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
Tuesday, 31 January 2012
6.11 to 6.14 Plenary answers
6.11 to 6.14 Plenary answers
Why? Using FLHR
1. Magnetic Field is N to S (down the page) = First finger
2. Current is to the left = seCond finger
3. Motion is out of the page = ThuMb
6.11
· 6.11 appreciate that there is a force on a charged particle when it moves in a magnetic field as long as its motion is not parallel to the field
Solar wind creating aurora animation
Timelapse of aurora
6.14
· 6.14 recall that the force on a current-carrying conductor in a magnetic field increases with the strength of the field and with the current
Exam style question
· What changes can you make to a simple dc motor to increase the force it can exert? (3 marks)
Model Answer
· Increase the strength of the magnetic field
· Increase the current in the coil
· Increase the number of turns on the coil
6.12
· 6.12 recall that a force is exerted on a current-carrying wire in a magnetic field, and how this effect is applied in simple d.c. electric motors and loudspeakers
6.12 Practical - dc motor
· Connect a dc motor to a power pack
· How you can reverse the direction of spin of the motor? (2 ways)
· How you can make a stronger turning force on the motor? (2 ways)
3. How can you see that the turning force is stronger?
Answers
1.
a. Reverse the poles of the magnets
b. Reverse the direction of the current in the coil by switching over the polarity of the wires to the power pack
2.
a. Increase the current in the wire (by increasing the voltage of the power pack)
b. Increase the strength of the magnetic field (by adding more magnets to the yoke)
3. The motor spins faster which indicates a larger turning force
6.12 dc motor simulation
28 November 2011
15:06
Exam style question
· Explain carefully how an alternating current in the coil of a loudspeaker can create a sound (4 marks)
Gapfill Model Answer
· When a ______ flows __ the ____, it is p____________ to the magnetic field
· This creates a ______ on the coil, due to ___ _____ effect, and so the coil _____
· When the _________ current reverses ______, the direction of the _______ is also reversed and the coil moves in the ________ direction
· The moving ____ is attached to a ____ which also moves __________ and forwards.
· This makes ___ ________ vibrate and this is the _____ we can hear
Model Answer
Any four points from...
· When a current flows in the coil, it is perpendicular to the magnetic field
· This creates a force on the coil, due to the motor effect, and so the coil moves
· When the alternating current reverses direction, the direction of the force is also reversed and the coil moves in the opposite direction
· The moving coil is attached to a cone which also moves backwards and forwards.
· This makes air particles vibrate and this is the sound we can hear
6.13
Practical - the current balance
· Use a current balance to investigate what happens when a current flows in a magnetic field
· How many magnetic fields are created by this apparatus?
· How could you make the wire move further? (2 ways)
· How could you change the direction the wire moves in? (2 ways)
Answers
1. 2 magnetic fields:
a. the uniform magnetic field created between the poles of the permanent magnet
b. the magnetic field around the wire when the current flows
2.
a. Increase the current in the wire
b. Increase the strength of the magnetic field
3.
a. Reverse the poles of the magnets
b. Reverse the direction of the current
· 6.13 use the left hand rule to predict the direction of the resulting force when a wire carries a current perpendicular to a magnetic field
<<FLHR practice.pptm>>
6.13 FLHR simulation
28 November 2011
15:06
Website:
http://www.walter-fendt.de/ph14e/lorentzforce.htm
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Tuesday, 24 January 2012
Tuesday, 17 January 2012
Improvement Plan (Mocks)
Mark in Test: 84% (76/90)
IGCSE grade in test: A
Are you on target? T
Scientific facts:
1. Analogue signals continuously vary and have a range of values
2. Shiny surfaces are poor absorbers, good reflectors
3. The Earth wire provides a path of low resistance for the current
4. Friction causes charge due to the movement of electrons
5. Electrical energy is turned into thermal energy in a kettle
Can you improve your exam technique?
1. Read the question carefully!
How much revision did you do?
· 2 hours
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