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Physics > Magnetism > Flashcards

Magnetism Flashcards

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1
Q

What do magnets produce?

A
  • all magnets produce a magnetic field (a region where other magnetic maturely experience a force)
  • the field lines go from north to south
  • the magnetic fields are strongest at the poles of a magnetic so the magnetic force is too
  • Close field lines are together the stronger the force
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2
Q

What magnets attract each other?

A

Unlike magnetic pole attract and like magnetic poles repel

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3
Q

How do you create a uniform field?

A
  • Placing the north and south poles of two bar magnets near each other creates a uniform field between two poles
  • placing two north’s or souths towards each other leads to repulsion
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4
Q

How can plotting compasses be used to show magnetic fields?

A
  • inside a compass there is a needle (small bag magnet)which always lime up with the magnetic field it’s in
  • put the magnet on paper and draw around it
  • place the compass on the paper near the magnet and the needle will point in the direction of the field line at this position
  • mark the direction of the needle by drawing two dots either end
  • switch the direction of the compass needle and put a dot, repeat and join up the marks made
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5
Q

What do plotting compasses point when not near a magnet and what is this proof of?

A

They will always point towards the earths’s North Pole as the earth generates its own magnificent field (North Pole is magnetic South Pole)
-this shows the inside of the earth (core) must be magnetic

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6
Q

What is the difference between permanent and induced magnets?

A

Permanent magnets product their own magnetic field all the time

  • induced magnets only produce a magnetic field while they’re in another magnetic field
  • therefore by putting any magnetic material in a magnetic field it becomes an induced magnet
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7
Q

What happens when you take away the magnetic field of an induced magnet?

A
  • they return to normal and stop producing a magnetic field, how quickly depend on their material
  • magnetically soft materials e.g. pure Iron and nickel loose magnetism very quickly
  • magnetically hard materials like steel lose magnetism slowly (permanganate magnets are made from this)
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8
Q

What are some uses of magnets?

A
  • Fridge doors to keep them permanently closed
  • cranes use induced electromagnets to attract and move magnetic materials
  • maglev trains use magnetic repulsion to make trains float slightly above the track reducing friction losses and to propel them along
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9
Q

What happens when a current flows through a long straight conductor?

A

A magnetic field is created around it

  • the field is mad duo of concentric circles to the perpendicular wire through the centre
  • the larger the current or the closer you at the the wire the stronger the field is
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10
Q

What is the right hand thumb rule?

A

When your right thumb points in The direction of conventional current the direction your fingers turn shows the direction of the magnetic field
-changing the direction of current changes the direction of the magnetic field

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11
Q

What happens when a current carrying wire is out between two magnetic fields?

A

The two magnetic fields interact and results in a force on the wire
-the wires also exert and equal and opposite force on the magnet

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12
Q

What is Flemings left hand rule?

A
  • used to find direction of the force on a current carrying wire
  • your thumb, first finger and second finger must all be 90° perpendicular to each other
  • first finger is field, second is current and thumb is motion/Force
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13
Q

How can you find the size of the force?

A

F= BIL

  • B is the magnetic flux density showing the strength of the magnetic field
  • L is length of the conductor and I is the size of the current
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14
Q

How could the force on the wire be increased or reversed?

A
  • stronger magnet, greater current, more voltage

- to reverse the force on the wire change the direction of the current or swap the poles around

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15
Q

What is a solenoid?

A
  • a loop of current carrying wire (this increases the strength)
  • inside the centre you get lots of field lines pointing in the same direction, forming a very long almost uniform field, so they reinforce so is stronger
  • outside the overlapping field lines cancel out so it is weaker
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16
Q

How do you increases the strength of a solenoid?

A
  • placing a block of iron in the centre of the coil which become an induced magnet
  • more turns of the coil
17
Q

What is electromagnetic induction?

A

Then induction of a potential different which induces a surreal in a wire which is experiencing a change in magnetic field

18
Q

How do you get electromagnetic induction?

A
  • moving/rotating a magnet in a coil of wire or a conductor in a magnetic field (small local scale in lab)
  • if you move or rotate the magnet in the opposite direction then the current will be reversed or if the polarities switch
  • if you continually move the magnet /coil backwards and forwards in the same direction it produces an alternating current
19
Q

What do we mean when the current opposes the change made to it?

A
  • when a current is induced in a wire that current produces its own magnetic field
  • the algebraic fie,d created by an induced current always acts against the change
  • this creates a changing magnetic field
20
Q

How do power stations do a large scale generation of electrical energy?

A
  • burn fossil fuels to heat water into steam which turns a turbine
  • the turbine is connected to a powerful magnet inside a generator
  • as the turbine spins the magnet spins inducing a large PD and a.c. In the coils
  • the coils are joined in parallel to produce a single output
21
Q

How do we used the force on a conductor in a magnetic field to produce rotational movement?

A
  • forces act on the two side arms of the current carrying coil of wire
  • these forces act in opposite direction (FLHR) so the coil rotates
22
Q

What is a dynamo?

A
  • we rotate a coil of wire sitting in a mag.field.
  • this produces a current which changes every half term with EM induction
  • therefore we use a split ring commutator to switch the polarities every half term so the current travels in one direction (d.c.)
23
Q

What is an alternator?

A
  • work in the same way as a dynamo by generate a.c.

- so instead of a split ring they use slip rings and brushes so the contacts don’t swap so generate a.c.

24
Q

What are microphones?

A
  • sound waves but a diaphragm meaning it moves. This moves a coil of wire sitting in a magnetic field
  • Louder sound waves move the diaphragm further
  • this induces a current in the wire
25
Q

How do loudspeakers work?

A
  • input a.c. Current in which moves a coil of wire in a magnetic field
  • force is generated on the cone making it vibrate exciting it in either direction
  • paper come moves air producing a pressure difference and hence causes a sound wave
26
Q

What are transformers?

A

-use induction to change the size of the potential difference of one alternating current
They have two coils of wire (primary and secondary) joined with an iron cord
-when an a.c. P.d is applied across the primary it produces an alternating magnetic field meaning the magnetism in the iron core also alternates
-this changing magnetic field induces a p.d in the secondary coil

27
Q

What is good about transformers about their waste and the equation ?

A

They are almost 100% efficient so you can assume their input power is equal to the output power
Vp x Ip = Vs x Is

28
Q

What are step up transformers and step down transformers?

A

Step up step the p.d up, they have more turns in the secondary coil than in the primary
Step down step the p.d down, they have more turns on the primary than the secondary

29
Q

Why does the national grid use step up transformers?

A
  • the national grid has to transfer loads of energy each second so has high power (P=IV)
  • but a high current makes wires heat up due to collisions so loss of energy is wasted to thermal energy stores
  • therefore by using low resistance wires and a high voltage you reduce energy lost so greater power
30
Q

Why does the national grid use step-down transformers?

A
  • when transporting energy voltage is really high and current low
  • Hugh voltage can damage appliances and isn’t useable, step-down transformers being the p.d. back down to a safe and useful level when it reaches the consumer (230V)
31
Q

What is the equation that shoes the ratio between potential difference in the primary and secondary coils?

A

Vp/Vs = Np/Ns

32
Q

What is an electromagnet?

A

A magnet than be controlled (turned on or off)by an electric current

33
Q

Why do you use a split ring commutator?

A
  • without this the forces on the top and bottom wires would counteract so would never fully rotate
  • swaps the contacts every half turn to keep the motor rotating
34
Q

How does the split ring commutator overcome the gap as the polarities switch?

A

Momentum of the rotation keeps it moving

Physics (14 decks)

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