Resistance Investigation
Knowledge
My prediction is correct because the more thick and shorter a wire is, the lower the resistance, this allows more current to flow but in a thin and longer wire, the resistance is too high, so heat is given off and the current is reduced. The more resistance there is in a circuit, the lower the current.
Electricity from an atom
Electricity comes from an atom. In an atom there are two types of electric charge. Electrons have a negative charge. Protons have a positive charge. When you switch on a light, the electricity flowing through the wires is actually a flow of electrons. A flow of electrons is called a current. The atoms in a metal are packed closely together. Electrons often change places between atoms in a metal. Energy such a battery can push electrons along. They are pushed from a negative charge and are attracted towards a positive.
Conductors
Metals such as coppers are used to conduct the flow of electricity. There are known as conductors and are covered with plastic insulation to make wires. A conductor is any substance or material that allows electric current to push through. Many good conductors are also good conductors of heat. Silver, copper and gold are good conductors of electricity, but copper is by far the cheapest metal of the three. Copper wires are therefore used a great deal to conduct the flow of electricity.
Resistance and resistors
Bulbs do not conduct as well as connecting wire. Scientists say that they have more resistance to electricity. Energy has to be spent in overcoming this resistance. The bulb gives off this energy as heat and light. The more resistance there is in a circuit, the lower the current. Some metals have less resistance than others. I n circuits, the connecting wires are usually made of copper because it has a low resistance.
Resistors are specially designed to provide resistance. They are used in electronic circuits so that the right amount of current is fed to different parts to make them work properly. Below, a variable resistor is being used to control the brightness of a bulb. The variable resistor contains a long coil of thin nichrome wire.
Sliding the control to the right puts more resistance into the circuit, so the bulb gets dimmer.
Heat from resistance
Whenever current flows through a resistance, heat is given off. This idea is used in the filament of a light bulb. It is also used in the heating elements in appliances such as kettles, irons and toasters. The elements normally contain lengths of nichrome wire.
Insulators
Insulators are materials, which do not let electrons flow through. Their electrons are held tightly to atoms, and are not free to move. Examples of insulators are plastics, ...
This is a preview of the whole essay
Sliding the control to the right puts more resistance into the circuit, so the bulb gets dimmer.
Heat from resistance
Whenever current flows through a resistance, heat is given off. This idea is used in the filament of a light bulb. It is also used in the heating elements in appliances such as kettles, irons and toasters. The elements normally contain lengths of nichrome wire.
Insulators
Insulators are materials, which do not let electrons flow through. Their electrons are held tightly to atoms, and are not free to move. Examples of insulators are plastics, glass and rubber.
Electricity
Electric current is the rate of charge flow past a given point in an electric circuit, measured in coulombs/second, which is named amperes. In most DC electric circuits, it can be assumed that the resistance to current flow is a constant so that the current in the circuit is related to voltage and. resistance by Ohm's law
Current flows in an electric circuit in accordance with several definite laws.
Ohm's Law
For many conductors of electricity, the electric current, which will flow through them, is directly proportional to the voltage applied to them. When a microscopic view of Ohm's law is taken, it is found to depend upon the fact that the drift velocity of charges through the material is proportional to the electric field in the conductor. The ratio of voltage to current is called the resistance, and if the ratio is constant over a wide range of voltages, the material is said to be an "ohmic" material. If the material can be characterised by such a resistance, then the current can be predicted from the relationship:
Voltage Law
The voltage changes around any closed loop must sum to zero. No matter what path you take through an electric circuit, if you return to your starting point you must measure the same voltage, constraining the net change around the loop to be zero. Since voltage is electric potential energy per unit charge, the voltage law can be seen to be a consequence of conservation of energy.
The voltage law has great practical utility in the analysis of electric circuits. It is used in conjunction with the current law in many circuit analysis tasks
The electrical resistance of a material is defined as the ratio of the voltage applied to the electric current, which flows through it:
If the resistance is constant over a considerable range of voltage, then Ohm's law, I = V/R, can be used to predict the behaviour of the material. Although the definition above involves DC current and voltage, the same definition holds for the AC application of resistors.
Whether or not a material obeys Ohm's law, its resistance can be described in terms of its bulk resistivity. The resistivity, and thus the resistance, is temperature dependent. Over sizeable ranges of temperature, this temperature dependence can be predicted from a temperature coefficient of resistance
Resistivity and Conductivity
The electrical resistance of a wire would be expected to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made. Experimentally, the dependence upon these properties is a straightforward one for a wide range of conditions, and the resistance of a wire can be expressed as
The factor in the resistance, which takes into account the nature of the material, is the resistivity. Although it is temperature dependent, it can be used at a given temperature to calculate the resistance of a wire of given geometry.
The inverse of resistivity is called conductivity. There are contexts where the use of conductivity is more convenient.
Resistors
Resistors are specially designed to provide resistance. They are used in electronic circuits so that the right amount of current is fed to different parts to make them work properly. Whenever current flows through resistance, heat is given off. This idea is used in the filament of a light bulb.
Moving Coil Meters
The design of a voltmeter, ammeter or ohmmeter begins with a current-sensitive element. Though most modern meters have solid state digital readouts, the physics is more readily demonstrated with a moving coil current detector called a galvanometer. Since the modifications of the current sensor are compact, it is practical to have all three functions in a single instrument with multiple ranges of sensitivity. Schematically, a single range "multimeter" might be designed as illustrated.
Voltmeter
A voltmeter measures the change in voltage between two points in an electric circuit and therefore must be connected in parallel with the portion of the circuit on which the measurement is made. By contrast, an ammeter must be connected in series. In analogy with a water circuit, a voltmeter is like a meter designed to measure pressure difference. It is necessary for the voltmeter to have a very high resistance so that it does not have an appreciable affect on the current or voltage associated with the measured circuit. Modern solid-state meters have digital readouts, but the principles of operation can be better appreciated by examining the older moving coil meters based on galvanometer sensors.
Ammeter
An ammeter is an instrument for measuring the electric current in amperes in a branch of an electric circuit. It must be placed in series with the measured branch, and must have very low resistance to avoid significant alteration of the current it is to measure. By contrast, a voltmeter must be connected in parallel. The analogy with an in-line flowmeter in a water circuit can help visualise why an ammeter must have a low resistance, and why connecting an ammeter in parallel can damage the meter. Modern solid-state meters have digital readouts, but the principles of operation can be better appreciated by examining the older moving coil meters based on galvanometer sensors.
Ohmmeter
The standard way to measure resistance in ohms is to supply a constant voltage to the resistance and measure the current through it. That current is of course inversely proportional to the resistance according to Ohm's law, so that you have a non-linear scale. The current registered by the current sensing element is proportional to 1/R, so that a large current implies a small resistance. Modern solid-state meters have digital readouts, but the principles of operation can be better appreciated by examining the older moving coil meters based on galvanometer sensors.
Voltmeter/Ammeter Measurements
The value of electrical resistance associated with a circuit element or appliance can be determined by measuring the voltage across it and the current through it and then dividing the measured voltage by the current. This method works even for non-ohmic resistances where the resistance might depend upon the current.
Batteries
A battery makes electrons move by conducting material between its terminals.
Batteries use a chemical reaction to do work on charge and produce a voltage between their output terminals. Such voltages have historically been referred to as emf (electromotive force).
Resistance in parallel Circuits
Total resistance gets less when components are in parallel. When components are in parallel there are two (or more) routes for the electric current. This makes it easy for more current to flow out of the battery.
4. Components that do not obey Ohm's Law
Some devices work in slightly different ways.
a) Thermistor
Thermistors have a lower resistance at higher temperatures.
They let more current flow through them at higher temperatures
b) LDR Light Dependent Resistor
Light dependent resistors have lower resistance when there is more light.
c) Diode
A diode lets the current flow one way only, in the direction of the arrow. This means that it has a low resistance when the current is flowing in the direction of he arrow, but a very high resistance when the current tries to flow the other way.