Magnetic Fields

Question 1

similar to how electric fields exert forces on charges, what do magnetic fields affect

Answer 1

poles

Question 2

what is the definition of a magnetic field

Answer 2

a region of space that will cause a magnetic pole to feel a force

Question 3

what do the field lines of a magnetic field show

Answer 3

the direction that a lone north pole will be pushed / attracted towards

Question 4

using that knowledge, what direction are the magnetic field lines of a magnet with a north and south pole pointing towards

Answer 4

• from the north pole to the south pole

- because the north pole would be attracted to the south pole

Question 5

how are the directions of the field lines of magnetic fields similar to electric fields

Answer 5

• similar to how the +ve charge has its field lines pointing outwards and a -ve charge has its own inwards
• the north pole has its lines pointing outwards and thes south pole has its lines pointing inwards

Question 6

what is the other name for magnetic field lines

Answer 6

lines of magnetic flux

Question 7

what do closer magnetic fields lines indicate

Answer 7

a stronger magnetic field

Question 8

what is magnetic flux density

Answer 8

• the strength of a magnetic field

- measured by the ratio of magnetic flux to the area it is passing through (literally just density)

Question 9

what is the symbol and unit for magnetic flux density

Answer 9

• symbol = B

- unit = Tesla (T)

Question 10

what do the field lines of a typical magnet with a north and south pole look like

Answer 10

• curved lines travelling and pointing from the north to the south pole
• these lines connect with the outer side of the bases
• the inner base (face) of the north pole has closer lines that point outwards (still curving out)
• while the inner base of the south pole has closer lines that point inwards (still curving out)

Question 11

what is the important rule you need to remember when drawing magnetic field lines of magnets, other than the directions

Answer 11

• that all the lines originate and connect from the faces of the north and south pole
• basically no lines are touching / connected to the long side of the rectangle

Question 12

if you were to try and pick up a paperclip with a magnet, where would the clip ‘prefer’ to be picked up of, geometrically speaking in terms of the magnet, and why

Answer 12

• the clip would prefer to be attracted to one the end of the magnet (the north / south pole faces)
• because the magnetic field is stronger at those ends
• signified by the closer lines of magnetic flux on the faces
• so it would be attracted to those ends the most compared to any other side

Question 13

what is the symbol and unit for flux

Answer 13

• the symbol is a capital sigma (not the summation sigma, the “Io” sigma)
• the units are weber (Wb)1

Question 14

what does the measurement of flux indicate (remember definition of magnetic flux)

Answer 14

the strength of the effect of a given field

Question 15

what is the equation for flux

Answer 15

Bsin0 * A

Question 16

what are the variables in the equation for flux

Answer 16

• B = flux density

- A = area

Question 17

why is the sin theta there

Answer 17

because you should only be taking the component of the flux density that is perpendicular to the area

Question 18

what would the equation be if the magnetic flux was in one uniform direction and at 90 degrees to the area

Answer 18

• it would simply be perpendicular to the area
• in other words, sin90 = 1
• so the equation simplifies to flux = BA

Question 19

what is the more general name for magnetic flux density

Answer 19

magnetic field strength

Question 20

interactions between magnetic fields and charged particles / conductors allow motors to operate. practically speaking, between a single strand of wire and a coil of wire which is used

Answer 20

a coil of wire

Question 21

why is it ineffective to use a single strand of wire

Answer 21

• when magnetic flux is made to interact with the wire,

- the effect on a single strand is too small

Question 22

what is the effect of using a coil of wire rather than a strand

Answer 22

• if the wire is coiled up, the field can interact with each turn on the coil
• meaning if you have n number of coils
• the effect that would be on one strand would be multiplied n times

Question 23

what is the definition of flux linkage

Answer 23

the amount of magnetic flux interacting with a coil of wire

Question 24

what are the two equations for flux linkage

Answer 24

• flux linkage = N * flux
• as flux = BA
• flux linkage = BAN