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Physics > Magnetic Fields > Flashcards

Magnetic Fields Flashcards

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1
Q

What is a MAGNETIC FIELD?

A

Region surrounding a magnet or current-carrying conductor where another magnet or current-carrying conductor experiences a force.

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2
Q

What DIRECTION do magnetic field lines go?

A

North to South.

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3
Q

What is the MAGNETIC POLE of a current in a wire going IN?

A

South.

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4
Q

What is the MAGNETIC POLE of a current in a wire going OUT?

A

North.

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5
Q

What is the RIGHT THUMB RULE for a WIRE?

A

Thumb = direction of current
Fingers wrapped around wire = direction of the field.

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6
Q

What is the RIGHT THUMB RULE for a SOLENOID?

A

Thumb = direction of magnetic field.
Fingers wrapped around coil = direction of current.

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7
Q

What affects MAGNETIC FORCE/MOTOR EFFECT?

A
  • Angle of current is to the field
  • Magnitude of magnetic flux density
  • Length of wire
  • Size of current
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8
Q

What is MAGNETIC FLUX DENSITY?

A

The force on a wire per unit current per unit length in a magnetic field. Also known as magnetic field strength.

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9
Q

What is TESLA?

A

Magnetic flux density that causes a 1 Newton Force to act on 1 metre of wire carrying 1 amp of current.

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10
Q

When is MAX FORCE experienced?

A

When current carrying wire is at right angles to the magnetic field lines.

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11
Q

Why does the COIL TURN in a MOTOR?

A
  • Opposite vertical forces on either side of coil (Flemming’s left hand rule) due to magnets on both sides creating a magnetic field.
  • Causes anticlockwise rotation
  • Split ring commutator switches the currents direction, keeping constant anti-clockwise spin.
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12
Q

What is FLEMING’S LEFT HAND RULE for the MOTOR EFFECT?

A

Thumb = force
Index = Field
Middle = current

(CURRENT AND FIELD ARE AT RIGHT ANGLES)

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12
Q

How does a LOUDSPEAKER WORK?

A
  1. alternating current creates changing magnetic field.
  2. current creates electromagnet in core.
  3. Magnetic between electromagnet and permanent magnet exerts force on coil. which is constantly changing.
  4. AC current is same frequency as variation of sound to be emitted.
  5. Coil vibrates at frequency of AC.
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13
Q

How to derive F=BQv?

A

F = BIL
I = Q/t
F=B(Q/t)L
L/t = v
F= BQv

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14
Q

What directions do ELECTRIC FIELDS and MAGNETIC FIELDS act in a deflection tube.

A
  • They act in opposite directions by adjusting the strengths.
  • Use Helmholtz coils.

Ee = Bev.

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15
Q

Why does a charged particle in a magnetic field move in a circle?

A

Magnetic force will always be at right angles to the velocity of the charged particle.

16
Q

What is the radius of the circular motion in a magnetic field?

A

F = BQv
F = mv^2 / r
Solve for r.

17
Q

Why does the time period not depend on velocity in a magnetic field?

A

F = mv^/r
V=Wr
W=v/r
F=mWv
W = 2pi/T
F = bqv

Equate these two together.

18
Q

Why do particle velocity paths become more spiral in a magnetic field?

A

Particles lose kinetic energy through ionising collisions in air. This makes the path more curved and thicker.

19
Q

What is MAGNETIC FLUX?

A

The quantity of B lines passing through an area of Am^2

20
Q

What is FLUX LINKAGE?

A

The total amount of flux through a loop of wire.

21
Q

What is FARADAY’S LAW?

A

The magnitude of EMF induced in a conductor equals the rate of change of flux linkage of which the conductor cuts through the magnetic flux.

22
Q

What two ways can EMF be induced?

A
  1. Moving a current-carrying through a B wire.
  2. Move a magnet through a coil of current-caryign wire.
23
Q

Why is EMF proportional to velocity?

A

E = change in Φ / change in t
Φ = BA
E = Change in BA / change in t
A = Length x velocity x time
E = B x change in Lvt / change in t
E = BLv
E is proportional to v

24
Q

What is FLEMING’S RIGHT HAND RULE for GENERATING ELECTRICITY?

A

Thumb = direction of force
Index finger = magnetic field
Middle finger = INDUCED current

25
Q

What is the MAINS POWER SUPPLY in VOLTAGE?

A

230V

26
Q

What is LENZ’s LAW?

A

Direction of EMF induced in a conductor is such that it opposes the charge producing it.

27
Q

How does a VINYL PLAYER work?

A
  • Stylus passes through grooves, causes magnet it is attached to to vibrate
  • Electromagnet is created as current passes through the coil around the iron core.
  • Two magnetic fields overlap.
  • Vibrations cause magnetic flux to be cut, producing an EMF, opposing current in coil.
28
Q

Explain what is happening when a magnet is dropped through a coil.

A
  • E = N * Change in Φ / change in t
  • N is constant so the area underneath the graphs are always equal.
  • Increase in EMF when magnet gets closer to the coil.
  • Negative gradient when magnet passes though the coil because of changing magnetic flux.
  • Larger negative amplitude because E is proportional to v. Magnet is accelerated due to gravity.
29
Q

Why does current decrease when a motor begins to spin fast?

A

E is proprtional to v, EMF opposes current so if EMF increases, current will decrease.

30
Q

What are the properties of Transformers?

A

Soft - loses magnetism very quickly after being shut off.
Laminated - reduces heat transfer.
Iron core - produces magnetic field that wraps around.

Physics (18 decks)

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