Magnets & Circuits

Magnets & Circuits

1. Properties Of Magnets

   • On a magnetic like poles repel each other and opposite poles attract
   • When a bar magnet is suspended freely, it always comes to rest in a north-south direction where the north pole on the magnet faces to the north pole on the Earth
   • The stronger the poles the larger the attractive or repulsive force, also the closer the magnets are, the greater the force is
   • Magnets attract ferrous materials such as Iron, Steel, Nickel, Cobalt

2. Properties of Iron and Steel differences

   • Iron is very soft and is used as a temporary magnet (electromagnet)
   • Steel is much harder than Iron so it is used as a permanent magnet (Bar magnet)

3. Diodes and relays

   • Diodes are used in a circuit to make the current flow in one direction only. It is a polarised component with two leads, called a cathode and an anode
   • If the anode is connected to a higher voltage than the cathode then the current will flow from the anode to the cathode this forward bias, and if the cathode has the higher voltage then the diode will not conduct electricity this is reverse bias.
   • A relay is a coil which becomes an electromagnet when a current flows through it, the magnet then repels or attracts a switch which can complete or break a circuit

4. Thermistors and Light dependant resistors (LDR)

   • At low temperatures the resistance of a thermistor is high and little current flows through, and when temperature is high the resistance is low so more current flows through
   • In the dark the resistance of an LDR is high so a less current flows through it and in high light levels the resistance is low and more current flows through it ( e.g Security lights)

5. Electrical Insulators and Conductors

   • Conductors allow electricity to pass through them e.g Metals
   • Insulators don't allow electricity to pass through them e.g Plastic and Polythene
   • Semi-conductors have conducting and insulating properties, the way the material is connected to a power supply determines if it allows or prevents a current to flow through it e.g Silicon

6. Equations

   • V = I x R
   • E = I x V x T
   • P = I x V
   • Q = I x T
   • E = P x T
   • E = Q x V

7. Ferrous and Non-Ferrous materials

   • Ferrous materials mostly contain iron and also have other metals or elements in them to give the required properties, they are magnetic and give little resistance to corrosion e.g Iron and Steel
   • Non-Ferrous materials don't contain iron, are not magnetic and show more resistance to corrosion than ferrous materials e.g Aluminium, Zinc and Copper etc

8. Capacitors

   • Capacitors are used to store energy, the amount of charge it can store is measured in farads and it consists of two conducting plates separated by an insulator to prevent the electricity flowing all the way round the circuit
   • When a discharged capacitor is connected to a circuit it will start to charge, when a conductor (e.g Light bulb) is connected the capacitor will discharge. The electrons flow from negative plate to positive one

9. Fuses, Circuit Breakers and Earth Wires

   • Fuses are used to break circuits, the fuse melts when the current exceeds the fuse level and gets too high
   • Circuit breakers don't need to be replaced and can easily be reset. A spring loaded push switch is held in position by a spring loaded iron bolt, an electromagnet is positioned to pull the bolt away from the switch if the current gets to high
   • The earth wire connects the case of an appliance, if the live wire touches the case then the earth wire will conduct the electricity away to stop electrocution

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