CURRENT ELECTRICITY
The study of sustained movement of electric charge is called electric current. To maintain the flow of electric charge two things are required, first there must be sources of electric charge capable of moving and a way of causing them to move. The second there must a closed path around which the charges move ultimately returning to the source. This closed path is called an electric circuit. The copper wires are normally used as pathways of the electric current to flow.
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.
The size of the electric current in a material depends on the number of charge carrier taking part and the speed at which they are moving. In a simple electric circuit the charge carriers are the electrons.
Electric current is a fundamental quantity and is the amount of charge passing a given point in a circuit divided by the time required for the passage of the charge.
An electric current is a flow of electric charge. In electric circuits this charge is often carried by moving electrons in a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons.
The SI unit for measuring an electric current is the ampere, which is the flow of electric charge across a surface at the rate of one coulomb per second. Electric current is measured using a device called an ammeter. Electric currents cause Joule heating, which creates light in incandescent light bulbs. They also create magnetic fields, which are used in motors, inductors and generators.
The particles that carry the charge in an electric current are called charge carriers. In metals, one or more electrons from each atom are loosely bound to the atom, and can move freely about within the metal. These conduction electrons are the charge carriers in metal conductors.
So
The SI unit of electric circuit is ampere (A) other units are milliampere (mA), kiloampere (kA) and microampere.
An ammeter is used to measure electric current
A coulomb is the quantity of electricity which passes a given point in a circuit in 1 second when a steady current of 1 ampere is flowing.
Uses of current electricity
Current electricity is mainly used for:
Cooking
Lighting
Communication; and
Heating
Sources of Current Electricity in Everyday Life
All sources of electric currents work by converting some kind of energy into electrical energy. The two basic sources are:
Batteries e.g. Mobile phone battery, car dry cell batteries and also car alternator.
Generator
All sources of electric current work by converting some kind of energy into electrical energy. The two basic sources are batteries and generator. Batteries convert chemical energy into electrical energy while generators convert mechanical energy into electrical energy.
Other sources of electric energy include water (hydroelectric power), water current i.e ocean waves, solar energy and wind energy. Hydroelectric power is very reliable except times of severe drought. This is because electricity is generated from water in dams and waterfalls which depend on rainwater.
Solar cells trap and convert radiant energy into electric energy. Spaceships and satellites use solar cells to convert sunlight into electricity.
Simple electric circuit
An electric circuit contains a source of moving charge (battery or generator), connecting wires made up of conducting material (usually copper metal) and various electrical devices such as bulbs, switches, resistors, ammeters and voltmeters.
Voltmeter is used to measure potential difference in volts while resistors oppose the flow of the current. The circuit may also contain devices for controlling the amount of current. These include rheostat, fuses and circuit-breaker as well as devices for measuring current such as ammeter and galvanometer.
Note: Potential difference or voltage is a measure of electrical energy.
Potential difference between the positive and negative terminals of a battery causes a current to flow along any conducting path that links them.
Qn. List five circuit components and state their functions.
The concept of current, voltage and resistance
An electric current in a material is the passage of charge through the material. In metals, the charge is carried by free electrons. In solutions, such as sodium chloride, it is carried by charged particles known as ions. In insulators like plastic and wood do not contain charge carriers at all as every electron is firmly fixed onto their atoms. The electrons are not free to move. The rate of flow of the electrons in a material is called electric current.
A current of 1A is equivalent to a flow of 6.25 x 1018 electrons per second, and 1 electron has a charge of 1.6 x 10-19 C.
Example
An electric current of 0.12A passes a point B along a conducting wire. How much electric charge is flowing past this point in a minute?
Solution
Charge = current x time
Q = 0.12A x 60s
The amount of charge flowing past this point in a minute is 7.2C
Voltage
When several cells have been joined together, they form a battery. Every cell has a voltage, commonly referred to as potential difference across its terminals. Voltage is measured using voltmeter and its SI unit is volt (V). Always the voltmeter is connected across the appliance.
Resistance
As current flows through the circuit, it encounters some opposing force. This force determines the amount of current flowing in an electric device. Therefore, flowing current depends on the voltage (pd) across the device and the nature of the device. The property of conductors that oppose the flow of electric charges depends on the relationship between current and voltage across their ends as discovered by George Ohm.
Hence,
R is the constant of proportionality. This constant is called resistance and the above relationship is known as Ohm’s law.
Therefore a resistance of 1 ohm is obtained when a p.d of 1 V causes a current of 1A to flow in a circuit.
Resistance is measured in ohms (). Other units are kilohms () = , megaohm () = , milliohms (() = and microhms () = .
A resistor is a device specially designed to offer resistance to the flow of an electric current. Resistors include rheostat (variable resistor) and fixed resistors.
Materials that allow current to pass through them directly proportional to the p.d across them, at a steady temperature are said to obey ohm’s law. These materials are referred to as Ohmic conductor.
Ohm’s law states that “at constant temperature and other physical factors, a current passing through a wire (conductor) is proportional to the potential difference across its ends”.
Therefore from ohms law
Factors affect resistance of a conductor;
Length of a conductor
Temperature
Type of material
Cross-sectional area
Length of a conductor: The longer the wire, the higher the resistance. Therefore the length of a conductor is proportional to the resistance of a wire.
Temperature: the higher the temperature of the wire the higher the resistance of the conductor, and vice versa. The resistance of most metal conductor increases with the increase in temperature.
Type of material: The conducting ability of the material has to be considered. A nichrome wire has more resistance than a copper wire of the same dimension.
Cross-sectional area: A thin wire has more resistance than a thick conductor. With all other factors being equal, a long wire has more resistance than a short wire and a thin wire has more resistance than a thick one.
Examples
A battery of 5 V has a resistance wire of 20 connected across it. Calculate the current in the circuit.
An ohmic conductor has a voltage drop of 9 V measure across it. The current flowing in the conductor is 3 mA. What is its resistance?
Note: for a single loop or simple circuit;
Current is the same at all points around the circuit.
The sum of the potential differences around a conducting path from one battery terminal to the other terminal within the circuit is the same as the p.d across the battery.
Example:
Calculate the readings of the voltmeter P and the ammeter Q in the circuit below.
Combination of resistors:
There are two main methods of connecting circuit components, in series and parallel.
Series combination
In series arrangement the resistor are connected end to end.
In simple circuit
V = V1 + V2 or V – (V1 + V2) = 0
This means that the sum of the potential difference across the resistors is the same as pd across the battery.
The current is the same at all points round the circuit.
From ohms’ law the total resistance
But the current flowing through the resistors is the same;
Therefore the total resistance for resistor in series is equal to the sum of individual resistance.
Parallel combination
Resistors are connected across two common points in a parallel arrangement.
The potential difference is from a single source and so is the same for all the branches; however the current is different in each branch.
From ohms’ law
From
Therefore;
then,
Examples:
Three resistors 2, 4 and 7 are connected in series to a 3 V battery. What is the current in the circuit?
Find the equivalent resistor for a three resistors 50, 44 and 67 when they connected in;
Series (ii) parallel
What would be the effect on the resistance of a conductor if;
Its length is increased?
Its temperature is increased?
Its cross-sectional is reduced?
The study of sustained movement of electric charge is called electric current. To maintain the flow of electric charge two things are required, first there must be sources of electric charge capable of moving and a way of causing them to move. The second there must a closed path around which the charges move ultimately returning to the source. This closed path is called an electric circuit. The copper wires are normally used as pathways of the electric current to flow.
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.
The size of the electric current in a material depends on the number of charge carrier taking part and the speed at which they are moving. In a simple electric circuit the charge carriers are the electrons.
Electric current is a fundamental quantity and is the amount of charge passing a given point in a circuit divided by the time required for the passage of the charge.
An electric current is a flow of electric charge. In electric circuits this charge is often carried by moving electrons in a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons.
The SI unit for measuring an electric current is the ampere, which is the flow of electric charge across a surface at the rate of one coulomb per second. Electric current is measured using a device called an ammeter. Electric currents cause Joule heating, which creates light in incandescent light bulbs. They also create magnetic fields, which are used in motors, inductors and generators.
The particles that carry the charge in an electric current are called charge carriers. In metals, one or more electrons from each atom are loosely bound to the atom, and can move freely about within the metal. These conduction electrons are the charge carriers in metal conductors.
So
The SI unit of electric circuit is ampere (A) other units are milliampere (mA), kiloampere (kA) and microampere.
An ammeter is used to measure electric current
A coulomb is the quantity of electricity which passes a given point in a circuit in 1 second when a steady current of 1 ampere is flowing.
Uses of current electricity
Current electricity is mainly used for:
Cooking
Lighting
Communication; and
Heating
Sources of Current Electricity in Everyday Life
All sources of electric currents work by converting some kind of energy into electrical energy. The two basic sources are:
Batteries e.g. Mobile phone battery, car dry cell batteries and also car alternator.
Generator
All sources of electric current work by converting some kind of energy into electrical energy. The two basic sources are batteries and generator. Batteries convert chemical energy into electrical energy while generators convert mechanical energy into electrical energy.
Other sources of electric energy include water (hydroelectric power), water current i.e ocean waves, solar energy and wind energy. Hydroelectric power is very reliable except times of severe drought. This is because electricity is generated from water in dams and waterfalls which depend on rainwater.
Solar cells trap and convert radiant energy into electric energy. Spaceships and satellites use solar cells to convert sunlight into electricity.
Simple electric circuit
An electric circuit contains a source of moving charge (battery or generator), connecting wires made up of conducting material (usually copper metal) and various electrical devices such as bulbs, switches, resistors, ammeters and voltmeters.
Voltmeter is used to measure potential difference in volts while resistors oppose the flow of the current. The circuit may also contain devices for controlling the amount of current. These include rheostat, fuses and circuit-breaker as well as devices for measuring current such as ammeter and galvanometer.
Note: Potential difference or voltage is a measure of electrical energy.
Potential difference between the positive and negative terminals of a battery causes a current to flow along any conducting path that links them.
Qn. List five circuit components and state their functions.
The concept of current, voltage and resistance
An electric current in a material is the passage of charge through the material. In metals, the charge is carried by free electrons. In solutions, such as sodium chloride, it is carried by charged particles known as ions. In insulators like plastic and wood do not contain charge carriers at all as every electron is firmly fixed onto their atoms. The electrons are not free to move. The rate of flow of the electrons in a material is called electric current.
A current of 1A is equivalent to a flow of 6.25 x 1018 electrons per second, and 1 electron has a charge of 1.6 x 10-19 C.
Example
An electric current of 0.12A passes a point B along a conducting wire. How much electric charge is flowing past this point in a minute?
Solution
Charge = current x time
Q = 0.12A x 60s
The amount of charge flowing past this point in a minute is 7.2C
Voltage
When several cells have been joined together, they form a battery. Every cell has a voltage, commonly referred to as potential difference across its terminals. Voltage is measured using voltmeter and its SI unit is volt (V). Always the voltmeter is connected across the appliance.
Resistance
As current flows through the circuit, it encounters some opposing force. This force determines the amount of current flowing in an electric device. Therefore, flowing current depends on the voltage (pd) across the device and the nature of the device. The property of conductors that oppose the flow of electric charges depends on the relationship between current and voltage across their ends as discovered by George Ohm.
Hence,
R is the constant of proportionality. This constant is called resistance and the above relationship is known as Ohm’s law.
Therefore a resistance of 1 ohm is obtained when a p.d of 1 V causes a current of 1A to flow in a circuit.
Resistance is measured in ohms (). Other units are kilohms () = , megaohm () = , milliohms (() = and microhms () = .
A resistor is a device specially designed to offer resistance to the flow of an electric current. Resistors include rheostat (variable resistor) and fixed resistors.
Materials that allow current to pass through them directly proportional to the p.d across them, at a steady temperature are said to obey ohm’s law. These materials are referred to as Ohmic conductor.
Ohm’s law states that “at constant temperature and other physical factors, a current passing through a wire (conductor) is proportional to the potential difference across its ends”.
Therefore from ohms law
Factors affect resistance of a conductor;
Length of a conductor
Temperature
Type of material
Cross-sectional area
Length of a conductor: The longer the wire, the higher the resistance. Therefore the length of a conductor is proportional to the resistance of a wire.
Temperature: the higher the temperature of the wire the higher the resistance of the conductor, and vice versa. The resistance of most metal conductor increases with the increase in temperature.
Type of material: The conducting ability of the material has to be considered. A nichrome wire has more resistance than a copper wire of the same dimension.
Cross-sectional area: A thin wire has more resistance than a thick conductor. With all other factors being equal, a long wire has more resistance than a short wire and a thin wire has more resistance than a thick one.
Examples
A battery of 5 V has a resistance wire of 20 connected across it. Calculate the current in the circuit.
An ohmic conductor has a voltage drop of 9 V measure across it. The current flowing in the conductor is 3 mA. What is its resistance?
Note: for a single loop or simple circuit;
Current is the same at all points around the circuit.
The sum of the potential differences around a conducting path from one battery terminal to the other terminal within the circuit is the same as the p.d across the battery.
Example:
Calculate the readings of the voltmeter P and the ammeter Q in the circuit below.
Combination of resistors:
There are two main methods of connecting circuit components, in series and parallel.
Series combination
In series arrangement the resistor are connected end to end.
In simple circuit
V = V1 + V2 or V – (V1 + V2) = 0
This means that the sum of the potential difference across the resistors is the same as pd across the battery.
The current is the same at all points round the circuit.
From ohms’ law the total resistance
But the current flowing through the resistors is the same;
Therefore the total resistance for resistor in series is equal to the sum of individual resistance.
Parallel combination
Resistors are connected across two common points in a parallel arrangement.
The potential difference is from a single source and so is the same for all the branches; however the current is different in each branch.
From ohms’ law
From
Therefore;
then,
Examples:
Three resistors 2, 4 and 7 are connected in series to a 3 V battery. What is the current in the circuit?
Find the equivalent resistor for a three resistors 50, 44 and 67 when they connected in;
Series (ii) parallel
What would be the effect on the resistance of a conductor if;
Its length is increased?
Its temperature is increased?
Its cross-sectional is reduced?
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