chapter 23 Flashcards

1
Q

What is a magnetic field?

A

A field surrounding a permanent magnet or current carrying conductor in which magnetic objects experience a force.

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2
Q

How do magnetic fields lines map to magnetic fields

A
  • Arrows point from north to south pole.
  • The closer the arrows are the stronger the magnetic field is.
  • uniform magnetic fields have lines equally spaced.
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3
Q

How do magnetic fields form in permanent magnets and current-carrying conductors?

A
  • In a permanent magnet, the electrons in the atoms making up the atom align and spin around the nuclei in an ordered manner to produce an overall magnetic field.
  • In a current-carrying conductor, the field is created by the electrons moving through the wire.
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4
Q

Magnetic field line pattern in flat coil, current-carrying wire and solenoid.

A
  • Follow direction of flat circle, straight line, and long coil with right hand rule.
  • For solenoid the four fingers represent the current and the one finger represents the magnetic field.
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5
Q

Magnetic force formula.

A

F = BILSinX.
Where X is the angle between the current and magnetic field lines.

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6
Q

What is magnetic flux density? (With unit symbol and SI unit).

A

B is the symbol for magnetic flux density
Unit: Teslas, T
SI Unit: 1 N A-1M-1

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7
Q

Derive the formula for the force on an electron in a magnetic field.

A

F =BIL
Length of a region wire can be written as Vt
The current of a shaded region can be written as NQ/t
These substitutions combine to give F = BNQV
For a single electron this becomes F = BeV

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8
Q

A practical for determining magnetic flux density

A

Two magnets are put side to side on a scale and it is zeroed.
A current-carrying wire is fixed and perpendicular to the magnetic field.
A current is ran through the wire and is varied, the force on the wire = equal to the force of the magnet downwards and hence the reading on the scale.
Vary current and force, then plot force against current and the gradient = BL

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9
Q

Relation of the Magnetic force to centripetal force

A

The centripetal force is provided by the magnetic force.
So for the electron, BeV = mv2 / r

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10
Q

How does a velocity selector function?

A

Two magnets are put side to side to create a magnetic field, and two charged plates are put to create a perpendicular electric field
The electric field force is F = EQ
The magnetic field force is F = BQV
So when the forces balance, E/B = V and this is the particular velocity which will travel straight

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11
Q

Magnetic flux, with units

A

The product of the component of the magnetic flux density perpendicular to the area and the cross sectional area
Φ = BCosXA
X is the angle between the normal to the surface area and the magnetic flux density
The weber, Wb = 1 T m2

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12
Q

Magnetic flux linkage

A

The product of the number of turns and magnetic flux, Magnetic flux = NΦ

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13
Q

Faradays law

A

The emf induced is proportional to the change in magnetic flux over change in time

It is equal to the negative change in magnetic flux over change in time

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14
Q

Lenz’s law

A

The direction of the induced e.m.f. or currrent is always opposite to the change producing it

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15
Q

Formulas for transformers

A

Ns/Np = Ip/Is = Vp/Vs

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