P4- Magnets Flashcards
Define a magnet
A material or object which produces a magnetic field
What must all magnets have
A north and a south pole and are surrounded by a magnetic field
How do you represent magnetic feilds
By using field lines
Which directions must field lines point
From the north pole to the south pole
How can you show where a magnetic field is strongest
By the denisty of the lines
How do you show a strong magnetic field in a diagram
Using densly packed field lines
What can you use to determin the north and south pole of a magnet
Using a compass
What are the difference between permanent
and induced magnets
Periminate magnets have there own magnetic fields but induced magnets become a magnet when they are placed in a magnetic feild
What are the 3 naturally magnetic elements
-iron (Fe)
-cobalt (Co)
-nickel (Ni)
What is the motor effect
A wire carrying a current creates a magnetic field. This can interact with another magnetic field, causing a force that pushes the wire at right angles
What hand do you use to work out the direction of current
Left hand
When using flemings left hand rule what does your thumb represent
The direction of the force
When using flemings left hand rule what does your fore finger represent
The direction of the magnetic field
When using flemings left hand rule what does your middle finger represent
The direction of the current
How do you arrange you fingers in flemings left hand rule
All at 90 degrees to one another
What does a split ring commutator do
Switches the postive and negitve connections every half turn
Why is a split ring commutator used
It makes it so that the forces are always acting in the same direction which makes the coil turn the full 360 degrees
How can you increase the speed of the rotation in an electric motor
- Increase the currents
- Add more coil
- Use stronger magnets
What can the generator effect also be refered to as
Electromagnetic induction
What happens when you move a wire coil through a magnetic feild
It induces a potenial difference in a wire
What happens to a coil when you stop moving it through a magneitc field
The potential differnce dissapears
What causes the potenial difference in a wire in a magnetic feild
The change in the magnetic field is what induces a potential difference
What happens when you change the direction of the wires movements in a magnetic feild
The direction of the potential difference changes each time in changes direction
What happens when you move the coil wire along the mangetic field ( back and forth)
No potential difference or current will be induced because there is no change in magnetic field
What happens when you close coil when it is moving through a magnetic field
A poteinial difference and a current is induced
How do you increase the size of the potential difference in a coil moving through a magnetic field
- Stronger magnets
- Move the magnets faster
- Shape the wire into a proper coil
How does using stronger magnets increase the potenial difference
Stronger magnets=
Stronger magnetic field= Bigger potential difference
How does moving the magnetic faster increase the potenial difference
Faster movements =
Faster magnetic field will change =
Bigger potential difference
How does shaping the wire into a coil increase the potenial difference
More turns in the wire =
Bigger poteinal difference
Define a solenoid
A solenoid consists of a wire coiled up into a spiral shape. When an electric current flows, the shape of the magnetic field is very similar to the field of a bar magnet
What is the magnetic field strength of a solenoid
Strong and uniform.
What are generators
Devices generate electricity from rotational motion
What are ‘Alternators’ and ‘dynamos’
Different types of generators
How do Dynamos create electricty
They use a split ring comunitator in an electric motor
How do Alternators create electrcity
They use slip rings and brushed in an electric motor
What type of current do Dynamos produce
Direct current
(d.c)
What type of current do Alternators produce
Alternating current
(a.c)
How do slip rings and brushes work
Slip rings maintain constant contact with the same sides of the coil.
What happens to the current in an Alternator as the coil rotates faster
(terms of a graph)
The peaks and occalations of the current on a graph get larger
Define an induced magnet
Any object that can be influenced by magnetic fields, and has the potenial to become a magnet
What are the commen magetic materials
- Nickle
-Cobalt
-Iron
-Alloys of the 3 (steel….)
Are induced magets perminant
No they are only magnets temporarly when in a magnetic field
How do create an induced magnet
Place a piece of magnetic material(which wasnt actually a magnet) into the feild of a magnet. This induces its own magnetic field.
Which type of force will there always be between induced and perminate magnet
The force will allways be attractive- North to south
What materials are magnetically soft
- Nickle
- Iron
Define Magnetically Soft
A material that loses its magnetism quickly when taken out of a magnetic field
Define Magnetically Hard
A material that loses its magetism slowly after being removed from a magnetic field
What materials are Magnetically hard
- Steel
What happens when you pass a current through a wire
A magnetic field is induced
What does the right hand rule show you
The direction of a mangetic field in a wire
How do you use the right hand rule
Curl your hand into a fist and point your thumb in the direction of the current . The direction your fingers are curled in is the direciton of the current.
What shape is the magentic field lines on a wire
Concentric circles
What shape are the magentic field lines in a circlular coil
Elipses and a line straight through the middle
What is the magnetic field of a soleniod simialar to
It is similar to the magnetic field of a bar magent
Which way do the arrows point in a magnetic field diagram of a solenoid
From North to South
What is a solenoid also known as
An ElectroMagnet
What happens when you stop the current through an Electrogmagnet
The magentic field stops
How do you reverse the direction of the magentic field in an Electromagnet
Reverse the direction of the current
How do you increase the strength of an electromagnet
- Increase the current in the solenoid
- Increase the no. of turns (keep lenght the same)
- Decrease the lenght of the coil (keep turns no. the same)
- Add a soft iron core
How does the denisty of the turns in a solenoid effect the mangnets strength
Densly packed coils have a strong magentic field and less densly packed coils have a weaker magnetic field strength
How does adding a soft iron core effect the solenoids strength as a magnet
As iron is a soft magnetic material it will become an induced magnet when the solenoid is switched on which increases the magnetic field. It will also lose its magnetic field when the current is switched off
Define the motor effect
A current carrying wire in the presence of a magnetic field will experience a force
What is the eqaution for force experienced by a wire (during the motor effect
Force = current x magnetic field strenght x length of wire
What is another phrase for magnetic field strength
Magnetic flux density
What is the magnetic field strength mesured in
Teslas (T)
What is an oscilloscope
A volt meter that shows how voltage varries over time
What does the oscilloscope graph of an alternator look like
As the current switches direction the oscillations are on both the positve and negitive sides of the graph
What happens to an oscilloscope graph of an generator when the coil rotates faster
The oscillations get larger and more frequent
What does the oscilloscope graph of an dynamo look like
As the current is always flowing in the same direction the oscillations always stay on either the positvie or negitve sides of the graph
What the role of a transformer
To increase of decrease the voltage
What are transformers used for in the real world
To increase the volatage of electricty made in power stations so they can be transported around the country and to decreace the voltage when it reaches homes
What is a step up transformer
A transformer that increases the voltage decreases the current
What is a step down transformer
A transformer that decreases the voltage increases the current
What are the parts of a transformer
A primary coil
A secondry coil
An iron core
What is the coil ratio in a step up transformer
The primary coil has less turns that the secondry coil
What is the coil ratio in a step down transformer
The primary coil has more turns than the secondry coil
What type of current must be used in a transformer
An alternating current
How do transformers work
- When supplied with an alternating current, the primary coil will generate a magnetic field
- This then induces an alternating magnetic field in the iron core
- This induces an alternating voltage in the secondry coil which (if the circit is complete) leads to an alternating current in the secondry coil
The ratio of turns in the primary and secondry coil affects…
The current and voltage in the secondry coil
What are the wires in transformers covered in
They are insulated in plastic
