltage, required to produce
a given current through a circuit. The resistance of a circuit
element, expressed in ohms, can be calculated from the following
formula, which gives the power P, in watts, converted into heat by a
resistance of R ohms, when a current of effective value I amperes
flows through the element:
P = RI2 , R = P / I2
The resistance of a wire is directly proportional to its length and
inversely proportional to its cross sectional area, so the longer the
wire, the greater resistance to the flow of charge and as the cross
sectional area of a wire increases the resistance decreases:
R = K / A (K = constant, A = area)
Resistance also depends on the material of the conductor. For example
if you pass electricity through a wire made of a pure metal it will
have less resistance than a wire which is made up out of a metal
alloy. This is because the atoms in a pure metal are all equal in size
I also decided to use a wooden block to keep hold of the wire, because
longer it will take electrons to get to the end of the wire. This is
have to be across the wire and not just anywhere in the circuit so it
V is voltage in volts and I is current in amperes. L:- is the length
50cm for us. The current will be kept on the same level using the same
Factors Affecting the Resistance of a Wire The aim of this experiment is to investigate one factor that affect the resistance of a wire. I will do this by performing an experiment. First I will need to identify the factors that effect resistance. There are a few factors that affect the resistance, it is determined by the properties an object has.
Investigating the Effect the Thickness of a Wire has on Its Resistance. Equipment:.. Nickel Wire cut into 10 pieces of 30cm length (Ruler, Pliers). Two crocodile clips Five Pieces of Wire Power Source Variable Resistor Ammeter Volt Meter Method: The.. =
An Investigation into the Relationship Between the Resistance of a Wire and Its Diameter and Length
Investigating the Factors that Affect the Resistance of a Wire. Aim To study the factors that affect the resistance of a wire. Background Information Current and potential differences measure different things. they are related to each other.
This means that I expect a graph of R versus L to be of the form:
do this I will need to make sure that I am using the milliamp/volt or
Super conductivity is a natural phenomenon in which certain materials such as metals, alloys, and ceramics, can conduct electricity without resistance. These materials are what we call superconductors. In a superconductor, once the flow of electrons begins, it essentially goes on forever, making it an important material to humans. Superconductivity was discovered by a Dutch scientist by the name of Heike Kamerlingh Onnes in 1911. While researching properties of materials at absolute zero, this man found out that certain materials lost its resistance to the flow of electrons. For years to come, his discovery was at the head of theoretical interest. The only problem though, was that people at that time could not even think of a way to produce such a temperature, to allow materials to be superconductors at all times. This all changed in 1986 when Karl Muller and George Bednorz were working at the IBM Research Division in Zurich, Switzerland. They found a material that reached superconductivity at around 35 degrees Kelvin or –238 degrees Celsius. In the next year, a team of Chinese-American physicists declared that they had found a material that reached superconductivity at 92 degrees Kelvin. This was a big improvement. 92 degrees Kelvin is not a very high temperature, in fact, it is the equivalent of –181 degrees Celsius. Locating superconducting material above 77 degree Kelvin is a good thing because it means that the material will be easily produced and used. A theoretical understanding of superconductivity was advanced in 1957 by American physicists John Bardeen, Leon Cooper, and John Schrieffer. Their Theories of Superconductivity became know as the BCS theory (which came from each mans last name) and won them a Nobel prize in 1972. The BCS theory explained superconductivity at temperatures close to absolute zero. However, at higher temperatures and with different superconductor systems, the BCS theory has consequently became insufficient to fully explain electron behavior. The Type 1 category of superconductors is basically made up of pure metals that normally show conductivity at room temperature. They require really cold temperatures to slow down molecular vibrations enough to facilitate unrestrained electron flow in agreement to the BCS theory. BCS theory suggests that electrons team up in cooper pairs in order to help each other overcome molecular obstacles. Type 1 superconductors were discovered first and require the coldest temperatures to become superconductive. They are characterized by a very sharp transition to a superconducting state.
An alloy is a homogenous mixture of a metal with one or more other elements which are usually other metals.
of the atoms, so if there are more or larger atoms then there must be
Numerous factors influence electrical conductivity and resistance, two of them are temperature and length of the wire (these are external factors). Electrical conductivity is defined as the property used to describe how well materials allow electrons to flow, and the degree to which a specific material conducts electricity., Electrical conductivity is calculated as the ratio of the current density in the material to the electric field that causes the flow of current. The SI unit of electrical conductivity is Siemens per meter (S/m). Electrical conductivity is also commonly represented by the Greek letter σ (sigma), but κ (kappa) (especially in electrical engineering) or γ (gamma) are alsowhich are occasionally used. Electrical resistivity quantifies how strongly a specific material opposes the flow of electric current. Electrical resistivity is commonly represented by the Greek letter ρ (rho). The SI unit of electrical resistivity is the ohm⋅metre (Ω⋅m) although other units like ohm⋅centimetre (Ω⋅cm) are also in use.