BBC - GCSE Bitesize: Voltage, current and power
The cost of electricity depends on the power rating of the appliance used, how long it is used for, and the price of a unit of electricity. You can work out power using this equation: What is the power if the voltage is 12V and the current is 5A?. Electronics Tutorial about the Relationship between Voltage Current and Voltage, (V) is the potential energy of an electrical supply stored in the form of an. Basically for all practical purposes the circuit or bulb or any other appliance of resistance of an appliance - which is essential for different power output from different appliances. What is the relationship between power, current and voltage?.
In our battery diagram above, if we remove the bulb and reconnected the wire so the battery was short circuited, the wire and battery would get very hot and the battery would soon be flat because there would be virtually no resistance in the circuit. Without any resistance, a huge electrical current would flow until the battery was empty. Once we add a bulb to the circuit, resistance is created.
There is now a local "blockage" or narrowing of the pipe, per our water pipe analogy where the current experiences some resistance. This greatly reduces the current flowing in the circuit, so the energy in the battery is released more slowly. As the battery forces the current through the bulb, the battery's energy is released in the bulb in the form of light and heat.
In other words, the current carries stored energy from the battery to the bulb, where it is turned into light and heat energy. The image above shows a light bulb as the main cause of electrical resistance. A watt is the base unit of power in electrical systems.
It can also be used in mechanical systems.
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It measures how much energy is released per second in a system. In our battery diagram, the size of both the voltage and the current in the bulb determine how much energy is released.
Basic electrical quantities: current, voltage, power (article) | Khan Academy
In the diagram above, the light bulb would get brighter as the power, measured in watts, increases. We can calculate the power released in the bulb, and of the electrical system as a whole, by multiplying the voltage by the current.
So, to calculate watts, the following formula is used. As mentioned above, when current flows through the resistance of a load, it gets hot. This is sometimes the desired effect, e. However it is an unwanted effect in lamps, because the desired function of the device is to convert electricity to light, and not produce heat as a byproduct.
Excessive current in power cables during an overload can potentially cause a fire if protective devices such as fuses or MCBs Miniature Circuit Breakers aren't included in line with the cable.
So what else happens when current flows through a conductor? One effect is that a magnetic field is produced. This phenomenon is used in a device called a solenoid or electromagnet which is basically like a spool or coil of wire through which a current flows.
Electromagnets are used in the old style, non-electronic, door and phone bells, water inlet valves on washing machines, relays a switch operated by an electromagnetstarter motors on vehicles and in salvage for lifting iron and steel. Current flowing through a conductor also produces an electric field. An extreme example of this is the high intensity field produced under a high voltage power line which is sufficient to illuminate a fluorescent tube held in the hand.
The electric field under a high voltage power line is sufficient to produce an electric discharge in a fluorescent tube. As you've discovered, if resistance is increased in a circuit, current decreases. If you just break the conductor in a circuit and create an air gap, the magnitude of the resistance for all practical purposes is infinite because air is a good insulator and no current will flow. Two contacts, usually made of brass in a domestic switch, are pressed together when the switch is on and closed.
When the switch is turned off, the contacts rapidly separate and interrupt current. Imagine two electrodes or points in a circuit separated by an air gap e. If voltage is high enough, the air between the two points becomes so stressed by the electric field that it becomes ionized, i. These electrons are then able to traverse the gap, attracted by the positive electrode and in doing so, collide with other gas molecules and release more electrons.
Voltage, current and power
Eventually an avalanche of electrons occurs all of this happening in a split second and the result is called a spark or spark discharge A spark produces a flash of visible light, heat, UV radiation and sound and it's temperature can be about deg C, hotter than the surface of the sun.
The voltage required to produce a spark is about volts per mm between rounded electrodes in air.
Sparks can be small, e. An example of a large spark is lightning. When clouds get charged up, voltage becomes so high that a spark jumps from cloud to cloud or cloud to ground. The sound we call thunder is caused by the explosive heating and expansion of air by the electrical discharge.
Sparks occur in an air gap when voltage exceeds the breakdown voltage of the gap. When two electrodes are separated, current tends to continue to flow and heating of the metal electrodes causes material to vaporise and also ionise the air.
This results is a continuous spark discharge called an arc which is similar to a spark. If the electrodes are separated sufficiently, the arc won't be sustained and will stop abruptly. Arc welding makes use of an arc between two electrodes to melt metal. Switches must also be designed so that their contacts separate sufficiently apart and quickly enough so that arcs are rapidly quenched and reduce damage to the contacts.
electrical resistance - Power in Series Combination Of Appliances - Physics Stack Exchange
In substations, large air gaps or oil filled circuit breakers are necessary to quench the high current arcs which occur when high voltage is switched. A voltage regulator is an electronic device used to keep the voltage output of a power supply at a constant level, independent of current drawn by a load. In general, these devices are implemented as single ICs in a variety of package formats, or as separate modules consisting of several discrete components or integrated circuits.Question EE-03 - Power ratings of Home Appliances in Hindi.
A regulator that reduces voltage is called a buck regulator and one that increases voltage is called a boost regulator. The output of an unregulated voltage supply will drop as current increases. This is because of internal resistance which causes a potential drop as current flows. This drop subtracts from the idealized internal voltage source and causes the output of a source to be lower than the open circuit voltage without a load.
What are Voltage Regulators Used For? To stabilize the voltage powering electronic circuitry so that it behaves consistently Vehicle alternators incorporate voltage regulators e. There are two types of regulator, the linear regulator and switching regulator. A linear regulator is a semiconductor device, but effectively works as a controlled dropper resistor in series between the input supply and the regulator output.
So it drops voltage from eg 12 volts to 5 volts. The regulator monitors its output voltage and if the load tries to take more current and op voltage tries to fall, the resistance of a pass transistor is reduced so that it drops less voltage in order to maintain the output at a constant 5 volts.
Similarly if the load takes less current, the resistance increases. Disadvantages of Linear Regulators Since the regulator is in series with the load, the current supply from the source is the same as that supplied to the load.
However since voltage is dropped by the regulator, power is wasted as heat in the device.
The lower the input voltage the better, and a small or large heat sink may be needed, depending on the ambient temperature and voltage drop. Basic regulators need about a 2 volt difference between input and output voltages to work, but low dropout regulators are available which can work with a smaller difference between IP and OP.
Switching Regulators A switching regulator on the other hand works differently. The duty cycle how long the pulse is on of the switching waveform is varied depending on the demand of the load in order to keep the op voltage constant. Two wires are needed because electricity flows in a loop.