Electricity Class 10 Science Physics Notes
Electricity forms the backbone of modern technology. It explores the nature of electric charges and their motion. This chapter introduces fundamental concepts that are important to understand. Some important concepts include electric circuits, including electric current, potential difference, Ohm's law, resistance, and the practical applications of the heating effect of electric current.
Electric Current and Potential Difference
The phenomenon of electricity arises from the existence and flow of electric charge. There are two types of charges: positive and negative. Like charges repel each other, while unlike charges attract. The smallest independent unit of charge is the charge on an electron (e).
- SI Unit of Charge: Coulomb (C).
- Fundamental Charge: 1e = –1.6 × 10⁻¹⁹ C
Electric Current (I) is defined as the rate of flow of electric charge through any cross-section of a conductor. Conventionally, the direction of electric current is taken as the direction of flow of positive charge, which is opposite to the direction of flow of electrons (e⁻).
Formula for Electric Current: I = Q / t
Electric Potential and Potential Difference (P.D.)
For current to flow in a conductor, there must be a difference in electric pressure between the two ends, which is provided by a cell or a battery. This difference is called the Potential Difference (V).
Potential Difference between two points in an electric circuit is the amount of work done (W) in moving a unit positive charge (1 C) from one point to the other.
Formula for Potential Difference: V = W / Q
This also means the work done is W = Q × V
SI Unit of Potential Difference: Volt (V).
Resistance, Resistivity, and Ohm's Law
Ohm's Law describes the relationship between the current (I) flowing in a metallic conductor and the potential difference (V) across its ends. The law states that the potential difference (V) across the ends of a metallic conductor is directly proportional to the current (I) flowing through it, provided its temperature remains the same (constant).
Mathematical Form of Ohm's Law:
V ∝ I
V = I × R
Where R is a constant called the Resistance of the conductor.
Combination of Resistors and Heating Effect of Current
Resistors in a circuit can be connected in series or parallel. In a series connection, the same current flows through all resistors, and the total resistance equals the sum of individual resistances (Rₑq = R₁ + R₂ + R₃). This setup gives higher resistance. In a parallel connection, all resistors share the same voltage, but the current divides among them. The equivalent resistance is given by 1/Rₑq = 1/R₁ + 1/R₂ + 1/R₃, resulting in lower resistance than any single resistor.
Heating Effect of Electric Current (Joule's Law)
When an electric current flows through a conductor, the conductor becomes hot. This is known as the heating effect of electric current. This effect is due to the work done by the source to maintain the current; this energy is dissipated as heat.
Joule's Law of Heating states that the heat produced (H) in a resistor is:
- Directly proportional to the square of the current (H ∝ I²).
- Directly proportional to the resistance of the conductor (H ∝ R).
- Directly proportional to the time for which the current flows (H ∝ t).
Joule's Law Formula:
H = I² × R × t
Where H is the heat produced (in Joules), I is the current (in Amperes), R is the resistance (in Ohms), and t is the time (in seconds).
Heaing Effect Applications
This effect is utilized in heating devices like electric heaters, electric irons, toasters, and, importantly, in the electric fuse. An electric fuse is a safety device that prevents damage to circuits and appliances by melting when the current exceeds a safe limit
