magnetic fields

Question 1

what is a magnetic compass?

Answer 1

a needle pivoted at its centre

Question 2

explain how to investigating bar magnets?

Answer 2

suspend a magnet and mark the end that points north as N. then hold a second magnets N against the suspended magnet. it should repel and switch sides.

Question 3

what is the general rule with bar magnets?

Answer 3

like poles repel, unlike poles attract.

Question 4

any iron or steel object can be?

Answer 4

magnetised

Question 5

explain how to find the magnetic field around a bar magnet

Answer 5

place the magnet under a sheet of paper and sprinkle iron filings on top. they will form a pattern of lines. they will be more concentrated at the poles, because it is stronger here.

Question 6

explain what a plotting compass will do?

Answer 6

when placed in the magnetic field, it will point away from the north pole and towards the south.

Question 7

the direction of a line of force is

Answer 7

always from north to south

Question 8

an unmagnetised magnetic material can be magnetised by?

Answer 8

placing it in a magnetic field

Question 9

what material is most likely to be used for permanent magnets?

Answer 9

steel

Question 10

what is a solenoid?

Answer 10

a long coil of insulated wire.

Question 11

the magnetic field in a solenoid is produced in and around when?

Answer 11

current is passed through a wire

Question 12

the magnetic field in a solenoid can be increase in strength by?

Answer 12

increasing the current

Question 13

the magnetic field in a solenoid can reverse its direction by?

Answer 13

reversing the current

Question 14

to increase the force in a electromagnet you can?

Answer 14

increase number of coils
add an iron core
increase the current
move magnetic material closer

Question 15

the magnetic field inside a solenoid is?

Answer 15

strong and uniform

Question 16

what is an electromagnet?

Answer 16

a solenoid in which the insulated wire is wrapped around an iron core

Question 17

list some uses of electromagnets

Answer 17

electric bell, circuit breaker, scrapyard crane

Question 18

how does an electromagnetic work in some of the things it does?

Answer 18

it attracts an iron armature, each opens a switch

Question 19

explain a practical to test the strength of an electromagnet

Answer 19

use an electromagnet to hold a flat iron bar. suspend the bar and measure the smallest amount of current needed to hold it. then increase weight and repeat readings. repeat and after increasing amount of turns. plot results that draw conclusions about what factors affect strength.
safety: make sure it does not get too hot.

Question 20

the size of a force can be increased by?

Answer 20

increasing current

using a stronger magnet

Question 21

explain flemmings left hand rule

Answer 21

thumb: movement
1st finger: current
2nd finger: field
you can work out the direction of force from this.

Question 22

what is the equation for magnetic flux density?

Answer 22

force (N) = magnetic flux density (T) x current (A) x length (M)

Question 23

what is magnetic flux density a measure of?

Answer 23

the strength of a magnetic field

Question 24

what is the unit for magnetic flux density

Answer 24

tesla