Magnetic Fields

Question 1

What are the 3 rules when drawing magnetic patterns?

Answer 1

• like poles repel
• unlike poles attract
• field lines from north to south

Question 2

How are magnetic fields produces in electric circuits?

Answer 2

moving charged particles within a wire

Question 3

When are magnetic field lines concentric?

Answer 3

long straight current carrying conductors

Question 4

What do magnetic field lines of a solenoid resemble?

Answer 4

magnetic field lines of a bar magnet

Question 5

What are the magnetic field lines of a solenoid?

Answer 5

uniform field with a solenoid core

Question 6

What is magnetic flux density?

Answer 6

strength of the magnetic field

Question 7

How is Newton’s third law applied to current carrying conductors?

Answer 7

wire and magnet experience equal and opposite forces

Question 8

Within Flemming’s left hand rule which fingers represent which component?

Answer 8

• thumb: motion (up/down)
• index: field (N to S)
• middle: current (direction)

Question 9

What is the SI unit of magnetic flux density?

Answer 9

tesla (T)

Question 10

When does does magnetic flux density equal 1?

Answer 10

when a wire carrying a current of 1A placed perpendicular to the magnetic field experiences a force of 1N per metre of its length

Question 11

Why do charged particles in magnetic fields move in a circular path?

Answer 11

because magnetic force is perpendicular to velocity

Question 12

Why is no work done when the particle moves in a circular path?

Answer 12

force has no component in direction travel so velocity remains constant

Question 13

What is the centripetal force when a particle moves in a circular path?

Answer 13

BQV

Question 14

What is a velocity selector?

Answer 14

device used in instruments such as mass spectrometer to select charged particles of a specific speed

Question 15

Define magnetic flux:

Answer 15

product of the component of magnetic flux density perpendicular to the area

Question 16

Define magnetic flux linkage:

Answer 16

product of the number of turns in coil N and magnetic flux

Question 17

What units do magnetic flux and magnetic flux linkage use?

Answer 17

Weber (W)

Question 18

What is Faraday’s law?

Answer 18

the magnitude of the induced emf is directly proportional to the rate of change of magnetic flux linkage

Question 19

What is Lenz’s law?

Answer 19

the direction of the induces emf or current is always such to oppose the charge producing it

Question 20

How does an AC generator work?

Answer 20

a coil is rotated at a steady speed in a magnetic field

Question 21

How does magnetic flux linking the coil in an AC generator vary?

Answer 21

sinusoidally

Question 22

What is the negative gradient of a flux linkage against time graph equal to?

Answer 22

EMF

Question 23

What is supplied to the primary input coil of a transfprmer?

Answer 23

alternating current

Question 24

What does passing alternating current through a transformer cause?

Answer 24

varying magnetic flux in the soft iron core

Question 25

What does the iron core of a transformer ensure?

Answer 25

no magnetic flux is lost between the primary and secondary coil

Question 26

In accordance to Faraday’s law what is produced across the ends of a secondary coil in a transformer?

Answer 26

varying emf

Question 27

What are transformers used for?

Answer 27

to step up and step down voltages

Question 28

What is equal in a 100% efficient transformer?

Answer 28

output power and input power