Magnetism (11) Flashcards
Magnets produce _____________ fields
Magnetic
A magnetic field is a region where magnetic materials experience a __________
Force
Magnetic field lines are used to show the ________ and ____________ of magnetic fields
Size Direction
Magnetic field lines always point from _________ to __________
North South
Placing the north and south poles of 2 permanent bar magnets near each other creates a uniform __________ between the 2 magnets
Field
Like poles repel each other and opposite poles __________
Attract
When a magnet is brought near a magnetic material then the material acts as a __________. This magnetism has been ___________ by the original magnet.
Magnet Induced
The closer the magnet and the magnetic material get, the ___________ the induced magnetism will be
Stronger
Far from the magnet - __________ induced magnetism
Little magnetism induced
A current-carrying wire creates a _______________ field
Magnetic
An electric current in a material produces a _____________ field around it
Magnetic
The larger the electric current, the ___________ the magnetic field
Stronger
The direction of the magnetic field depends on the direction of the ___________
Current
What is the magnetic field around a straight wire
Concentric circles with the wire in the centre … right hand grip rule: Hold your right hand in such a way that your thumb points in the direction of the current, the curl of your finger will points in the direction of the magnetic field.
What is the magnetic field around a flat circular coil
The magnetic field is similar to that of a bar magnet. Concentric ellipses of magnetic field lines around the coil
What is the magnetic field inside a current-carrying solenoid like
Strong and uniform
What is the magnetic field outside a current-carrying solenoid like
Just like the one around a bar magnet
The ends of a ____________ act like the north and south pole of a bar magnet. This type of magnet is called an ________________________
Solenoid Electromagnet
When is a magnetic material considered soft
If it loses its induced magnetism quickly
When is a magnetic material considered hard
If it keeps its induced magnetism permanently
How can you increase the strength of the magnetic field around a solenoid
By adding a magnetically ‘soft’ iron core though the middle of the core`
How do 2 magnetic fields cause a current-carrying wire to move
When a current-carrying wire is put between magnetic fields, the 2 magnetic fields affect each other. The result is a force on the wire causing the wire to move.
Why do 2 magnetic fields cause a current-carrying wire to move
Because charge particles moving through a magnetic field will experience a force, as long as they’re not moving parallel to the lines
To experience the full force, the wire has to be _____ to the magnetic field
90°
If the wire runs __________ the magnetic field, it won’t experience any force at all. At angles between, it’ll feel …
Along
Some force
The force always acts in the _________ direction relative to the magnetic field of the magnets
Same
What is a good way of showing the direction of the force
To apply a current to a set of rails inside a horseshoe magnet. A bar is placed on the rails, which completes the circuit. This generates a force which rolls the bar along the rails.
The magnitude (strength) of the force ____________ with the strength of the magnetic field
Increases
The force _____________ with the amount of current passing through the conductor
Increases
Reversing which 2 things can reverse the direction of the force
The current or the magnetic field
Fleming’s left hand rule: What does the thumb represent
Force/Motion
Fleming’s left hand rule: What does the first finger represent
Magnetic field
Fleming’s left hand rule: What does the second finger represent
Current
4 factors which speed up an electric motor:
More current
More turns on the coil
Stronger magnetic field
A soft iron core in the coil
What does the split-ring commuter do
It swaps the contacts every half turn to keep the motor rotating in the same direction
How can the direction of an electric motor be reversed
By swapping the polarity of the d.c. supply OR by swapping the magnetic poles over
How can you work out which way the coil will turn
By using fleming’s left hand rule
Uses of an electric motor
Electric bell
Crane
What is electromagnetic induction
The creation of voltage in a wire which is experiencing a change in magnetic field
What is the dynamo effect
Using electromagnetic induction to transform kinetic energy into electrical energy.
What are the 2 different situations where you get electromagnetic induction
An electric conductor moves through a magnetic field.
The magnetic field through an electrical conductor changes
How can you test for electromagnetic induction
By connecting an ammeter to a conductor and moving the conductor througha magnetic field. The ammeter will show the the magnitude and direction of the induced current.
Dynamo effect: If the direction of movement is reversed, then the induced voltage/current will be _____________
Reversed
Dynamo effect: To get a bigger voltage, what 3 things can you increase
The strength of the magnet
The number of turns on the coil
The speed of movement
In an electric motor - you’ve got a current in the wire and a magnetic field which causes ______________.
In a generator it works the opposite way round - you’ve got a magnetic field and movement which induces a _____________.
Movement
Current
Generators rotate a coil in a ____________ field. Their construction is pretty much like a ________.
Magnetic
Motor
A.C. Generators: As the coil spins, a _________ is induced in the coil. This current changes ____________ every half turn. Instead of a split-ring commutator, A.C generators have ______ _______ and ____________ so the contacts don’t ________ every half turn. This means they produce a.c. voltage, shown by ______ displays
Current
Direction
Slip rings
Brushes
Swap
CRO
Power stations use A.C generators to produce _______________
Electricity
Transformers only work with an _________________ current
Alternating
Transformers change the size of the ____________ of an alternating current
Voltage
All transformers have 2 coils, the primary and the secondary, joined with an _______ core
Iron
When an alternating voltage is applied across the primary coil, the magnetically soft (iron) core ______________ and ____________________ quickly. This induces an alternating _____________ in the ______________coil
Magnetises
Demagnetises
Voltage
Secondary
What does a step-up transformer do? They have more turns on the _____________ coil than the _____________ coil.
Step the voltage up.
Secondary.
Primary.
What does a step-down transformer do? They have more turns on the _____________ coil than the _____________ coil.
Step the voltage down.
Primary.
Secondary.
The transformer equation:
What does p stand for in the transformer equation:
Primary
What does s stand for in the transformer equation:
Secondary
What does V stand for in the transformer equation:
Voltage
What does N stand for in the transformer equation:
Number of turns
Transformers are nearly 100% ______________
Efficient
What is the word formula for power supplied
Power = Voltage x Current
You can rewrite input power = output power as:
Vp x Ip = Vs x Is
(Primary voltage x Primary current = Secondary voltage x secondary current)
Transformers make transmitting mains electricity more ______________
Efficient
Step-up and step-down transformers are used when transmitting _________________ across the country
Electricity
The _____________ produced by power stations is too low to be transmitted efficiently. Power = VI, so the lower the voltage the __________ the current. A step-_____ transformer is used to boost the voltage before it is transmitted. Step-_______ transformers are used at the end of the journey to ________the voltage so it’s more useful and safer to use.
Voltage
Higher
Step-up
Step-down
Reduce
