ICSE Physics Class 7 Notes Chapter 7 Electricity and Magnetism
→ Some materials behave in a particular manner showing magnetic properties.
→ A freely suspended bar magnet always point in North-South direction.
→ Like poles repel each other while unlike poles attract each other.
→ Magnet is neutral at its centre and has maximum magnetic effects at its ends called the poles.
→ Poles always exist in pairs with opposite polarities and can never be isolated.
→ Examples of magnetic substances are iron, cobalt, nickel.
→ Examples of non-magnetic substances are wood, plastic aluminium, copper.
→ The poles are not exactly the ends of the magnet but they are slightly inside.
→ For a given magnet, both the poles are of equal strength.
→ Earth’s magnet has its south pole situated near the geographic north.
→ Electromagnets are the temporary magnets which are made up of soft iron core with a winding of insulated copper wire.
→ Freely suspended current carrying solenoid always rests in north-south direction.
→ A direct current source has the fixed positive and negative terminals, e.g. a battery.
→ Hans Christian Oersted discovered that if an electric current is passed through a conductor, a magnetic field is
developed around it.
→ The study of magnetic effects produced due to electric current is known as electromagnetism.
→ The direction of magnetic field due to a straight current carrying conductor is obtained by any of the following rules:
(a) Right Hand Thumb Rule.
(b) Right Hand Cork Screw Rule.
→ The property due to which a changing magnetic field within a closed conducting coil induces electric current in the coil is called electromagnetic induction.
→ The current produced in a closed coil when magnetic lines of force rapidly change within it is called the induced current.
→ The symbol for alternating current is –
→ The strength of induced current can be increased by increasing the –
(a) the number of turns in the coil
(b) strength of the magnet used
(c) relative speed between the magnet and closed coil.
→ We cannot think of modern life without electricity. We light our homes and other places of work with electricity.
→ It is used to run electric fans, televisions, geyser, electric irons, room heaters, refrigerators, music system etc.
→ Cell is a primary source of electricity. A combination of two or more cells is a battery.
→Some other sources of electricity are generator and solar cells.
→ The path along which an electric current flows is called a circuit.
→ Electricity has the following effects :
(a) Heating effect
(b) Magnetic effect
(c) Chemical effect
(d) Mechanical effect
→ When an electric path is complete is called closed circuit and the path with a break is called open circuit.
→ The substances which allow the electricity to flow through them are called conductors, e.g. metals, human body etc.
→ The substances which do not allow electricity to flow through them are called insulators, e.g. wood, paper, glass etc.
→ The consumption of electricity is calculated from the meter in kWh.
→ Electric fuse is a device which limits the current in an electric circuit.
→ All electrical appliances are connected in parallel in household circuits.
→ We should be cautious in using electricity.
→ Certain precautions should be taken before working on an electrical gadget or circuit.