Magnetism and Electromagnetism New Flashcards
laws of magnetism
-two like poles repel
-two opposite poles attract
name of force during attraction or repulsion from a magnet
magnetic force
characteristics of magnetically soft materials
-easy to magnetise
-easily lose their magnetism(temporarily magnetised)
characteristics of magnetically hard materials
-are difficult to magnetise
-do not easily lose their magnetism(permanently magnetised)
examples of magnetically soft and hard materials
soft: iron
hard: steel
magnetic field
the region around a magnet where a force acts on another magnet or on a magnetic material
what do magnetic field lines represent
direction and strength of a magnetic field
how is the strength and direction of a magnetic field shows
direction: arrows
strength: spacing of the magnetic field lines(close = strong)
rules when drawing magnetic field lines
-always go from north to south
-two magnetic field lines cannot touch or cross other field lines
where are magnets strongest at
at the poles
how does the strength of the magnet changed further away from the magnet
the magnetic field becomes weaker, shown by the field lines getting further apart
magnetic field lines of common positions
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when is a uniform magnetic field produced
gaps between opposite poles
what is a uniform magnetic field
magnetic field that has the same strength and direction at all points(equal spacing between all magnetic field lines)
what are magnetic materials
materials which are attract by magnets
magnetic materials
iron steel cobalt nickel
which pole will attract a magnetic material
both poles
how to test if a material it magnetic or a magnet
-if it can be repelled by a known magnet then the material is a magnet
-if it can only be attracted it is a magnetic material
types of magnets
permanent magnets
induced magnets
features of a permanent magnet
-produces its own magnetic field
-does not lose its magnetism
what is induced magnetism
when a magnetic material temporarily turns into a magnet when placed in a magnetic field
does an induced magnet have poles
yes, it has a north and south pole
how does the pole of a induced magnet form
the end of the material closest to the magnet will have the opposite pole to magnet’s pole closest to the material
what happens when an induced magnet is removed from the magnetic field
it will lose most/all of its magnetism easily
method to investigate magnetic fields
- place the magnetic on top of a price of paper, draw a dot at one end of the magnetic near its corner
- Place a plotting compass next to the dot, so that one end of the needle of the compass points away from the dot
3.Use a pencil to draw a new dot at the other side of the compass needle - Move the compass so that it points away from the new dot, and repeat the process above
- Keep repeating the previous process until there is a chain of dots going from one end of the magnet to the other
- Then remove the compass, and link the dots using a smooth curve – this will be the magnetic field line
- repeat several times to create several other magnetic field lines
what happens(magnetically) when current flows through a conducting wire
a magnetic field is produced around the wire
what evidence is there that the magnetic field from current has no poles
circular field pattern
what shape is the magnetic field produced due to current carrying wire
-concentric circles
right hand thumb rule
point your thumb in the direction of the current, then where the other fingers are pointing shows the direction of the magnetic field
what happens if you reverse the direction of current in a wire
it will reverse the direction of the magnetic field
what does increasing the current do(magnetically)
increases the strength of the magnetic field lines
motor effect
a wire with current flowing through it is placed in a magnetic field and experiences a force
how does the motor effect work
-two interacting magnetic fields, made from the current an the magnetic field the wire is placed in
-which causes the wire to experience a force
how does a dc motor work
-horizontal coil completes circuit with cell
-current flowing through coil produces magnetic field
-interacts with uniform external field, force is exerted on the wire
-forces acting in opposite direction(one up and one down) of each side of the coil cause it to rotate
-Fleming’s left hand rule shows it rotates
-once the coil rotates at a right angle, split ring is no longer in contact with the brushes, no current flowing; no forces act
-due to momentum of the coil, it continues to rotate
-split ring reconnects with brushes and current flows through coil
-coil is connected other way around electrically so the forces on the coil are in the same direction as before
-coil receives another turning force and continues to spin
factors affecting the speed of dc motor
-speed - increasing current increases the strength of the magnetic field
factors affecting the direction of rotation of the coil in the d.c. motor
direction of rotation - reversing direction of current reverses the direction of the magnetic field by reversing the poles of the magnet
how can the force supplied by the motor be increased
-increasing current in the coil
-increasing the strength of the magnetic field
-adding more turns to the coil
how does a loudspeaker work
-alternating current pas through the coil of the loudspeaker, creating a changing magnetic field around the coil
-the current is constantly changing direction, the direction of the magnetic field is constantly changing
-magnetic field produced around the coil interacts with the field from the permanent magnet
-interacting magnetic fields exert a force on the coil
-direction of the force at any instant can be determined using Fleming’s LH rule
-as the magnetic field is constantly changing direction, the force exerted on the coil will constantly change direction, making the coil oscillate
-oscillating coil causes the speaker cone to oscillate, making the air oscillate, creating sound waves
Fleming LH rule
FBI
how is an electromagnet made
wounding a wire around soft magnet such as iron
how to increase strength of a solenoid
-increase number of turns
-increase the current
-wrap solenoid around a soft iron core
magnetic fields of common wire patterns
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what extent of the force will an electron receive if it is travelling perpendicular to magnetic field lines
maximum force
what extent of the force will an electron receive if it is travelling parallel to magnetic field lines
no force
what extent of the force will an electron receive if it is travelling at an angle to magnetic field lines
It will experience a small force
EM induction1
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
opposite of the motor effect1
generator effect/dynamo effect
difference between motor and generator effect1
-in the motor effect, there is already a current in the conductor which experiences a force
-there is no initial current in the conductor but one is induced when it moves through a magnetic field
when does electromagnetic induction happen1
-when the conductor or coil cuts through the magnetic field lines of the magnetic field
-relative movement between the conductor and the magnetic field
-induces a potential difference in the wire
how to measure the size of the induced potential difference of a coil from electromagnetic induction
a sensitive voltmeter
when is current induced from EM induction
when the conductor is part of a complete circuit
factors affecting the induced potential difference
-the speed at which the wire, coil or magnet is moved
-number of turns on the coils of wire
-size of the coils
-strength of the magnetic field
how the speed affect the induced potential difference
-increasing the speed will increase the rate at which the magnetic field lines are cut
-increase the induced potential difference
how does the number of turns of the coil in the wire change the induced potential difference
-increasing the number of turns on the coils in the wire will increase the potential difference induced
-because each coil will cut through the magnetic field lines and the total potential difference induced will be the result of all of the coils cutting the magnetic field liens
how does the size of the coils affect the induced potential difference
-increasing the area of the coils will increase the potential difference induced
-because there will be more wire to cut through the magnetic field lines
how does the strength of the magnetic field affect the size of the induced potential difference
-increasing the strength of the magnetic field will increase the potential difference induced
how does the orientation of the poles of the magnet affect the induced potential difference
reversing the direction in which the wire, coil or magnet is moved changes the direction of the induced potential difference
what does the generator effect generate in a generator
alternating current
what does the generator effect generate in a dynamo
direct current
alternator
type of generator that converts mechanical energy to electrical energy in the form of alternating current
how does an alternator work
-coil turns in a uniform magnetic field
-coil connected to centre-reading meter by metal brushes pressing on two metal slip rings
-coil cuts through the magnetic field lines
-alternating potential difference and current is induced in the coil
how does a dynamo work
-coil rotates
-cuts through field lines
-induces potential difference between the end of the coil
-split ring commutator changes the connections between the coil and brushes every half turn, keeping current leaving the dynamo the same direction
-induced potential difference does not reverse its direction
transformers
a device used to change the value of an alternating potential difference or current
what does a basic transformer consist of
-primary coil
-secondary coil
-iron core(easily magnetised)
how does a transformer work
-alternating current is supplied to primary coil
-current is continually changing direction, producing a changing magnetic field around the primary coil
-iron core is easily magnetised, changing magnetic field passes through it
-changing magnetic field inside the secondary coil
-changing field cuts through the secondary coil, inducing a potential difference
-due to the magnetic field changing the induced p.d. will be alternating, same frequency as ac supplied to the primary coil
-if secondary coil is part of a complete circuit it will cause an alternating current to flow
transformers equations
Vp/Vs = np/ns
p = primary coil
s = secondary coil
V = voltage
n = number of turns
step up up transformer
-increases the p.d. of a power source
step down transformer
decreases the p.d. of a power source
how does the power change across the primary and secondary coil
stay the same
-if step up: current is lower and vice versa
follows P = IV
equation of Ps
Ps = Vp x Ip
