Series and parallel current circuits
Electric current
An electric current is the movement(flow) of an electrical charge. Current consists of negatively charged particles that are called electrons. In the 19th century scientists knew little about an electric current, and they assumed that electrical current was the flow of positive charges and they compiled many rules and laws about this.
Electric current
In the 19th century scientists knew little about an electrical current, and they assumed that electric current was the flow of positive charges and they compiled many rules and laws about this. Rather than change the rules and laws, they decided according to a convection (an agreement) to view electrical current as the flow of a positive charge from the positive pole to the negative pole of the cell of a battery. A flow of charge in this direction (flow of negative charge) is known as coventional current. An electron current (flow of negative charge) is precisely the opposite and flows from negative to positive. According to conventional current direction as the flow of positive charge from positive to negative.
Measurement of current
Current is measured by means of an instrument that is called an ammeter. The unit in which the magnitude of the current is measured, is called ampere (A). The international symbol for current is I.
1) An ammeter is always connected in series in a circuit
An ammeter is used to measure the current in ampere(A); for that reason the entire current has to flow through the instrument. An ammeter has a low resistance and therefore offers little or no resistance to the flow of current.
2) The polarity must be correct
An ammeter has a black (negative) contact socket and one or more red (positive) contact sockets. Negative (black) to negative pole of the cell or attery. The positive red contact socket to the positive pole of the cell or battery. If connected incorrectly, the ammeter nay be damaged.
Voltage or potential difference
Voltage or potential difference is the difference in electrical potential energy per charge between two different points in an electrical circuit. A simpler explanation is as follows: voltage or potential difference tells us how much electrical potential energy is lost by the charges when they flow through a resistor, or how much they gain when they flow through a cell or battery.
Measurement of voltage or potential difference
Voltage or potential difference is measured by means of an instrument that is called a volt meter. The unit in which th magnitude of voltage or potential difference is measure, is called a volt. (V) Symbol foor voltage or potential difference is V. The entire current does not have to flow through the instrument. The volt meter is therfore not connected like an ammeter in series.
1) A volt meter is always connected to a component in parallel
When a volt meter is connected to a cell or battery in parallel, we say it measure the cell or battery's capacity to deliver current.
2) The polarity must be correct
As in the case of the ammeter, a volt meter also has a black (negative) contact socket and one or more red (positive) contact sockets. The black (negative) contact socket to the negative pole. The red (positive) that leads to the positive pole.
Resistors
A resistor is an electrical component that is specially manufactured and connected in a circuit to offer resistance against the flow of current, and in so doing, to control the current and voltage in the circuit.
Rheostat
A resistor whose resistance can be changed. A rheostat is therefore an adjustale resistance.
Cells connected in series
The total voltage will be the sum of voltages (potential differences) of individual cells. 1,5V + 1,5V + 1,5V + 1,5V=6V Can deliver a stronger current than one single cell.
Cells connected in parallel
The voltage over them will be the same as for only one cell. Over the four cells connected in parallel is 1,5V. Deliver the same current as one cell, but it can maintain the current for a longer period -the current strength is being shared by the four cells, thus cells would last four times longer than when a single cell is used in a circuit.
Series circuits
The current through all the resistors is the same because the readings on A1=A2=A3=A4.
Sum of the volatges V1(battery)= V5 (over all the resistors together)
=V2+V3+V4
The resistor with the highest resistance will have the greatest volt meter reading (voltage), and the resistor with the smallest resistance will have the smallest volt meter reading (voltage). Resistors in series are referred to as voltage distributors (or potential difference distributors). As more resistors are connected in series in the circuit, the total resistace of the circuit increases, while the main current (total current) decreases in the circuit-for the same battery.
Parallel circuits
The current is eing branched and the current divided. The largest part of the divided current flows through the resistor branch with the lowest resistance. The largest part of the divided current flows through the resistor branch with the lowest resistance with the lowest resistance. The main current (total current) through the battery is the same as the sum of the currents through the resistors.
A1(main current)=A2 (main current)
=A3 (branch current) + A4 (branch current)
V2 (over the parellel resistors together)=V3=V4=V1 ( over the battery)
Reference is made to parallel resistors as current distributors. As more resistors are connected in parallel in parallel in the circuit, the total resistance of circuit decreases, while the main circuit (total current) in the circuit increases-for the same battery.
Lighting system in our homes
The lighting in our homes is normally connected in parallel. If one light bulb blows, the rest if the lights will still work, because each one of them is connectedto the main circuit through their own parallel circuit. The electrical power supply to our houses is approximately 220V and 60A. It is a high voltage and a strong current, and can be dangerous if it is not handled correctly. The main current that flows to our home, is distried at the circuit panel in a numberr of parallel circuits. These parallel circuits lead to the stove circuit (for the stove), the heating circuit (for the geyser), the light circuit (for the lights of a home), and the circuit consisting of main circuits (for appliances that work with three point plugs).
Relationship between voltage, current and resistance
Resistors are added to a circuit in order to reduce the magnitude of current that is flowing. The greater the resistance value, the lower the current. The unit of resistance is the ohm. The current that flows through a resistor at a constant temperature, is proportionate to the current through the resistance. This is called Ohm's law and is represented as follows in an equation.
Safety with electricity
The wires and other components in the circuit heat up, which may cause an electric fire. This includes fuses, circuit reakers and earth leakage breakers.
Fuses
A fuse is used to protect a circuit against the heating effect of an electric current. A fuse consists of very thin piece of wire with a low melting point which is connected in series in a circuit so that all the available current may flow through it. The current flows through the wire and when the current becomes too strong, the wire becomes hot and melts. The current stops flowing. A fuse should be replaced when it has melted. Some old houses have fuses for the protection of wiring in house.
Circuit breakers
Circuit breakers are electric switches (electromagnet) that are connected to a room or appliance that automatically switches off the flow of an electric current when a overload or short circuit occurs. If the current becomes too strong, the circuit breakers trip in order to prevent an overload, interrupting the current. Contrary to the situation posed by a fuse, the switch may be switched on again after the problem has been solved.
Earth leakage circuit breakers
The earth leakage circuit breaker is a safety device that is able to switch off the electricity supply to all the circuits in house when a current of 30 mA or more leaks to the ground. It prevents further damage to faulty wiring or appliances and protects people against injuries or death as a result of an electric shock. It limits the amount of current that can move through the human body, and the time that it takes for the charges to move. Electrical current that is not strong enough to cause an ordinary circuit breaker to trip, is strong enough to cause injury to a person, and even fatally shock a person. Amount of current that is drawn through the charged wires in a circuit differs from the quantity that returns through the neutral wire, the breaker immediately cuts the power. This can happen when current from damaged wires or another short circuit, leaks through the body of a person into the ground. The reaction of the earth leakage circuit reakers is normally quick enough to prevent a fatal shock or serious burns- it shuts off all of the current as a safety.
Household wiring
Our houses therefore have to be correctly wired to make it possible for all these appliances to be used. Let us look at the most important components that are found in.
1.The mains-Electricity from the power station is brought to the meter box by means of overhead wiring or underground cables.
2.The meter box-The meter box (electricity meter) is usually outside against the wall of the hous. For houses that use prepaid electricity, the meter box (prepaid electricity meter) is in the house, so that one can see how many units of electricity are still available. Electricity flows through the meter in the meter box to the distribution board in the house.
3.The distribution board-This is found in the house and contains the following components:
-main switch that is used to switch the electricity supply in the house on and off.
-earth leakage circuit breaker(s) that secures all the different circuits in the house.
-circuit breakers that secure all the different circuits in the house.
4.Circuits through which electricity is distributed to different places in the house, and from where different electrical appliances are connected in parallel.