- Heating Effect: Current through a resistor produces heat, calculated by H = I²Rt or H = VIt (Joule’s Law).
- Heat Applications: Used in devices like irons, heaters, bulbs, and fuses (to stop excess current).
- Power Unit: 1 kWh = 3.6 × 10⁶ J, called 1 unit of electrical energy in electricity bills.
- Short Circuit & Fuse: A short circuit causes a large current; the fuse wire melts to break the circuit and prevent fire.
- MCBs: Miniature Circuit Breakers automatically cut off power during overload or fault conditions.
Definitions [8]
Definition: Electrical Energy
When two dry bodies are rubbed together, they get charged due to the movement of free electrons from one body to the other body, so they possess electrical energy.
Define Electric power.
Electric power (P) is the rate at which electrical energy is transferred or consumed in an electrical circuit.
Definition: Electric Power
In an electrical circuit, electric power is defined as the rate at which electrical energy is supplied by the source.
Definition: Specific Resistance
Specific resistance of a material is the resistance of a wire of that material of unit length and unit area of cross section.
Definition: Conductivity
The reciprocal of specific resistance is known as conductivity.
Define fuse.
Electric fuse is a safety device which is used in household wiring and in many appliances.
Definition: Heating effect of electric current
When a resistor is connected in an electrical circuit, heat is produced in it due to the current. This is known as the heating effect of current.
Define the following:
Electrolyte
The solution through which the electricity passes is called an electrolyte.
Formulae [2]
Formula: Electric Power
Electric Power P = \[\frac {W}{t}\] = VI = \[\frac {V^2}{R}\] = I2R
Write the mathematical expression for Joule’s law of heating.
The mathematical expression of Joule’s Law of heating is: H = I2 Rt
Where,
H = Produced Heat
I = Current flowing through the device
t = Time taken
r = Resistance of the appliance
Key Points
Key Points: Electric Power
- Electrical power represents the rate at which electrical energy is supplied by the source in an electric circuit.
- The S.I. unit of electrical power is a watt (W), and larger units such as kilowatt, megawatt, and gigawatt are used for measuring higher power.
Key Points: Specific Resistance
- Specific resistance is a characteristic property of a substance and differs among metals, semiconductors, and insulators.
- Specific resistance depends on temperature: it increases with temperature for metals and decreases with temperature for semiconductors, while it remains nearly constant for some alloys.
- Specific resistance does not depend on the shape and size of the conductor and remains unchanged when a wire is stretched or doubled.
Key Points: Heating Effect of Electric Current
Concepts [15]
- Concept of Electric Currents in Conductors
- Drift of Electrons and the Origin of Resistivity
- Limitations of Ohm’s Law
- Resistivity of Various Materials
- Temperature Dependence of Resistance
- Forms of Energy > Electrical Energy
- Electrical Power
- A combination of resistors in both series and parallel
- Cells, Emf, Internal Resistance
- V-I Characteristics (Linear and Non-linear)
- Specific Resistance
- Resistivity of Various Materials
- Cells in Series
- Heating Effect of Electric Current
- Cells, Thermo e.m.f. Electrolysis
