magnetism

Question 1

what is a magnet

Answer 1

1. made of tiny atomic magnets (i.e. unpaired electrons which spin on their axes while moving around nucleus of atom) and interact with one another –> these electrons are known as domains
2. in a magnet, domains are aligned in an orderly manner, in the same direction –> net magnetisation
   a) each arrow is arranged directly behind the arrow in front of it, so N poles are cancelled out by adjacent S poles
   b) at the ends, atomic magnets are ‘free’ –> N & S poles
3. not a magnet: domains are arranged disorderly, point in random directions, magnetic field of domains cancel one another out, net magnetic effect = 0

Question 2

properties of magnets

Answer 2

1. like poles repel, unlike poles attract
2. rest in north-south direction
3. have two poles
4. attract magnetic materials

Question 3

when does induced magnetism take place

Answer 3

1. when a magnetic material is placed close to a strong magnet or within a current-carrying solenoid –> temporary magnets
2. can happen without (placing a magnet adjacently next to a magnetic material) or with contact (paper clips attracted to a magnet becomes an induced magnet to attract other paper clips

Question 4

ways of making magnets

Answer 4

1. stroking
2. electrical current using direct current

Question 5

what is stroking

Answer 5

1. an unmagnetised steel bar is stroked several times from one end to another, with one of the poles of a permanent magnet, which is being used throughout
2. the stroking magnet should be lifted sufficiently above the steel bar between successive strokes
3. the pole produced at the end of the steel bar where the strokes finish is opposite to the stroking pole used
   - only stroke STEEL –> stronger magnetic field strength

Question 6

what is the electrical method using direct current

Answer 6

1. when a large direct current flows through solenoid, a strong magnetic field is produced
2. magnetic field aligns the magnetic domains in the steel bar –> aligns domains –> magnetised

Question 7

ways to determine direction of magnetic field

Answer 7

1. right hand grip rule
2. observing direction of current flow at the end of the solenoid

Question 8

right hand grip rule

Answer 8

1. grip solenoid using right hand
2. curl fingers in the direction of the current flow in the solenoid
3. extended thumb will point in the direction of north pole

Question 9

how to observe direction of current flow

Answer 9

1. clockwise direction: south pole
2. anti-clockwise direction: north polemic

Question 10

ways to demagnetise magnets

Answer 10

(1. heating)
2. hammering
3. electrical method using alternating current

Question 11

what is hammering

Answer 11

magnet is placed in east-west direction –> minimises influence of earth’s magnetic field during demagnetisation before hitting

Question 12

what is electrical method using alternating current

Answer 12

1. place a magnet inside a solenoid in an east-west direction
2. connect solenoid to an alternating current supply –> disrupts orderly alignment of domains –> becomes randomly arranged
3. slowly withdraw magnet with a.c still flowing in the solenoid, until it is some distance away or gradually reduce current to zero

Question 13

storage of magnets

Answer 13

magnets are stored in iron keepers, with unlike poles next to each other –> magnetic field is retained, preserve strength

Question 14

properties of soft/magnetic materials