Magnets

Question 1

what is a magnetic field ?

Answer 1

region where magnetic materials experience a force

Question 2

what is the uniform field ?

Answer 2

magnetic field of north and south bar magnets close together

Question 3

How do you test for magnetic field patterns ?

Answer 3

can use multiple compasses to see magnetic field

can use iron fillings to see magnetic field (put magnet under paper with iron on top)

Question 4

What is inducing magnetism ?

Answer 4

when a magnet goes near a magnetic material, the material acts a magnet, closer magnet is to material, the stronger induced magnetism

Question 5

what happens to a current carrying wire ?

Answer 5

current carrying wire creates a magnetic field around
larger the current, stronger the magnetic field
direction of magnetic field depends on direction of current

Question 6

what is a solenoid?

Answer 6

coil of wire with a strong and uniform magnetic field

Question 7

What is an electromagnet?

Answer 7

current-carrying solenoid creates a strong and uniform magnetic field
field is just like a bar magnet field
ends of solenoid act as north and south poles

Question 8

what is a hard magnetic material ?

Answer 8

difficult to induce magnetism, but keeps it permanently

steel for example

Question 9

what is a soft magnetic material ?

Answer 9

easy to magnetise, loses induced magnetism quickly
iron for example
adding soft iron core to solenoid increases strength of magnetic field

Question 10

explain how a motor turns

Answer 10

current flows in a wire
creates magnetic field 
field interacts with permanent magnets 
creates a force on the wire
use Fleming's rule to find force direction

Question 11

what the fingers represent on FLHR

Answer 11

first finger = field
thumb = motion
centre finger = current

Question 12

what is the direction of current

Answer 12

+ve to -ve

Question 13

what is the direction of field lines

Answer 13

north to south

Question 14

what is electromagnetic induction?

Answer 14

creation of voltage in a wire which is experiencing a change in magnetic field

Question 15

what are the factors which speed up an electric motor ?

Answer 15

more current
more turns on coil
stronger magnetic field
add a soft iron core

Question 16

how do loudspeakers work ?

Answer 16

A.C electrical signals are fed to a coil of wire in the speaker which is wrapped around base of cone
coil surrounded by perm magnet so force created and makes cone vibrate

Question 17

what is the dynamo effect ?

Answer 17

using EI to transform kinetic energy into electrical energy for example :
electrical conductor moves through magnetic field
or changing magnetic field through a conductor

Question 18

what would you use an ammeter for in the dynamo effect ?

Answer 18

show magnitude and direction of current

Question 19

how to reverse induced current/voltage in dynamo effect ?

Answer 19

reverse movement direction

Question 20

how to get a bigger voltage from dynamo effect ?

Answer 20

increase magnet strength
speed of movement
number of turns on coil

Question 21

how do transformers work ? (5mrk)

Answer 21

Alternating current causing changing magnetic field in soft (easily demagnetised) iron core. Changing magnetic field induces current. Step - up used to boost voltage and step - down used to reduce voltage

Question 22

difference between coils on step up/down transformers

Answer 22

step - down has more coils on primary

step - up has more on secondary

Question 23

transformer coils equation

Answer 23

Vp / Vs = Tp / Ts

Question 24

transformers are nearly 100% efficient so …

Answer 24

Voltage 1 x Current 1 = Voltage 2 x Current 2