Magnetic Feilds And Induction Flashcards by Kathleen anderson

What are magnetic feilds

Are induce with the movment of charges

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Why are electrons induced by a magnetic feild

Electrons make up the atomic structure are in motion around a nucleus

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What metals are ferromagnetix

Iron
Nickel
Cobalt

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What does ferromagnetism mean

It is when the magnetic dipole can be made to align resulting in the material becoming magnetised

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What is the hand rule for a magnetic field with a straight wire

Left-hand (like doing a thumbs up)
Thumb - electron
Fingers - feild lines

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How can a magnetic field be strengthen

By coiling up the wire

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Whaf is a long coil

Solenoid

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What is the rule for solenoids

Left hand - curl around a water bottle
Finger indicates electrons
The points north of the magnetic field

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What is a solenoid

It is a coil of wire thaf when a current flow through it a uniform magnetic field is produced inside the volume of space of the cylinder

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What is the rule for finding the force on the conductors

Right hand rule
Middle finger- electron
Top finger - magnetic field
Thumb - force

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What happens to a conductor moving in a magnetic feild

It will experience a force which is a result of the magnetic induction

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What is the unit for magnetic induction

Tesla

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For a strong nuclear force what is:
The relative magnitude
Range
Example

1
X10-14
Nucleons in a nucleus

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For electromagnetic force what is:
The relative magnitude
Range
Example

x10-2
Infinity
Contact forces

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For a weak nuclear force
The relative magnitude
Range
Example

x10-5
x10-18
Beta decay in the nucleus

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Foe the gravitational force what is:
The relative magnitude
Range
Example

x10-38
Infinity
Very large masses
Planets

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What is the component velocity for perpendicular

Vsin0

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What Is the component velocity for parallel

Vcos0

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What type of motion will a charged particles with a perpendicular velocity face

It will undergo circular motion

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If the magnetic feild acts into the page then the following applies

Positive- anticlockwise
Negative- clockwise

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What are the applications of magnetic feild

Velocity selector
Mass spectrometer

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What is the arrangement for a velocity selector

If the magnetic and electric field are perpendicular to eachother. A charge with a certain velocity will proceed through the crossed fields undefeated
Only if forces are balanced

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If order to calculate the velocity in the velocity selector what do you do

You equal f=qvB and f=qE
Then make it equal to velocity

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What is a spectrometer used for

It is used to measure the range ot atomic masses of ions of an element.

Whaf happens during the mass spectrometer

They go through the velocity selector They then enter a magnetic field which causes then to follow a circular path

How to calculate the radius in the mass spectrometer

qvB=mv^2/r

Symbol for magnetic induction

Symbol for a battery

One big line one small

Symbol for a capacitor

Two big lines

What is the time constant

Time taken to increase the charge stored by 63% of the difference between initial charge and full charge

What percentage is the time constant

63%

What is the time constant for discharging

37%

What is the discharging time constant definition

Time taken for a capacitor 5o discharge to 37% of it'd initial charge

What are conductors

They contain free electrons that are not strongly boned to any particular atom.

What happens when an emf is applied to a conductor

The electrons dirft along the conductor. This movement of charge is knows as current

What angle are the charged particles at to the magnetic feild

Right angles

If magnetic feild lines are bring crossed what is produced

EMF

Another way can a induced EMF be produced

Stationary conductor

What does the induced voltage depend on

Size of coil, strength of magnetic, rate of change of motion of the magnetic

When the rate of chnage of current is zero

Max current is reached

What is the back emf a result of

A decrease in the rate of change of current which in turn decreases the back emf.

Symbol for inductance

What is the symbol for back emf

Curly E

Unit for rate of change of current

As-1

Units for inductance

Why is the minus sign present on back emf

Because back emf is in the opposite direction to the forward current

How happens to the back emf when the rate of change of current decrease

It will decrease

What does the power supply of the circuit

It was to work against this back emf. This work is stored in the magnetic field around the inductor

Whaf happens to the engery stored when the magnetic field collapses

The engery is immediately released

Whay does the core of a inducer allow for

Storage of energy and controlling of the time it take to get to maximum current

Symbol for an inductor (in q circuit)

The swiggle line

Does the current reach maximum when their is a induction in the circuit

What is the back emf equal to

Equal but opposite to the supply supply

What does a graph of current against time look like

Increase gradient curve from 0

Self - inductance

When a circuit it switched on a sudden change in current produces a changing magnetic feild around the coil that induces emf across the coil

What is lenz's law

States that the induced current (and emf) is always in such direction as to opposed the change that is causing it

Back EMF

Is an induced EMF in a circuit as a result of a changing magnetic feild that opposes the current in the circuit

If you increase the a.c supplies frequencies then what happens to the rate of change of current

It increases

If the rate of change increases then what happens to the back emf and current

The back emf will also increases

If the rate of change increases then what happens to the self induced back emf and current

The back emf will increase and opposed the chnage so the current will decrease

Inductive reactants is a property that...

Arises for inductor in ac circuits as they are frequency dependent components

Symbol for inductive reactance

Inductive reactance is the opposition to

Changing current

If the frequency of the ac supply is high then what happens to the chnage jn current

Large

Ac circuits must deal with what

Resistance qnd reactance

Graph of inductive reactance in a inductor against frequency

Straight line

Inductive reactance in a capacitor against frequency

Sloping down decreasing gradient

What reactance and frequency does capacitors have

Low reactance and high frequencies

Inductor reactance and frequencies

Low reactance Low frequency

What is the diode for

Reverse bias to the power supply. This prevents it from contributing to the circuit during charging

Explain why high frequency signals pass to the component with the capacitor

Capacitor has how reactnace for higher frequencies

Explain why low frequency signals were passed through the inductor

Inductor have low reactance at low frequencies

It was advised to include q diode in the circuit to prevent damage to the laptop when the switch is open. Why is this necessary

Large back emf

Explain how the back EMF is produced

Their is a chnage in current which produces a chnage in magnetic field

By considering the magnetic feild around the inductor, explain why the back EMF produced is large enough to allow the neon lamp to flash

The magnetic feild collapses around the inductor and causes a rapid chnage in current

The inductance of an inductor increases state and happens to the frequency and justify

Frequency decreases Increases inductance increases the time constant

Definition of inductive reactance

Is the opposition to changing current

What is inductance

It isbthe ratio of the induced back emf to the rate of change of current

When the battery I'd switched on what is thr back emf

Equal to the supply voltage

At Imax whaf is the back emf equal to

Capacitive reactance

The opposition a capacitor to changing current