- 1 Electricity
- 1.1 Electricity and a few Terminologies
- 1.2 Electric Current and Electric Circuit
- 1.3 Measurement of Electric Current
- 1.4 Electric Potential and Potential Difference
- 1.5 Measurement of Potential Difference
- 1.6 Electric Circuit Symbols
- 1.7 OHM’s Law
- 1.8 Factors on which Resistance Depends
- 1.9 Resistors in Series
- 1.10 Resistors in Parallel
- 1.11 Heating effect of Current
- 1.12 Applications of Heating Effect of Current
- 1.13 Electric Power
- 1.14 SCIENCE Revision Notes
Electricity and a few Terminologies
- Electrical appliances convert the electricity directly into heat, light or motion whereas electronic appliances have micro-chips that take electricity and convert it into endless useful things (display picture on TV, play songs on radio etc.) and not just simple heat, light or motion.
- When electric charge flows through a conductor (like a metallic wire), it is said that the conductor has electric current.
- Electric current, generated by cells or batteries inside a torch, makes the torch glow.
- A switch is a conducting path between cells and the bulb. An ON switch makes the bulb glow whereas an OFF switch puts it in non-glowing state.
- An electric circuit is a complete and continuous path for electric current. Current does not flow when the path is broken. A switch makes and breaks the circuit inside a torch.
Electric Current and Electric Circuit
- Until the discovery of electrons, the electric current was considered to be a flow of positive charge and the direction was considered from positive terminal of the battery to the negative terminal.
- In reality, electric current is flow of negatively charges particles called electrons. These flow from negative terminal of the battery to the positive terminal.
- As a convention, the direction of current is taken opposite to the direction of flow of electrons.
Measurement of Electric Current
- SI Unit of electric charge is Coulomb (C).Charge is usually denoted by letter Q.
- SI Unit of electric current is Ampere (A).Current is usually denoted by letter I.
Electric Potential and Potential Difference
- A battery or a cell has a potential difference due to reaction of chemicals inside it even when it is not connected to any circuit. Once connected, the potential difference makes the electrons flow and the current is generated in the circuit/conductor. A battery generates this potential difference till the chemicals inside it are not completely spent.
- Potential difference is also defined as work done to move a unit charge from one point to another.
Measurement of Potential Difference
- SI unit of electric potential difference is Volt (V).
- SI unit of Work done is Joule (J).
Electric Circuit Symbols
Factors on which Resistance Depends
- ρ is called electrical resistivity of the material of the conductor. SI unit is Ωm.
- Resistivity of conductors is very low whereas the insulators have a very high resistivity.
- Resistivity varies with Temperature.
- Alloys having higher resistivity than metals are used in electrical heating devices, like iron and toasters, tungsten is used in filament of electric bulbs and copper and aluminium are used for electrical transmission lines.
Resistors in Series
- The current through the circuit remains the same.
- The potential difference becomes sum of the individual potential difference across each resistor.
- Equivalent resistance of the circuit is the sum of individual resistances.
- Two different electrical appliances, having different current requirements, cannot be connected in series as the current is constant in a series circuit.
- If one of the components fails in a series circuit, the circuit gets broken and none of the other components get the current.
Resistors in Parallel
- The current through the circuit is the sum of currents through each branch of the circuit.
- The potential difference across the two points of the circuit remains the same.
- The reciprocal of equivalent resistance of the circuit is the sum of reciprocal of the individual resistances.
- Parallel arrangement divides current in different branches and hence each component receives the required amount of current.
- If one of the components fails in the parallel circuit, the rest work as usual.
Heating effect of Current
- Loss of energy in the unwanted heat.
- Wear and tear of components.
Applications of Heating Effect of Current
- Appliances based on Joule’s heating are electric iron, electric toaster, electric heater, oven etc.
- Heating effect produces light in a bulb. Tungsten wire inside the bulb becomes hot and emits light when current passes through it. Since it has a high melting point of 3380°C, it does not break. Also, due to the presence of gases like chemically inactive nitrogen and argon inside the bulb, the filament remains thermally isolated and its life increases.
- Joule’s heating is also used in fuses where a thin wire protects the household appliances from power surge. Fuse wires are made of thin aluminium, copper etc. with an appropriate melting point. These wires melt and break the circuit due to heating during excessive current.
- SI unit of Power is Watt (W).
- 1 Watt power is consumed when 1 Ampere of current flows through a device at a potential difference of 1 Volt.
- Electrical energy is the amount of work done or energy consumed in a given amount of time. So, it is measured in Joules or Wh (watt hour) or most commonly as kWh (Kilowatt hour).
- 1 kWh = 3.6 x 10 Joule (J).
SCIENCE Revision Notes
Chapter:01 Chemical Reaction & Equation
Chapter:02 Acid Base & Salt
Chapter:03 Metals & Non Metals
Chapter:04 Carbon & its Components
Chapter:05 Periodic Classification of Elements
Chapter:06 Life Processes
Chapter:07 Control & Coordinates
Chapter:08 How do Organisms Reproduce
Chapter:09 Heridity & Evolution
Chapter:10 Light Reflection Refraction
Chapter:11 The Human Eye & the Colourful World
Chapter:13 Magnetic Effect of Electric Current
Chapter:14 Source Of Energy
Chapter:15 Our Environment
Chapter:16 Management of Natural Resource