Magnetic Fields

Question 1

Magnetic field

Answer 1

A place that will cause a magnetic pole to experience a force

Question 2

Magnetic flux definition

Answer 2

is a quantity which signifies how much of
a magnetic field passes perpendicularly through some area

Question 3

The magnetic flux is maximum when…

Answer 3

the magnetic field lines are perpendicular to the coil area

Question 4

The magnetic flux is minimum when…

Answer 4

the magnetic field lines are parallel to the coil area

Question 5

Magnetic flux linkage definition

Answer 5

The product of the magnetic flux and the number of
turns of the coil (Wb turns)

Question 6

The motor effect:

Answer 6

• When a current flows in a wire a magnetic field is produced around the wire
• Increasing the current will increase the strength of the magnetic field produced
• Therefore, if a current carrying wire is placed in a magnetic field it will experience a force

Question 7

Flemings left hand rule

Answer 7

• Thumb = motion
• First finger = magnetic field
• Second finger = current

Question 8

Electro magnetic induction

Answer 8

The process in which an e.m.f is induced in a closed
circuit due to changes in magnetic flux (linkage)

Question 9

Explain how shaking the torch produces an
electric current

Answer 9

• Lines of magnetic flux cut through coil of wire
• Reference to electromagnetic induction
• Therefore is a complete circuit so there is current in the coil

Question 10

Factors that will increase the induced e.m.f are:

Answer 10

• The speed of the magnet through the coil
• Adding more turns to the coil
• Increasing the strength of the magnet

Question 11

Alternating voltage

Answer 11

When a coil rotates in a uniform magnetic field, the magnetic flux through the coil will vary as it rotates, this will induce an e.m.f that also varies

Question 12

A coil in a magnetic field can act as a generator. The coil rotates. Explain how this produces a current in the coil.

Answer 12

• The coil cuts magnetic field lines
• Inducing an emf
• Generating current because there is a closed circuit

Question 13

Increasing the coil’s frequency of rotation increases:

Answer 13

• The frequency of the alternating voltage
• The amplitude of the alternating voltage

Question 14

A transformer is made up of:

Answer 14

• A primary coil
• A secondary coil
• An iron core

The primary and secondary coils are wound around the soft iron core. The soft iron core is necessary because it creates flux linkage between the primary and secondary coils

Question 15

Types of transformers:

Answer 15

• step up transformer (increase voltage)
• step down transformer (decrease voltage)

Question 16

What is conserved across transformers?

Answer 16

Power and therefore energy

Question 17

Explain how a lower pd is produced across the
secondary coil in a step down transformer

Answer 17

• Alternating current produced alternating magnetic
  flux
• Magnetic flux is linked to secondary coil by iron core
• Changing magnetic flux INDUCES emf in secondary
  coil
• Less turns on secondary coil

Question 18

Faraday’s law

Answer 18

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

Question 19

Lenz’s law definition

Answer 19

The induced e.m.f is set up in a direction to produce
effects that oppose the change causing it

Question 20

Lenz’s Law dictates:

Answer 20

-The direction of the e.m.f, and hence the
current, must be set up to oppose the
incoming magnet
-Since a north pole approaches the coil face,
the e.m.f must be set up to create an induced
north pole
-This is because two north poles will repel each
other

Question 21

Explain how a loudspeaker works:

Answer 21

• An alternating potential difference is applied to coil
• This produces an alternating current in the coil
• Current in coil causes a magnetic field
• Field changes direction with same frequency as AC
• Coil´s field interacts with permanent magnet´s field
• Therefore coil experiences an alternating force
• This causes the cone to vibrate