Chapter 20 - Magnetism Flashcards
All metals can be attracted by magnet. T/F, why?
False, not all metals are magnetic material
What are 2 common examples of magnetic material
Steel, Iron
What are 4 common examples of non-magnetic material
Copper, glass, wood, rubber
Where is the position of a magnet that has the strongest attraction and weakest attraction respectively
Poles
Center
A the north pole of a freely suspended magnet will always point at ?
North direction of the earth
Law of magnetism
Like poles repel, unlike poles attract
How to test a material if it is a magnet?
Hang a permanent magnet, allow it to suspend freely.
Bring the material close to the two poles of the magnet, if the material REPEL the magnet, the material is a magnet. IF there are only attraction, the material is a magnetic material, not a magnet.
When a magnetic material is attract to a magnet, it becomes a _______ ?
Induced Magnet
What are the three ways to magnetise a magnetic material to a magnet?
Heating and hammering method
Stroking Method
Using a electric current
Describe the heating and hammering method for magnetisation
Place the magnetic material in a NORTH-SOUTH direction
Heat it to a very high temperature
Hammer it during the cooling process
Describe the stroking method (refer to the notes) for magnetisation
okay
Describe the electric current method for magnetisation
How to identify the north-pole for this method?
Place the magnetic material in a coil of wire (called solenoid) in North-South direction and passing a direct current through it
Use the right hand grip rule, place your fingers of your right hand (except for the thumb) to follow the current flow, the direction that your thumb pointed to is the North pole.
What are the two methods for demagnetisation?
By heating and hammering
Using an electric current
Describe the heating and hammering method for demagnetisation
Place the magnetic material in EAST-WEST direction
Heat the magnetic material at a very high temperature
Hammer it vigorously during the cooling process
Describe the electric current method for demagnetisation
Place the magnetic material in a coil of wire (Solenoid) in East-West direction and passing a Alternating Current (A.C Current) through it. When the CURRENT IS FLOWING, WITHDRAW the magnet from the solenoid.
What are the 3 differences between magnetisation and demagnetisation using the electric current method
Material in North-South. Material in East-West
Material dont withdraw, Material withdraw
Material in D.C current, Material in A.C current
Using the domain theory, explain what outcome these methods for magnetsiation and demagnisation achieved. Or before magnetisation or demagnetisation happens, what must happen or change first?
The methods all alter/ align the alignments of the domains
Explain using domain theory, why a material is magnetised
Explain using domain theory, why a material is not a magnetised
The domains of the material are all pointed to the same direction, the magnetic strength is the maximum, thus is magnetised
The domains of the material are all pointed to different directions, the magnetic strength is the minimum, thus is not magnetised
Why magnets will become weaker after sometime if you leave it alone?
The “free” poles at the end of the magnet will repel one another, altering the alignment of the domains
How magnet is usually stored so to prevent from losing magnetism?
Magnets are usually stored in pairs with two soft iron keepers across the ends of the magnets. In this way, the poles of the magnets will form a complete loop with no “free” poles, thus preventing them from repelling one another
Definition of a magnetic field
A region surrounding a magnet, in which a body of magnetic material will experience a MAGNETIC force
What are the two methods used to determine the magnetic field pattern for a bar magnet?
Iron filling method
Plotting compass method
Describe the iron filling method used to determine the magnetic field pattern of a bar magnet
State the disadvantage of the method
Place a magnet on a card
Sprinkle the iron filling on the card
Tap the card a little
Iron fillings will form a pattern which is the magnetic field pattern of the magnet
No direction of the field lines shown
Describe the plotting compass method used to determine the magnetic field pattern of a bar magnet
Place the compass from one end of the magnet to the other end of the magnet in a semicircle shape.
The needle of the compasses will form a semicircle shape which represent the pattern of the magnetic field line of the magnet. The head of the needle represents the direction of the magnetic field
Interaction of magnetic field lines (Refer to notes)
okay
Effect of magnetic materials on magnetic field (Refer to notes)
okay
A Bar magnet is placed near a iron bar, forming a T shape, how would the iron bar affect the field lines
The magnetic field line will enter the middle of the iron bar and come out from the two ends of the iron bar. An magnetic material has an effect of concentrating the field line by forcing it to pass through the magnetic material.
What are the 4 magnetic property differences between iron and steel
Easy to magnetised, Hard to magnetised
Loses magnetism easily, Retain magnetism longer
Used as electromagnet, Use as permanent magnet
What are the two methods that can increase the strength of electromagnet
Increase the number of the coils
Increase the current (Use higher voltage batteries)
Two use of electromagnet
electric bell
circuit breaker
Three use of permanent magnet
compass
electric door catches
loudspeaker
