BBC Bitesize - GCSE Combined Science - Electric circuits - Edexcel - Revision 2
Hi In static electricity/ capacitor the voltage (potential) is proportional to the charge. Q = C*V In current electricity, rate of flow of charge, which is. How electrical charge relates to voltage, current, and resistance. a quick way to reference the relationship between voltage, current, resistance, and power. electrical circuits, charge, current, power and resistance with GCSE Bitesize a source of potential difference (voltage) there will be a current flowing around.
So, when we discuss about these values, the behavior of electrons in a closed loop circuit allows charge to move from one place to another.
He described a unit of resistance which is defined by voltage and current. The difference between voltage and current and resistance is discussed below. In this equation, voltage is equal to the current and that is multiplied by resistance.
Basic Circuit Diagram of V, I and R In the above circuit, when the voltage and resistance values are given, then we can calculate the amount of current. The differences between V, I and R are discussed below. The voltage is defined as, it is the potential difference in charge between the two points on a circuit, it is also called electromotive force.
One point has more charge than another. The unit volt is termed after invented by Italian physicist Alessandro Volta. The term volt is represented by the letter V in schematics. The measuring instrument of voltage is the voltmeter.
Voltage is the source and the current is its result, it can occur without current. The voltage gets distributed over different electronic components which are connected in series in the circuit, and in parallel circuit voltage is same across all components which are connected in parallel. The current is defined as it is the rate of flow of electric charge in a circuit. The measuring instrument of the current is an ammeter.
A plasma can be formed by high temperatureor by application of a high electric or alternating magnetic field as noted above. Due to their lower mass, the electrons in a plasma accelerate more quickly in response to an electric field than the heavier positive ions, and hence carry the bulk of the current. However, metal electrode surfaces can cause a region of the vacuum to become conductive by injecting free electrons or ions through either field electron emission or thermionic emission.
Thermionic emission occurs when the thermal energy exceeds the metal's work functionwhile field electron emission occurs when the electric field at the surface of the metal is high enough to cause tunnelingwhich results in the ejection of free electrons from the metal into the vacuum.
Externally heated electrodes are often used to generate an electron cloud as in the filament or indirectly heated cathode of vacuum tubes. Cold electrodes can also spontaneously produce electron clouds via thermionic emission when small incandescent regions called cathode spots or anode spots are formed.
These are incandescent regions of the electrode surface that are created by a localized high current. These regions may be initiated by field electron emissionbut are then sustained by localized thermionic emission once a vacuum arc forms.
These small electron-emitting regions can form quite rapidly, even explosively, on a metal surface subjected to a high electrical field.
Vacuum tubes and sprytrons are some of the electronic switching and amplifying devices based on vacuum conductivity. Superconductivity Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in certain materials when cooled below a characteristic critical temperature. Like ferromagnetism and atomic spectral linessuperconductivity is a quantum mechanical phenomenon.
It is characterized by the Meissner effectthe complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state.
The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of perfect conductivity in classical physics. Semiconductor In a semiconductor it is sometimes useful to think of the current as due to the flow of positive " holes " the mobile positive charge carriers that are places where the semiconductor crystal is missing a valence electron. A battery can be considered fully charged when: The current has dropped below 4 A see note below ; and: The voltage Vi as measured with the indicator has risen above So then the point at which the battery is fully charged, will determined by the criterium that the current should drop below 4 A.
Still voltage Vi must be checked to make sure that the current has dropped to less than 4 A because the battery is charged, since there could be other reasons why the current is so low: The charger runs short of water so its power output is just enough for a few amperes charging current. The nozzle is partially blocked, with the same effect on the power output. There is something wrong with the field current, maybe too many or too few lamps are switched on, the connections are poor or the brushes are wet.
The current indicator is wrong and underestimates the actual current. The most likely cause for this is corrosion of the surfaces in the indicator switch operate the switch a few times to see if it goes back to a normal value.
In this case, the voltage measurement part probably still functions. So to prevent that batteries that are not yet charged, are disconnected because the current is below 4 A for one of those reasons, also voltage Vi should be checked. The graph of fig.
Relationship and Difference Between Voltage, Current and Resistance
For smaller batteries, the state of charge lines would end up closer towards the Y-axis and such batteries might not be fully charged when the current has decreased to 4 A.
Therefor small car batteries can be considered charged when the current has dropped to 2 to 3 A instead of 4 A. So for those batteries, point C should lie at a current of 2 to 3 A. For small batteries, the other points on the charging characteristic remain virtually the same. Still the choice of having point C at a charging current of 4 A seems wise considering: At a higher temperature, a battery accepts charging current more easily, so when reaching point C, it will be charged a bit more than fig.
Suppose the operator will check the battery only once every hour. This means that on average, batteries will be disconnected half an hour after they have passed point C and then they will be charged considerably more see next paragraph. So point C is the minimum at which a battery can be considered charged enough.
On average, batteries will be charged quite a bit more because the operator will only check once in a while. Allowing batteries to be disconnected a bit early means that total charging time see next paragraph will be shorter, which is important because: It means more convenience for users. They can bring their battery late and still have it recharged the same day.
It also means that the charger can serve more users without having to charge during the night. Allowing that batteries are disconnected a bit early reduces the risc that they will be seriously overcharged, which would damage them just like undercharging does.
It is important that operators have a simple and clear criterium for when a battery is charged well enough and point C provides this. Another way of analysing the charging process is by of looking how charging current, battery voltage and some other variables vary over time. This comes down to calculating how much time it takes to go from one state of charge line to the next. As long as the current is constant at After passing point B, the current is no longer constant so that for each traject between two state of charge lines, a mean current must be calculated.
For this, the current at the beginning and at the end of the traject has been read from fig. The results of this calculation are presented in fig. In this figure, also the voltage Vi at the indicator is printed because this is the voltage that is measured on the switchboard.
After 3 hours and 50 minutes, the charging process passes point B and the voltage regulator starts reducing the field current. After 5 hours and 30 minutes, the charging process passes point C and the battery can be considered just charged.
Relationship and Difference Between Voltage, Current and Resistance
After 7 hours, the charging process reaches point D and the battery is charged completely. Charging any further means overcharging and will only damage the battery. The charging process as a function of time. Things will be quite different in case: Batteries have a lower capacity. Then going from one state of charge line to the next higher one will take shorter so total charging time will be less. Also the state of charge lines in the graph of fig. Worn-out batteries will react more or less like batteries with a lower capacity.
Battery temperature is high. If the temperature is higher, batteries can absorb the same charging current at a lower battery voltage, so all state of charge lines move downwards. Unfortunately no graphs like fig.