Brief Intro on Magnets Magnetic material- is a type of material that can be magnetized and is attracted to other magnets.Strong metals contain1- iron They are called2- nickel “Ferromagnetics”3- cobalt Iron and alloys of iron are called ferrous. (Ferrous in Latin means iron) Aluminium, copper, and other non-magnets are called non- ferrous.
Properties of magnets:• Have a magnetic field around them• Has two poles exerting forces on other magnets. – Like poles repel – Unlike poles attract• Attract magnetic materials by inducing magnetism in them.
What is induced magnetism?Some metals like iron and steel are attracted to othermagnets because if there is a magnet near by, theythemselves get magnetized. Magnetism is INDUCED inthem.– When steel is pulled away from a magnet, it keeps its induced magnetism causing it to become a permanent magnet.(hard magnet)– When iron is pulled away from a magnet, it looses its induced magnetism meaning that iron was only a temporary magnet.(soft magnet)
Magnetic Effects of Current• When an electric current is passed through a wire an magnetic field is produced. The features of this magnetic field are: – They are circles – Field is strongest close to the wire – Increasing current increases strength of field.
Right-hand grip rule
Electromagnets• These are types of magnets that can be switched on and off. CoilsIron coreThe strength of the magnetic field can be increased by: - Increasing the current. - Increasing the number of turns in the coil
Magnetic Relay Metal contacts.• When electricity is passed through the coil end wires, it induced a magnetic field in the iron ROD. This attracts the iron STRIP causing both metal
Circuit Breaker Circuit breaker- it is an automatic switch cutting off the current within a circuit if it rises above a specified value. - In the case on the left, the pull of the electromagnet has become so strong that it has attracted the soft iron armature. This causes the contacts to open and stop the current. - If u press the reset button, the contacts close once again.
Magnetic force on the current• Copper is a non- magnet feels no force of the magnetBut..• If it has a current passing through it, there will obviously be a force on the wire.The wire moves ACROSS Force is increased if: the field. It is not -Current is increased attracted to it. -Stronger magnet is used -Length of wire in field is increased.
Flemings Left Hand Rule
Electric motors An electric motor transfers electrical energy to kinetic energy.• A motor is made up from a coil of wire which is positioned between the two poles of the magnet.• When the current flows through the coil, it creates a magnetic field. This magnetic field that is produced interacts with the magnetic field produced by the 2 permanent magnets.• The combination of these two magnetic fields exert a force, pushing the wire at right angles to the permanent magnetic Improve turning effect
Increasing Turning Effect• Increase the current• Use a stronger magnet• Increase the number of turns on the coil• Increase the area of the coil.
Electromagnetic Induction • A magnetic field can be used to produce current.When the wire is moved across themagnetic field a small EMF(voltage) iscreated. This is called electromagneticinduction.“EMF is induced”Induced EMF increased by:-Moving wire faster-Using stronger magnet-Increasing length of wire.
Induced CurrentsFleming’s right hand rule: Difference between the left hand and the right hand rule: -When current causes motion the left hand rule applies -When motion causes current the right hand rule applies
Generators• The coil rotates• Magnetic fields are cut• EMF is generated• Causes current to flow• Coil rotates– Increasing EMF: upwards, downwards, u- Increasing the number of pwards causing the turns on coil current to flow - Increasing area of coil backwards, forwards, ba Use stronger magnet - - Rotate coil faster ckwards.
Coils and Transformers• Moving magnet induces EMF• Magnetic field SAME effect.• Mutual induction: when coils are magnetically linked so that changing current in one coil causes and induced EMF in the other.
Simple Transformer - Alternating current flows through primary coil - This sets up an altering magnetic field in the core. - Coils of the secondary coil ‘cut’ the altering magnetic field thusoutput voltage Turns in output coil inducing an alternating = voltage in the output coil. Input voltage Turns on input coil
Step-up and Step-down transformersStep-up: this is when thenumber of output coils isgreater than the numberof input coils which meansthat there will be a greateroutput voltage as opposedto input voltage. Step-down: this is when the number of output coils is less than the number of input coils which means that there will be less output voltage as opposed to input voltage.
Power Through a TransformerInput x Input = Output x Outputvoltage current voltage current
SummaryTransformers:Current + Motion=Magnetic FieldElectromagnetic Induction:Magnetic Field + Motion = CurrentGenerator (Electric Motor):Current + Magnetic Field = Motion
Important electronic components1. Resistors – keep currents + voltages at levels desired by the electronic component2. Capacitor – store small amounts of electric charge3. Diodes – allow the current to flow in only one direction4. Light-emitting diodes (LED) – glow when a small current is passed through them.
Continued…5. Transistors – used to amplify signals6. Integrated circuits(micro-chips)– contain complete circuits with : a) Resistors b) Transistors c) Other components7. Relays– electromagnetic switches.
Diodes• Can be used to change AC to DC Rectification• Lets forward parts of the AC through but blocks the backwards part.• Forming a DC Input 1 Output resister
Potential Divider• A potential divider only delivers a portion of the voltage.
Reed Switch• A reed switch is operated by a magnetic field.
Transistors as switches• It is a Collector semiconductor device made of silicon. Base Emitter
The NPN resistor 1000 ohms c 6V b e• In the diagram above there are actually two circuits put together as one. The first circuit is the one with the base and the emitter ( input circuit) and the second is the circuit with the collector and the emitter (output circuit).1. Two input connections joined together no current flow2. Input the base greater than 0.6Vlamp switches on3. 1000 ohm resister is present to protect the input to the resistor, allowing input to be higher than 0.6V to 5V without harming transistor.4. Little current is needed in the input circuit.
Thermionic Emission• Basically what happens in thermionic emission is that the tungsten filament is heated to 2000 degrees Celsius. Some electrons that are hot enough escape the surface of the white hot surface. These then pass through the vacuum and on the screeen.
The Oscilloscope• The Cathode Ray Oscilloscope uses (as mentioned on previous slide) an electron gun and the X and Y plates to adjust where the stream of electrons go.• The X-Plates move the beam horizontally (Left or Right)• The Y-Plates move the beam vertically (Up or Down)
• The Y-plates are connected to a Y input terminal. These are connected to an AC supply.Examples of things that use electron beams:- Television- X-ray tube
Alpha Alpha particles are made of 2 protons and 2 neutrons. This means that they have a charge of +2, and a mass of 4. Alpha particles are relatively slow and heavy. They have a low penetrating power - you can stop them with just a sheet of paper. Because they have a large charge, alpha particles ionise other atoms strongly
Beta•Beta particles have a charge ofminus 1, and a mass of about1/2000th of a proton. .•They are fast, and light.•Beta particles have a mediumpenetrating power - they arestopped by a sheet of aluminum•Beta particles ionize atoms thatthey pass, but not as strongly asalpha particles do.
Gamma •Gamma rays are waves, not particles. This means that they have no mass and no charge. •Gamma rays have a high penetrating power - it takes a thick sheet of metal such as lead, or concrete to reduce them significantly. •Gamma rays do not directly ionize other atoms •We dont find pure gamma sources - gamma rays are emitted alongside alpha or beta particles. Strictly speaking, gamma emission isnt radioactive decay because it doesnt change the state of the nucleus, it just carries away some energy.
In a Magnetic Field
What is Background Radiation?• Background radiation comes from naturally decaying substances such as soil, rocks, air, food and drink.• It is detected by a Geiger Muller Tube
Radioactive decay- Alpha Decay
Radioactive decay- Beta Decay
Half-Life• This is the amount of time taken for the nuclei of a radioactive substance to decay.
Nuclear FusionThis does not take place on Earth so far. It is the process that powers the stars.
What can Radioactivity be used for?1. Tracers2. Radiotherapy3. Testing for cracks4. Thickness monitoring5. Carbon Dating- after an organism dies the amount of C-14 inside it begins to decay. It can be used to find out how old a substance is.6. Dating Rocks
This is the physics syllabus Complete Best of luck for your IGCSE exams Especially my fellow candidates of May/June 2011!!!