- Electric energy from a cell is used to do work on charges, which is converted into heat in a resistor or other forms, like motion in a motor.
- The work done (energy) in moving a charge Q across a potential difference VAB is:
Work = VAB × Q - Heat produced (H) in a resistor over time t is given by Joule’s Law of Heating:
H = I2 × R × t - According to Ohm’s Law:
VAB = I × R - Electrical power (P) is the rate of energy transfer and is calculated as:
P = VAB × I
Its unit is watt (W), where 1W = 1 volt × 1 ampere.
Definitions [15]
Definition: Electric Circuit
A continuous and closed path of an electric current is called an electric circuit.
Define the following:
Semiconductors
Semiconductors: Substances whose resistance decreases with the increase in temperature are named as semiconductors. E.g. manganin, constantan etc.
Define an electric current.
An electric current is measured by the amount of electric charge moving per unit time at any point in the circuit.
The magnitude of an electric current is the number of electric charges flowing through a conductor in one second.
Define the following:
Electromotive force
Electromotive force: When no current is drawn from a cell, when the cell is in open circuit, the potential difference between the terminals of the cell is called its electromotive force (or e.m.f.).
Define the following:
Conventional current
The movement of the positive charge is called conventional current.
Define the unit of current.
The unit of electric current is ampere (A). When 1 C of charge flows through a conductor in 1 s, it called 1 ampere (A) current.
I = `Q/t`
Define the term resistivity.
The resistivity of a material is the resistance of a wire of that material of unit length and unit area of cross-section.
Define the following:
Super conductors
Substances whose resistance decreases tremendously with decreasing temperature and reaches nearly zero near absolute zero are called superconductors; e.g., lead, tin, etc.
Definition: Current
Current is defined as the rate of flow of charge.
Define the term potential difference.
The amount of work done in moving a unit positive charge from one point to another point in an electric field is called the potential difference.
Define the term current.
An electric current is a flow of electric charge. In electric circuits this charge is often carried by moving electrons in a wire.
Define the following:
Variable resistor
A variable resistor has a resistance that can be varied. It is used to vary the amount of current flowing in a circuit.
Define the following:
Fixed resistor
A fixed resistor has a resistance of a fixed value. Common types of fixed resistors include carbon film resistors and wire-wound resistors.
Define the term resistance.
Resistance is the obstacle that the wire presents to the current flow.
Definition: Resistance
The obstruction offered to the flow of current by the conductor (or wire) is called its resistance.
Formulae [1]
Formula: Resistance of Conductor
R ∝ \[\frac {1}{A}\]
or
R = ρ\[\frac {1}{A}\]
The SI unit of resistivity is Ω m.
Theorems and Laws [1]
State Ohm’s law.
At constant temperature, the current flowing through a conductor is directly proportional to the potential difference across its ends.
In formula form: V = IR
Where:
- V = Voltage (potential difference)
- I = Current
- R = Resistance
Key Points
Key Points: Electric Current
- Electricity is a convenient and controllable form of energy widely used in homes, industries, schools, and hospitals.
- Electric current is produced when electric charges flow through a conductor, and it flows only through a closed, continuous electric circuit.
- A switch completes or breaks the circuit; when the circuit is broken, current stops flowing, and devices like bulbs do not glow.
- Electric current is the rate of flow of charge, given by the relation I = Q / t, where Q is charge and t is time.
- In metallic wires, electrons are the charge carriers, but by convention, current flows from the positive to the negative terminal, in the opposite direction to electron flow.
Key Points: Electric Circuit
Key Points: Electric Resistance
- Free electrons in a metal move randomly; without a potential difference, there is no net flow of current.
- When a potential difference is applied, electrons drift towards the positive terminal, but collide with fixed positive ions, losing energy.
- These collisions cause resistance, and the number of collisions determines the amount of resistance in the conductor.
Concepts [12]
- Electric cell
- Electric Current
- Symbols and Functions of Various Components of an Electric Circuits
- Electric Circuit
- Types of Circuits: Simple Circuit
- Electrical Conduction in Solids
- Flow of Charges (Electrons) Between Conductor
- Direction of the Electric Current - Conventional and Electronic Flow
- Electric Resistance
- Factors of Resistance
- Conservation of Electrical Energy
- Social Initiatives for Energy
