P7 keywords and mixed definitions.doc Download this file
Tuesday, 28 February 2012
Thursday, 9 February 2012
6.18
6.18
· 6.18 explain the use of step-up and step-down transformers in the large-scale generation and transmission of electrical energy
· http://youtu.be/LZKhGGBcYFI
6.20
· 6.20 recall and use the relationship (for 100% efficiency): input power = output power Vp Ip = Vs Is 
6.17
· 6.17 recall the structure of a transformer, and understand that a transformer changes the size of an alternating voltage by having different numbers of turns on the input and output sides
6.17 Practical - model answers · If you…
· Turn the powerpack to dc No current is induced in the Secondary Coil. To induce current you need a changing magnetic field and this is not produced by applying dc to the Primary Coil
· Turn the powerpack to ac ac is induced in the Secondary Coil. To induce current you need a changing magnetic field and this is produced by applying ac to the Primary Coil
3. Increase the number of turns in the Secondary Coil The size of the induced voltage in the secondary coils increases
4. Increase the voltage on the Primary Coil The size of the induced voltage in the secondary coils increases
5. Decrease the number of turns in the Secondary Coil The size of the induced voltage in the secondary coils decreases
6. Decrease the voltage on the Primary Coil The size of the induced voltage in the secondary coils decreases
6.17 Practical - model answers · If you…
· Turn the powerpack to dc No current is induced in the Secondary Coil. To induce current you need a changing magnetic field and this is not produced by applying dc to the Primary Coil
· Turn the powerpack to ac ac is induced in the Secondary Coil. To induce current you need a changing magnetic field and this is produced by applying ac to the Primary Coil
3. Increase the number of turns in the Secondary Coil The size of the induced voltage in the secondary coils increases
4. Increase the voltage on the Primary Coil The size of the induced voltage in the secondary coils increases
5. Decrease the number of turns in the Secondary Coil The size of the induced voltage in the secondary coils decreases
6. Decrease the voltage on the Primary Coil The size of the induced voltage in the secondary coils decreases
6.19
· 6.19 recall and use the relationship between input (primary) and output (secondary) voltages and the turns ratio for a transformer:
input (primary) voltage = primary turns output (secondary) voltage secondary turns Vp/Vs = np/ns6.16
· 6.16 describe the generation of electricity by the rotation of a magnet within a coil of wire and of a coil of wire within a magnetic field; also describe the factors which affect the size of the induced voltage
· Magnet rotating near coil · Coil rotating near magnet · ac generator
6.16 Practical - model answers
· Connect a hand turned generator to a light bulb. Observe the light bulb when you...
· Rotate the generator slowly The induced voltage decreases
· Rotate the generator quickly The induced voltage increases
3. Increase the strength of the magnet The induced voltage increases
4. Increase the number of turns in the coil The induced voltage increases 6.16 Plenary 17 January 2012 15:20
· What are the 3 ways that you can increase the size of the current induced in a generator? Answers
· Increase the strength of the magnets
· Increase the speed of the relative motion
· Use a coil with more turns of wire
· Magnet rotating near coil · Coil rotating near magnet · ac generator
6.16 Practical - model answers
· Connect a hand turned generator to a light bulb. Observe the light bulb when you...
· Rotate the generator slowly The induced voltage decreases
· Rotate the generator quickly The induced voltage increases
3. Increase the strength of the magnet The induced voltage increases
4. Increase the number of turns in the coil The induced voltage increases 6.16 Plenary 17 January 2012 15:20
· What are the 3 ways that you can increase the size of the current induced in a generator? Answers
· Increase the strength of the magnets
· Increase the speed of the relative motion
· Use a coil with more turns of wire
6.15
· What’s the motor effect?
· "If there’s a magnetic field perpendicular to a current in a wire, the wire moves in a direction perpendicular to the field and the current" (FLHR)
· So what about if we move a wire in a magnetic field? What happens in the wire?
>
· When we move a wire in a magnetic field, a current is induced in the wire 6.15
· 6.15 recall that a voltage is induced in a conductor or a coil when it moves through a magnetic field or when a magnetic field changes through it; also recall the factors which affect the size of the induced voltage
6.15 Practical - model answers
· If you...
· Push the North pole of the magnet into the coil A negative current flow shown by a negative deflection on the ammeter
· Keep the magnet stationary within the coil No current
3. Pull the North pole of the magnet out of the coil A positive current
4. Push the South pole of the magnet into the coil A positive current
5. Push the North pole of the magnet slowly into the coil A smaller negative current
6. Push the North pole of the magnet quickly into the coil A larger negative current
7. Change the coil for one with more turns of wire and push the North pole of the magnet into the coil A larger negative current
8. Push the North pole of a neodymium (strong) magnet into the coil A larger negative current
9. Move the magnet in and out of the coil repeatedly. What sort of current is this? An alternating current 6.15 Plenary answers 16 January 2012
· Explain carefully how you can induce a current in a wire (3 marks)
· State 3 ways you can increase the size of this induced current (3 marks) Answers
· The wire must be perpendicular to a magnetic field
· The wire and magnetic field must move relative to each other – the wire must “cut” through the magnetic field lines/lines of magnetic flux as it moves
· A current is induced in the wire. The induced current is perpendicular to both the field and the motion
· Increase the strength of the magnets
· Increase the speed of the relative motion
· Use a coil of wire instead of a single piece of wire
· "If there’s a magnetic field perpendicular to a current in a wire, the wire moves in a direction perpendicular to the field and the current" (FLHR)
· So what about if we move a wire in a magnetic field? What happens in the wire?
>
· When we move a wire in a magnetic field, a current is induced in the wire 6.15
· 6.15 recall that a voltage is induced in a conductor or a coil when it moves through a magnetic field or when a magnetic field changes through it; also recall the factors which affect the size of the induced voltage
6.15 Practical - model answers
· If you...
· Push the North pole of the magnet into the coil A negative current flow shown by a negative deflection on the ammeter
· Keep the magnet stationary within the coil No current
3. Pull the North pole of the magnet out of the coil A positive current
4. Push the South pole of the magnet into the coil A positive current
5. Push the North pole of the magnet slowly into the coil A smaller negative current
6. Push the North pole of the magnet quickly into the coil A larger negative current
7. Change the coil for one with more turns of wire and push the North pole of the magnet into the coil A larger negative current
8. Push the North pole of a neodymium (strong) magnet into the coil A larger negative current
9. Move the magnet in and out of the coil repeatedly. What sort of current is this? An alternating current 6.15 Plenary answers 16 January 2012
· Explain carefully how you can induce a current in a wire (3 marks)
· State 3 ways you can increase the size of this induced current (3 marks) Answers
· The wire must be perpendicular to a magnetic field
· The wire and magnetic field must move relative to each other – the wire must “cut” through the magnetic field lines/lines of magnetic flux as it moves
· A current is induced in the wire. The induced current is perpendicular to both the field and the motion
· Increase the strength of the magnets
· Increase the speed of the relative motion
· Use a coil of wire instead of a single piece of wire
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