Topic 13- Electromagnetic induction + Flashcards
How to produce a current in a wire?
-Move it within a magnetic field
-Cuases a potential difference
-Cuases electron flow
How to produce current on a small scale?
1) Spin a coil of wire between two permenant magnets
2)Produces small current so use a sensative ammeter (only miliamps produced)
How to produce current on a larger scale?
1)Steam produced (combustion of fossil fuels, heat water)
2)Steam pressured to turn turbines
3) Turbine connected to wire ciruit (generator)
4) Wire circuit is turned within the permenantt magnets
How to increase the Current/ Volatage?
-More coils
-Stronger magnet
-Speed up rotation
How to change direction of current?
-change polarilty
-Change direction of spins
How does an alternator work?
1) Both sides of the coil connected to a diff slip ring commutator
2) Placed in a magnetic field which induces a potential difference
3) Results in a force
4) Circuit moves in one direction
5) The commutator swaps the direction of movement every half turn
6) Cuases an alternating (AC) current
How does a dynamo work?
1) Coils are attached to a split ring commutator
2) Placed inside a uniform magnet to induce a potential difference
3) Results in a current and a force
4) Circuit moves in direction
5) Every half turn the commutator sides swap, switching the coild connection
6) Cuaseing current to only flow in one direction (DC)
How to make a generator more powerful?
-Used curveed magnets
-Will always be moveing parallel to the field lines
-Always at strongest
How does a microphone work?
1) Variations in sound vibrations cuase the diaphram to move more/less
2) Attached to a coil which moves over a stationary magnet
3) This variation in movement cuases a variation in current produced
How does a speaker work?
1) AC current is supplied to a cone with a coil wrapped around its end
2) AC current supplied cuases the wire to be induced to have a magnetic field
3) This interacts with the magnets magnetic field, cuaseing the cone to move
4) The variation in the AC current (back and forth movements) changes the sound waves produced
How does a transformer work?
1) Wire is coiled around an iron core (on both sides, diff number of coild)
2) AC is supplied to the wire, cuasing a change in current and thus change in magnetic field
3) Iron core is induced to produce its own magnetic field
4) Change in magnetic field cuases iron’s magnetic field to change
5) Change in irons magnetic field induces the other coil’s magnetic field and thus its current
How does a step up transformer work?
-Has more turns in its secondary coil
-Increases alternating voltage
-(decreases current as P=IV)
Why do we need step up transformers?
-Increase voltage and decrease current
-Current cuases the heating effect
-Cuases resistence decreases the current and thus the power
-Reduces heat loss so more efficient
this is bad over the long distance it travels
How do step down transformers work?
-Fewer turns in the secondary coil
-Increase the current (decreases the alternating potential difference)
Why do we need step down transformers?
-High voltage is unsafe for domestic use
What equation links number of coils and voltage?
Secondary coils/ Secondary voltage =
Primary coils/ Primary voltage
No.1/V1= No.2/V2
What is the structure of the national grid?
-Power station
-Step up transformer
-National grid
-Step down transformer
-Domestic use
What equation links potential difference and current with transformers?
with 100% efficiency
Primary coil (Pd) x Primary coil (C) =
Secondary coil (Pd) x Secondary coil (C)
VxI=VxI
What equations show usefulness of transformers?
-P=E/t
-P=IV
-P= (I^2)R (power loss due to resistence)
-VI(2)=VI(1)
-VNo.1=VNO.2
1)Show that increasing the voltage decreases the current for constant power
2)Decreasing current significantly decreases power loss
3)Transformers change the current for voltage
4)More efficient
