Electricity is a fundamental and versatile form of energy that is essential in our modern world. It is a phenomenon resulting from the movement of electric charges, primarily electrons, through conductive materials like wires and circuits. Electricity plays a crucial role in various aspects of our lives, from powering our homes and electronic devices to driving industrial processes and transportation systems.
Electric charges are fundamental properties of subatomic particles, such as electrons and protons, that play a central role in the behaviour of matter and the interactions between objects.
Types of Charges: Electric charges come in two fundamental types:
Charge Conservation: According to the law of conservation of charge, the total electric charge in a closed system remains constant. This means that charges cannot be created or destroyed; they can only be transferred between objects.
Charge Transfer: Objects can acquire electric charges through various processes, such as:
Opposite Charges Attract, Like Charges Repel: One of the fundamental principles of electric charges is that opposite charges attract each other, while like charges repel each other.
For example:
SI Unit: The standard unit of electric charge is the coulomb (C). One coulomb is defined as the charge that passes through a conductor when a current of one ampere (1 A) flows for one second (1 s).
Quantisation of Electric Charge: The principle of quantisation of electric charge states that the total charge acquired by a body is always a whole-number multiple of the magnitude of the charge on a single electron. Mathematically, this principle can be expressed as:
q = n x e
Where:
q represents the total electric charge acquired by a body.
n is an integer that represents the number of elementary charges (electrons or protons) gained or lost.
e is the charge of a single electron, approximately equal to 1.6 × 10^{−19}
This principle reflects the fundamental nature of electric charge, indicating that charge comes in discrete units or quanta, and it cannot exist as a fraction of the charge of an electron.
Electric potential represents the electric energy associated with a point in an electric field.
When a small positive test charge is placed in the electric field generated by another charge, it experiences a force due to the electric field. To move this test charge against the force of repulsion (or attraction, depending on the charges involved), work must be done on the charge.
The electric potential at a specific point in an electric field is defined as the amount of work done in moving a unit positive charge from infinity (where there is no influence from the field) to that point.
Unit: The unit of electric potential is the volt (V). Specifically, 1 volt at a point signifies that 1 joule of work is done to transport 1 unit of positive charge (1 coulomb) from an infinite distance to that point.
Potential difference, often referred to as "voltage," is a crucial concept in electricity that describes the difference in electric potential between two points in an electric circuit.
Key Points about Potential Differences:
The potential difference between two points in an electric circuit is defined as the amount of work (in joules) needed to move one unit charge (usually one coulomb) from one point to the other.
Electric current is the flow of electric charges, specifically electrons, within a conductor. It occurs when there is a potential difference (voltage) between two points in a circuit, causing electrons to move from a region of higher potential (voltage) to one of lower potential. The flow of charges constitutes an electric current.
An electric circuit is a complete conducting path that allows electrons to move, creating an electric current.
In electric circuits, symbols are used to represent various electrical components to simplify the process of drawing circuit diagrams. These symbols are known as electrical or circuit symbols. Here are some common electrical symbols and their meanings:
These symbols are essential for drawing circuit diagrams accurately.
Ohm's Law is a fundamental principle in physics that describes the relationship between current (I), potential difference or voltage (V), and resistance (R) in an electrical circuit. It states that, at a constant temperature, the current flowing through a conductor is directly proportional to the potential difference across its ends. This can be mathematically expressed as:
Here, R represents the resistance of the conductor in ohms (Ω), and it is a constant that depends on the nature, length, area of cross-section, and temperature of the conductor.
V represents the potential difference (voltage) across the conductor's ends in volts (V).
I represent the electric current flowing through the conductor in amperes (A).
Key Points to Understand About Ohm's Law:
Substances are categorised into three groups based on their electrical resistance: good conductors, resistors, and insulators.
Factors Affecting Resistance of a Conductor:
The resistance of a conductor is a property that opposes the flow of electric current through it. It depends on several factors:
Resistivity (ρ), also known as specific resistance, is a fundamental property of materials that characterises their ability to resist the flow of electric current.
Mathematical Formulation of Resistivity:
Resistance of a conductor is directly proportional to its length:
Resistance of a conductor is inversely proportional to its cross-sectional area:
By combining the relations for length and area dependence, we get:
Rearranging the equation:
Where,
R is the opposition offered by a conductor to the flow of electric current. It is measured in ohms (Ω).
ρ (rho) represents a constant called the "resistivity" of the material within the conductor. This property is sometimes referred to as "specific resistance." Resistivity is unique to each material and remains relatively constant under normal conditions.
l is the physical length of the conductor through which current flows. It is measured in metres (m).
A is the area perpendicular to the direction of current flow. It is measured in square metres (m^{2}).
Unit of Resistivity:
The SI unit of resistivity is the ohm-metre (Ω·m), often written as ρ = Ω·m.
This unit is derived by substituting the units of resistance (ohms), cross-sectional area (square metres), and length (metres) into the formula.
Materials and Their Resistivities:
Temperature Dependency:
The Significance of Resistivity:
Explore about Magnetic Effects of Electric Current |
In electrical circuits, the current flowing through a circuit is not only influenced by the potential difference (voltage) but also by the resistance present in the circuit. To achieve the desired current in circuits used in devices like radios, televisions, and similar appliances, it's often necessary to combine multiple resistances. These combinations can be made in two primary ways: (i) in series, or (ii) in parallel.
When you connect resistors in series, it means that they are arranged one after the other along the same path for the electric current to flow through.
When two or more resistances are connected between the same two points, they are said to be connected in parallel because they form parallel paths for the current to flow.
When designing electric circuits for domestic purposes, it's important to choose between series and parallel configurations based on the specific needs of the application.
Series circuits are suitable for decorative lighting, such as stringing hundreds or thousands of electric bulbs.
Advantages of Series Circuits for Domestic Wiring:
Disadvantages of Series Circuits for Domestic Wiring:
Parallel circuits are widely used in domestic wiring for lighting, appliances, and outlets.
Advantages of Parallel Circuits for Domestic Wiring:
Disadvantages of Parallel Circuits for Domestic Wiring:
Electric power is the rate at which electrical energy is used or consumed in an electrical circuit. It is measured in watts (W) and represents the rate of doing work or the rate of energy transfer within the circuit. Electric power is a crucial concept in understanding and analysing electrical circuits and devices. It is denoted by the symbol P. The formula for electric power is defined as:
Where:
P represents electric power.
W stands for the work done by the electric current.
t represents the time taken for the work to be completed.
Unit of Power: The unit of power is the watt (W), which is derived from the standard units of work (joule) and time (second). Therefore, 1 watt is equivalent to the consumption of 1 joule of energy in 1 second:
In practical applications, particularly for larger systems and appliances, the kilowatt (kW) is frequently used.
1 kilowatt (1 kW) = 1000 watts
We know that
the amount of work (W) performed by an electric current (I) as it flows through a circuit for a duration (t) under the influence of a potential difference (V) can be expressed as follows:
Putting this value of W in equation (1), we get:
Where:
P is the electric power in watts (W).
V is the potential difference (voltage) across the device or circuit in volts (V).
I is the current flowing through the device or circuit in amperes (A).
In other words, the power in watts is equal to the product of the voltage (in volts) and the current (in amperes).
In addition to the basic formula P = V × I, there are two more formulae for calculating electric power, which are particularly useful when you have information about voltage, current, and resistance. These formulae are derived from Ohm's law:
1. Power (P) in terms of Current (I) and Resistance (R):
Power can be can expressed using the equation:
P = V × I ... (1)
From Ohm’s law we know,
V/I = R
or V = I × R
Putting this value of V in equation (1), we get :
P = I × R × I
P = I2 × R
This formula shows that power is directly proportional to both the square of the current and the resistance. If either the current or the resistance increases, the power also increases significantly.
2. Power (P) in terms of Voltage (V) and Resistance (R):
We know that :
P = V × I ... (1)
From Ohm’s law we have,
V/I = R
or I = V/R
Putting this value of I in equation (1), we get :
P = V x V/R
P = V2/R
In this formula, power is directly proportional to the square of the voltage but inversely proportional to resistance. If the voltage increases, the power increases significantly, but if the resistance increases, the power decreases significantly.
Electrical energy is the energy consumed or used by an electrical device or appliance over a period of time. It is a measure of the total work done or the total amount of energy transferred in an electrical circuit. Electrical energy is commonly measured in units such as watt-hours (Wh) and kilowatt-hours (kWh).
The formula for calculating electrical energy (E) is given by the product of the power (P) of the electrical device or appliance and the time (t) for which it is used:
E = P × t
Where:
E is the electrical energy in watt-hours (Wh) or kilowatt-hours (kWh).
P is the power rating of the electrical device in watts (W) or kilowatts (kW).
t is the time in hours (h) for which the device is operated.
This formula allows us to calculate the total electrical energy consumed by an appliance when we know its power rating and the time it operates.
Units of Electrical Energy:
The heating effect of current is a phenomenon where electric current flowing through a conductor with resistance generates heat. This effect is widely used in various electrical appliances, such as electric heaters, stoves, toasters, and incandescent light bulbs. The heat produced is the result of the conversion of electrical energy into thermal energy.
Joule's Law of Heating: Joule's law of heating describes the relationship between the heat produced (H), the current (I) passing through a resistor, the resistance (R) of the resistor, and the time (t) for which the current flows. The formula for Joule's law of heating is:
H = I^{2} x R x t
Where:
H is the heat produced in joules (J).
I is the current in amperes (A).
R is the resistance in ohms (Ω).
t is the time in seconds (s).
The heat produced (H) is directly proportional to the square of the current (I^{2}), resistance (R) and the time (t) for which the current flows.
The heating effect of electric current has several important applications in our daily lives. Here are some notable applications:
Learn more about Sources of Energy |
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