Section 11 - Magnetic Fields Flashcards

1
Q

When a magnetic field is perpendicular to a current-carrying wire, does the wire feel a force?

A

Yes, the magnitude of the force is BIL

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2
Q

Flemming’s left hand rule for motors represents what properties on what fingers?

A

Thumb - Thrust/Force
First dinger - Field (Magnetic)
SeCond finger - Current

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3
Q

What is magnetic flux density (B)?

A

Flux density measured in Tesla (T0 or Webers/metres^2, is the flux per metre^2

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4
Q

A charged particle moving through a field feels a force when it is travelling along the field lines or perpendicular to them?

A

Perpendicular to the field

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5
Q

Is the force applied to the particles applied perpendicular to the particles motion or in one direction?

A

Perpendicular to its motion, causing it to move in circular motion

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6
Q

Which fields do cyclotrons use?

A

An electric field and a magnetic field

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7
Q

How does a Cyclotron work and what’s the electric and magnetic field’s purpose in a cyclotron?

A
  1. A cyclotron is made up of 2 semicircular elecrodes called “Dees” with a magnetic field applied perpendicular to the Dees and an alternating pd applied between the Dees
  2. Each Dee is a metal electrode with opposite charges, this creates an electric field in the gap between the 2 Dees - this is what accelerates the particles
  3. The magnetic field causes the particles to move in a circular motion, which allows it to gain speed whilst minimising space - as they speed up the radius of their motion increases, until it breaks free tangential to one of the Dees
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8
Q

What is flux linkage?

A

NΦ = The number of turns cutting the flux one time

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9
Q

What is Faraday’s Law?

A

The induced e.m.f. is directly proportional to the rate of change of magnetic flux linkage

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10
Q

What is Lenz’s law?

A

The direction of the induced e.m.f. is such as to oppose the change that induces it

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11
Q

What happens when you move a straight conductor through a magnetic field?

A
  • The electrons experience a force pushing them to one end of the conductor creating an emf across the conductor
  • The rod obeys Faraday’s law, it is changing flux as it moves through the field hence and e.m.f. is induced
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12
Q

Describe how one would use an oscilloscope

A
  • Oscilloscopes are used to displace AC waves, the x axis is called the time base and shows how long it takes the wave to move 1 division and the y axis shows how much PD is needed to move the way up 1 division
  • Using this we find the peak voltage, time period and frequency
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13
Q

How does a transformer work?

A
  • A primary coil wrapped around an iron core with an alternating p.d. creates an alternating magentic field, this magnetic field induces an e.m.f. in a secondary coil also wrapped around the core
  • This creates a current in the secondary coil
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14
Q

What kind of current is produced by a transformer and why?

A
  • An alternating current
  • An e.m.f. is induced by a changing magnetic field, hence the e.m.f. induced is alternating producing an alternating current
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15
Q

Why are transformers used?

A
  • By changing the number of coils, the transformers can be used to increase the voltage and reduce current when transporting power, with minimal energy loses
  • The voltage is then dropped again locally to ensure safe usage in households
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16
Q

In a step-up transformer, does the secondary coil or primary coil have more coils?

A
  • The secondary coil
  • Step-up transformers increase the voltage, hence more coils need to be in the secondary coil for a larger p.d.
17
Q

What is an eddy current?

A
  • As the primary coil’s magnetic field induces e.m.f. in the secondary coil, it also induces e.m.f. and hence mini currents within the iron core
  • These are known as eddy currents
18
Q

Why are eddy currents a problem?

A
  • By Lenz’s law the e.m.f. created and its field opposes that of the primary coil
  • This causes energy los via resistive heating of the iron core by the eddy currents, which reduces efficiency
19
Q

How can you reduce eddy current losses?

A
  • Use a laminated core
  • Thin sheets of iron with an electrical insulator in between, which reduces the eddy currents circuit