8_Consequences_STUDENTS.pptx

Physics 8 Consequen ces Pg. 156-177 Magnetism Pg. 156-177 Magnetic field around a wire Magnetic field around a wire 1) What is the strength of the field? 2) What is the shape of the magnetic lines? 3) Where is the magnetic field stronger? 4) W...

Physics 8 Consequen ces Pg. 156-177 Magnetism Pg. 156-177 Magnetic field around a wire Magnetic field around a wire 1) What is the strength of the field? 2) What is the shape of the magnetic lines? 3) Where is the magnetic field stronger? 4) What happen to the magnetic field strength if the current is increased? 5) What is the direction of the magnetic field considering the current of the circuit? Magnetic field around a wire 1) Current produces a weak magnetic field 2) Magnetic lines are circles 3) Field is stronger closer to the wire 4) Increasing the current increases the strength of the field 5) The direction of the magnetic field produced by the current is the same as the flow of the electrons  When a current flow Current out of the page in the wire the compasses allign with the magnetic field of the wire in a circle shape What is the direction of the curr Magnetic field around a COIL (solenoid)  Magnetic field around a coil The current 1) What produce a is the strength ofstronger the field? magnetic field 2)The 2) How canisthe longer magnetic the solenoid field (long coli)of thethe coil be stronger increased? is the magnetic field produced 3) The 3) How does the coil field electromagnetic magnetic producedfield looksalike? is similar magnet magnetic field 4) 4) What happenthe Increasing to the magnetic current field the increase strength if theof strength current is the field increased? 5) 5) What is the direction The direction of the of the magnetic magnetic field N field (from considering the to S) produced current of the circuit? by the current is the same as the flow of the electrons 6) Reversing theto What happen current reverses the direction of the thedirection magnetic of field the magnetic if the field the current is reversed?  Electromagnets What is it? A magnet created by using a current that magnetises a magnetic material such as iron, creating a temporary magnet  Electromagnets What is its utility? Its magnetic effects can be switch on and off How does an Electromagnet Work? https://www.youtube.com/watch?v=cxELqN7wjS0 Electromagnets investigation Aim: investigate the strength of an electromagnet depending on its number of turns Number of turns Electromagnet Material: strength/g 1x digital scale + cable 10 1x electric power supply + cable 20 2 x crocodile wires 30 2 x wires 40 2 x stands (blue base) 50 2 x masses (100g and 10g) 60 1 x 5m red wire 70 1x clamp 80 1x clamp holder 90 1 x tape 100 Pg. 156-16 Magnetic force on a current What happens when a copper wire is placed in a magnetic field of a magnet? Because copper is not magnetic, it does not feels any force from the magnet What happens when a copper wire is placed in a magnetic field of a magnet when a current pass through it? There is a force on the wire produced by the magnet and the re passing through a magnet When a wire move inside a magentic field in a perpendicular way compare to the magnetic field S N lines, a force (F) is produced The force would point downwards if either the magnetic filed or the current were reversed  How can the force be increased? 1) The current is increased 2) A stronger magnet is used 3) The length of the wire inside the magnetic field is increased (more turns added)  Direction of the force (Fleming’ s left-hand -Whatrule) is the direction of the magnetic field lines? - From the N-pole to the S-pole - What is the direction of the conventional current - From the positive (+) to the negative (-) terminal of the battery REMEMBER: The Fleming’ s left- hand rule only works when the current and the field directions are at right What angles happen to the force if they have the same direction? There is no force Turning effect on a coil DC Motor, How it works? https://www.youtube.com/watch?v=LAtPHANEfQo Turning effect on a coil 1) What is the direction of the flow of the current in the coil? The current flows in opposite direction along the two sides of the coil Turning effect on a coil 2) What is the direction of the force in the coil? According to the Fleming’s left-hand rule one side is pushed up and the other opposite side in pushed down producing a turning effect of a coil Turning effect on a coil 3) How can we increase the turning effect? Adding more turns on the coil Increase the current Increase the size of the magnet Turning effect on a coil Practical: make the motors following the instructions from the learning sheet given Practical motors don’t need to memorise Use several coils set at different angle The coil made of hundreds of turns of wire are wounded on a core (armature) which become magnetised The magnet increasing the poles are curved to create a radial magnetic strength field thatof the magnetic makes field the turning effect at its maximum Electromagnet are sometimes preferable to permanent magnet so that a a.c. can be used, which, by keep changing direction, force the electromagnet to do the same. This makes the turning effect to be always the same, and the motor to rotate normally Electromagnetic induction https://www.youtube.com/watch?v=tC6E9J925pY https://phet.colorado.edu/sims/html/faradays-law/latest/ faradays-law_en.html The induced voltage in a conductor (wire) is proportional to the rate at which magnetic fields lines are cut by the conductor  Electromagnetic induction The induced voltage in a conductor (wire) is proportional to the rate at which magnetic fields lines are cut by  Electromagnetic induction Can a magnetic field be used to produce a current? Yes, when a wire is moved across a magnetic field a small voltage is generated in the wire (electromagnetic induction) Is this effect detectable with an instrument? Yes, using a galvanometer, an instrument sensitive to very small currents, where its pointer moves to the left or right depending on the direction of the current  Electromagnetic induction How can the induced voltage be increased? 1) moving the wire faster 2) By using a stronger magnet 3) By increasing the length of the wire in the field  Electromagnetic induction How can the direction of the induced voltage be reversed? 1) Moving the wire in opposite direction 2) Turning the magnet around reversing the filed lines What happen if the wire is not moving or is moving parallel to the filed lines? No induced voltage or current is generated because no field lines are cut  Electromagnetic induction Is there another way to create an induced current? Yes, if a magnet is pushed into a coil, a voltage is induced in the coil. The result is the same because the filed lines are cut  Electromagnetic induction How can the direction of the induced voltage be reversed? 1) Pulling out the magnet from the coil 2) If the S-pole instead the N-pole of the magnet is pushed inside the coil What happen if the magnet is not moving? No induced voltage or current is generated because no field lines are cut  Electromagnetic induction Practical demonstration 1) Electromagnetic induction creates a weak voltage using a single wire that cut the magnetic fields lines of a strong magnet 2) Electromagnetic induction creates a stronger voltage using more wires that cut the magnetic fields lines of the strong magnet 3) The induced voltage is increased when the wires are moved faster  Electromagnetic induction Practical demonstration 4) Moving the wire in opposite direction reverse the current 5) If the wire are not moving or move in the direction of the field lines no current is produced  Electromagnetic induction Practical demonstration 6) Electromagnetic induction creates a weak voltage using a magnet that is pushed into a coil 7) The induced voltage is increased when the magnet is are moved faster or 8) the number of coils is increased 9) Moving the magnet forward and backward (in opposite direction) reverse the current 10) If the magnet is not moving no current Pg. 157-16 Generators 1) What is their utility? (Think of a dynamo) Produce electricity 2) How do they produce a voltage that makes a current to flows? Use electromagnetic induction 3) What do you call a generator when generate a.c.? Alternators Each side of the coil travel upwards and downwards repeatedly through the magnetic field, producing a current that repeatedly flows backwards and forwards (a.c.) Which type of current is produced? A.c. or d.c.? Why?  Positions of the rotating coil through the magnet magnetic field N S Graph Graph of the generator’s a.c. output How can the voltage be increased? 1) Increasing the number of turns in the coil (area of the coil) 3) Using a stronger magnet 4) Rotating the coil faster Generators can produce a d.c. using a commutator that reverse the connections to the outside circuit every half-turn. When the coil rotate produce a.c. but the action of the commutator make the current in the outside circuit to flow in the same direction. D.c. generator 3= the main power supply is more dangerous Because it is not as stable as the direct current/b Around 300 V F= 1/time F= 1/0.02 F= 50 hz Pg. 162-16  Coil and transformers Fleming’s right-hand rule is used when motion causes a current Right hand rule What do you notice it is different than usual??? Lenz’s law (induced current direction): An induced current always flows in the direction such that it OPPOSES the change which produced it  An electromagnet is used to produce a current into another coil through induction Show the This effect is Faraday_en simulation and similar to a pushing a demonstration magnet toward Generator here the coil very must be alternative. fast 1) How The coil can of thethe No electricity with a direct generator electromagnet voltage in the goes second inside coil the be second increased? coil 2) Increasing the This effect is called mutual number of turns of the induction second coil Application of mutual induction using set up transformer (Outpu (Inpu t) t) How can the current in the secondary output be increased? Increasing the number of turns in the secondary coil  Output voltage (V2) = turns on output coil (n2) Input voltage (V1) turns on input coil (n1) x/100= 20/5 X= 4x100 V=? X= 400 V V= ? A=? 400 Because the output coil has four times the number of coils of the input coil, the output voltage is four times the input voltage Input voltage (V1) x Input current (I1) = Output voltage (V2) x Output current (I2) Power is the same/ wats are the same Because you cannot create or destroy energy. Therefore need to find out how much you need to multiply voltage Get the initial power from primary side V=? 400 A=? A==? 2.5 V ==?? W 1000 Voltage x current (power) is the same in both sides of a transformer Step-up transformers More turns in the output coil than on the input coil to produce more voltage in the output coil. Used in power stations to increase the voltage of overhead power lines Step-down transformers Fewer turns in the output coil than on the input coil to produce less voltage in the output coil. Used in batteryV=charges, ? computers, to reduce the `voltage A of the = ? is needed a.c. mains because lower level for other circuits. Step up and step down transformers Step up= more turns in the output coil than on the input coil to produce more voltage in the output coil. Used in power stations to increase the voltage in power lines Step down= fewer turns in the output coil than on the input coil to produce less voltage in the output coil. Used in batterry charges, computers, to reduce the voltage of the a.c. mainw because lower level is needed for other circuits  240/6= 40 8000/40= 200 Stays the same because the power doesn’t change as you cannot destroy initial power Stays the same because the power doesn’t change as you cannot destroy initial power Pg. 167-16 Slide answers page 61 1a) step down transformer since we initially have more turns, then they are lowered in the secondary 1b) 100/20= 5, 30/5= 6V 2a) 500 and 150 should be sued 2b)largest= 2000= 2000/100= 20 x 3= 60v, smallest= 100/2000= 0,05x 3= 0,15V 2c) no movement there fore no change in magnetic field, thereofre no voltage I induced/created  Transformers in action When energy has to be sent over long distances it is advantageous to send it at very high voltages. This is because transmitting at high voltages and low currents helps to reduce the energy lost in the power transmission lines that are used in the grid. Stepping up the voltage by a factor of 10 reduces the current by a factor of 10 and therefore reduces the power lost during transmission by a factor of 100 (i.e. 102). This is an important saving for electricity supply companies (and their customers!). Transformers play a crucial role in increasing WAVES Pg. 169-174  Do you notice something wrong in this video? Longitudinal waves compression rarefaction Longitudinal waves  How does sound travel? During its passage, soundair pushes ___ particl _________ forwards backwar es and _________, longitudinal ds creating ____________ waves  Which physical phenomenon makes sound? Demo: Look at this tuning fork. How does it  Which physical phenomenon makes sound? Vibrations. Feel your throat when you speak. What do you notice? What is sound? It is a form of ______that changesenergy from the kineticcaused by _______energy vibrations ___________ , traveling in the formlongitudin wave of ____________ al_____ s Can you hear a sound without a medium like air, solids or liquids? Demo: a bell in a vacuum  Can you hear sound in this situation? Diffraction If so, what is the effect that allow sound to be heard through gaps and round obstacles? The speed of sound What do you notice in this video?  How fast is sound in air? A person is filming a storm, and he is 1214,4 km from it. He sees a lightning, and he can hear the thunder after 3.68 seconds. Speed = distance time Speed = 1214.4 m = 330 m/s 3.68 s The speed of sound is 340 m/s. If the thunder is heard 20 s after the lighting, how far is the storm in km? 340 x 20= 6800= 6.8km What is the formula to calculate speed (v) from frequency and wavelength? 0.6 m/s 1/5= 0,2 m 330/660= 0,5 m 3x108 m/s  What is the range of sound frequencies we can hear? Range that us humans can hear= 20hz- 20000hz Do different animals ear the same frequencies?  It is important for authors to reference sources so that the reader trusts that the sources come form a reliable source. And that none of the information is false. Also due to copyright reasons and plagarism chicken human 10-8500HZ 55-8000HZ 50-12000HZ human chicken human Pg. 169-171 Wavelenght= 1500/2,500000= 0,0006 meters= 6 x 10 -4 Time= d/velocity= 3/100= 0,03/1500= 0,00002 = = 2 x 10-5 x2= 4x10-5 How does our hearing system work? How a loudspeaker works? Interaction – Assessments Formative assessment Question pg. 175-177