Class 10 Science • Complete Detailed Notes
Electric current is the rate of flow of electric charge through a conductor.
The SI unit of electric current is ampere (A). One ampere means that one coulomb of charge passes through a cross-section of a conductor in one second.
An electric circuit is a continuous conducting path through which electric current can flow.
Potential difference between two points is the work done per unit charge to move a charge from one point to another.
The SI unit of potential difference is volt (V).
A voltmeter is used to measure potential difference between two points. It is connected in parallel with the component across which potential difference is to be measured.
An ammeter is an instrument used to measure electric current in a circuit.
Ohm's law states that, at constant temperature, the potential difference across a conductor is directly proportional to the current flowing through it.
For an ohmic conductor under constant physical conditions, the V-I graph is a straight line passing through the origin.
Resistance depends on various physical factors.
For the same material and cross-sectional area, resistance increases with length.
For the same material and length, resistance decreases when the cross-sectional area increases.
Resistivity is a property of a material that indicates how strongly the material resists electric current.
Different materials have different resistivities. Conductors generally have low resistivity while insulating materials have much higher resistivity.
When resistors are connected end-to-end so that the same current passes through each resistor, they are said to be connected in series.
When several resistors are connected between the same two points, they are connected in parallel.
When electric current passes through a resistance, electrical energy can be converted into heat energy.
This is called the heating effect of electric current.
According to Joule's law, the heat produced in a resistor is proportional to the square of current, resistance and time for which current flows.
Therefore:
Electric power is the rate at which electrical energy is consumed or converted.
The SI unit of power is watt (W).
Electrical energy consumed by an appliance is given by:
In household electricity billing, energy is commonly measured in kilowatt-hour (kWh).
Electrical appliances in homes are generally connected in parallel so that each appliance receives the required potential difference and can operate independently.
A fuse is a safety device used to protect an electrical circuit from excessive current.
When excessive current flows, the fuse wire becomes hot and melts, breaking the circuit.
Overloading occurs when too many appliances are connected to a circuit or when the circuit is made to carry current greater than its safe capacity.
Excessive current can cause heating of wires and may become a fire hazard.
A short circuit occurs when a very low-resistance path is created between points of significantly different potential, causing a large current to flow.
Fuses and other protective devices help disconnect the circuit under unsafe current conditions.