Electricity
Electric Current and Circuits
- Electric Current: It is the amount of charge flowing through an area in unit time or it is the rate of flow of electric charges.
- Electric current is the flow of electrons from one end to another. Direction of electric current is taken opposite to the direction of flow of electrons.
- If is the net charge that flows across the cross section of a conductor in time , then Current through the cross section is
- SI unit of electric charge is coulomb (C).
- SI unit of electric current is Ampere (A)
- Ammeter is an instrument used to measure the electric current in a circuit.
Electric Potential and Potential difference
- Flow of charges (movement of electrons) will happen if there is a difference of electric pressure which is also known as potential difference along the conductor. Potential difference can be produced by a battery. Potential difference across the terminals of battery is occurred through the chemical reactions inside the battery.
- When we connect the conductor with terminals of battery, this potential difference makes the charges in motion and produce electric current. So potential difference between two points = Work done (W)/ Charge (Q), V= W/Q.
- SI unit of electric potential difference is volt (V)
- Potential difference is measured using the instrument called voltmeter. Voltmeter is connected parallel across the points between potential difference is to be measured.
Circuit Diagram
- Circuit diagram is the schematic representation of electric circuit, in which components of circuits are represented by symbols. Given below is the symbols of commonly used components in circuit diagram.
Ohm’s Law
- Ohm’s law states that the potential difference V across the metallic wire in an electric circuit is directly proportional to the current flowing through it, provided it’s temperature remains the same.
- Here R is the Resistance and it’s the ability of the conductor to resist the flow of charges through it. SI unit of resistance is Ohm and represented using the symbol
.
- Current through a resistor is inversely proportional to its resistance. Which means if we increase the resistance the current flow will decrease.
- Various types of resistors
- A variable resistor is a type of resistor whose electrical resistance value can be adjusted.
- Fixed Value Resistors: It is a type of resistor whose electrical resistance value is fixed.
- Rheostat is device which is used to change the resistance in the circuit.
Factors on which the resistance of a conductor depends
- Resistance of a conductor depends on
- Length of the conductor
- Area of cross section of the conductor
- Nature of the material
- Resistance is directly proportional to its length (l), and inversely proportional to the area of cross section (A)
Resistance of a system of resistors
Resistors in series
- When resistors are connected one after other, as shown in the figure, we can say the resistors are in series.
- When resistors are connected in series, the total resistance (Effective resistance) increases.
- The effective resistance can be found by simply taking sum of all resistance in series. The effective resistance can be found by using the formula.
- Current flowing through each resistor in series is the same. Voltage drop will be there across each resistor connected in series. Such that voltage across each resistor will be different. Larger resistance will have a larger voltage drop across it, while a smaller resistance will have a smaller voltage drop across it.
Resistors in parallel
- From the above figure it is clear that ends of all resistors are connected to common points. Here one end of all resistors is connected to one common point A and other to a common point B. The potential drop across each resistor is the same. In parallel circuit, total current is being divided among each branch.
- Effective resistance of parallel circuit can be found using the equation:
Heating Effect of Electric Current
- Heating devices mostly consists of resistors. These resistors resist the flow of electric current. As a result, Electrical Energy does some work to overcome the resistance. We studied in the law of conservation of energy that the energy can neither be created nor destroyed. It can be converted from one form to another. Here electrical energy is converted to heat energy.
- For this conversion, some work is to be done by electrical energy. SI unit of work or energy is Joules. One joule of work is required to move one coulomb of charge under one-volt potential difference.
- Work done
- One must use certain amount of energy to do work and we call it as Power. So Electric power of a device is the energy consumed by an appliance in unit time. The unit of power is watt.
- Devices that make of heating effect of electric current are
- Electric heater
- Electric fuse
- Electric iron
- Electric oven
- Joule’s Law: The heat generated( H) in a circuit carrying current is the product of square of current(I) in the conductor, the resistance of conductor(R) and the time for which current flows (t) in the circuit.
Important formulas
Electric Power
- The amount of energy consumed by an electrical appliance in unit time is its power. The unit of power Watt (W)
