magnetism and electromagnetism

Question 1

what is a magnet

Answer 1

any material or object that produces a magnetic feild such as a bar magnet

Question 2

what directions do feild lines move from

Answer 2

north to south

Question 3

what happens to the strength of the feild when the feild lines are closer together

Answer 3

the feild is stronger

Question 4

how can you find out the poles and field lines of a permanent magnet

Answer 4

use a compass, the arrow in the compass is a bar magnet and therefore will line up with feild lines and will always point toward the south pole of the magnet

Question 5

what is a magnetic element/material

Answer 5

any object that can be influenced by a magnetic feild and has the potential to become a magnet

Question 6

give 4 examples of a magnetic element/ material

Answer 6

nickel, cobalt, iron, steel

Question 7

what is the difference between a permanent magnet and an induced magnet

Answer 7

a permanent magnet produces its own magnetic feild yet an induced magnet only have a temporary magnetic feild

Question 8

how are induced magnets made

Answer 8

when a piece of magnetic material is placed into a feild of a permanent magnet

Question 9

what will always happen between a induced magnet and a permanent magnet

Answer 9

they will always attract

Question 10

what does it mean when a material is magnetically soft - give example

Answer 10

a material will loose their magnetism really quickly such as nickel or iron

Question 11

what does it mean when a material is magnetically hard - give example

Answer 11

a material keeps their magnetism for a longer period of time such as steel

Question 12

what is an electromagnet

Answer 12

an electric current that produces their own magnetic feild

Question 13

what is the right hand rule (how do you use it)

Answer 13

put your right hand into a fist and point thumb in the direction of the current flow, the direction that your fingers curl = the direction of the magnetic feild

Question 14

what is a solenoid

Answer 14

a coil of wire which has a magnetic feild like a bar magnet with electric current going out the north pole

Question 15

how are solenoids made

Answer 15

take two wires which have a current flowing through which therefore have a magnetic feild in each wire. these magnetic fields combine when wires are joined to make a solenoid

Question 16

describe the properties of the magnetic of a solenoid

Answer 16

strong and uniform

Question 17

why are electromagnets useful

Answer 17

they are only a magnet when current flows through the wire

Question 18

how can you reverse the direction of the magnetic feild in an electromagnet

Answer 18

reverse the direction of the current flow which reverses the direction of the current flowing therefore poles and magnetic fields flip

Question 19

give four ways to increase the electromagnetic stength

Answer 19

1 - increase the current
2 - increase the turns in coil
3 - decrease the length of the coil
4 - add an iron core as it will become a soft magnet increasing the magnetic feild strength

Question 19

what is the motor effect

Answer 19

a current carrying a wire in the presence of a magnetic feild will experience a force

Question 20

what happens if a wire carrying a current (and therefore a magnetic feild) is placed between two bar magnets

Answer 20

the magnetic feild from the bar magnets and the wire will interact resulting in a force on the wire

Question 21

what position does the wire need to be in, in order to feel the full force

Answer 21

needs to be at 90 degrees to the magnetic feild of the bar magnet

Question 22

what would happen if the wire was in the same direction as the magnetic feild

Answer 22

there would be no force

Question 23

how can we find the direction of a force
(explain Fleming’s left hand rule)

Answer 23

first finger = the magnetic feild (north to south)
second finger = the current
thumb = direction of the force

Question 24

what would happen if another wire (with a current flowing in an opposite direction) was placed between the bar magnets

Answer 24

it will experience a force in the opposite direction, if the two wires were connected the current would go in the positive terminal (on the right) and out the negative terminal (left) and they would feel opposing forces, the coil will spin anticlockwise.

Question 25

what happens when the motor rotates 180 degrees and how can we stop this happening

Answer 25

the current travels in the opposite direction and the force has also swapped, the coil will then turn anticlockwise - fix by changing the direction of the current every half turn

Question 26

when using a motor, how can we change the direction of the current every half turn

Answer 26

using a split ring commutator

Question 27

how does a split ring commutator work

Answer 27

it swaps the positive and negative connections every half turn so the direction of the current also swaps every half turn meaning forces on the coil will always act in the same direction and therefore coils will always rotate in the same direction

Question 28

hoe can you increase the speed of an electric motor

Answer 28

1 - increase the current
2 - add more turns
3 - increase the magnetic feild strength by using stronger magnets