chapter 15- motors, generators and transformers

Question 1

magnetic materials

Answer 1

iron steel cobalt nickel

Question 2

which way do magnetic field lines go

Answer 2

north to south

Question 3

the closer together…

Answer 3

the stronger the magnetic field

Question 4

how do compasses show the direction of magentic field

Answer 4

-compasses will point in direction of magentic field
-when not in a magnetic field they will always point north

Question 5

permanent magnets

Answer 5

have their own magnetic field

Question 6

induced magnets

Answer 6

magnetic materials that turn into magnets when they are put into a magnetic field

Question 7

how do you increase the strength of a solenoid

Answer 7

-increase loops
-increase current
-put an iron bar inside the solenoid

Question 8

the motor effect

Answer 8

when a current carrying wire has a magnetic field. When current carrying conductor is placed in a magnetic field, so that it cuts line of magentic force, the magnet and the confuctor exert a force of eachother.

Question 9

in the motor effect the force is:

Answer 9

-increased if the current or strength of MF is increased
-at right angles to the direction of the magnetic field to the wire
-reversed if the direction of the current or MF is reveresed
-zero if the wire is parallel to the magnetic field

Question 10

motor effect coil of wire

Answer 10

-there is a magnetic field and current in a wire, causes a magentic field
-two fields interact giving a resultant force on the wire
-current in opposite direction in each side of the coil, causes the coil to spin
-forces act in oppsite direction on either side of the coil

Question 11

motor effect loudspeaker

Answer 11

-current creates a magnetic field around the coil
-which interacts with the permanent magnet
-producing a resultant force causing the coil/cone to move
-when the direction of the current reverses, the direction of the resultant force reverses, producing a sound wave

Question 12

motor effect one wire

Answer 12

-a motor converts electrical energy to mechanical energy
-current in the wire creates a magnetic field around the wire
-there are now two magnetic fields, one from the permanent magnet and one from the current carrying wire
-two fields interact or combine giving a resultant force on the wire

Question 13

generator effect

Answer 13

-effect of inducing a potential difference across the ends of a conductor using a magnetic field
-when a conductor moves relative to a magnetic field (cuts through), the conductor is in a changing MF

Question 14

simple ac generator

Answer 14

made up of a coil that spins in a uniform magnetic field

Question 15

simple dc generator

Answer 15

has a split- ring commutator instead of two slip rings

Question 16

moving coil microphone

Answer 16

sound waves make the coil vibrate in the magnetic field, so a varying p.d is induced

Question 17

the faster the coil rotates

Answer 17

-the greater the frequency (number of cycles per second) of the alternating current
-the larger the peak value of the altnerating current

Question 18

traditional transfromer

Answer 18

-works only on a.c, because changing magnetic field is necessary to induce a.c in the secondary coil

Question 19

switch mode transformer

Answer 19

-lighter and smaller than an ordinary transformer, operate at high frequency

Question 20

transformers

Answer 20

-change the p.d but only on alternating currents
-they all have 2 coils of wire, the primary and secondary, joined with an iron core
-when an alternating pd is induced across the primary coil, the iron core magnetises, and demagnetises, induces changing pd in the secondary coil
-if the second coil is part of a complete circuit, this causes a current to be induced

Question 21

step up transformer

Answer 21

-makes the pd acorss the secondary coil higher than the pd acorss the primary coil, secondary coil has more turns than primary coil

Question 22

step down transformer

Answer 22

makes the pd across the secondary coil lower than the pd on the primary coil, secondary coil has fewer turns than primary coil

Question 23

the higher the grid…

Answer 23

potential difference, the greater is the efficiency of transferring electrical power through the grid

Question 24

what is a magnetic field

Answer 24

region of space around a magent where a magentic material will experience a force

Question 25

the size of the induced potential difference increases when

Answer 25

-speed of the movement increases
-strength of magnetic field increases
-number of turns on coil increases
-area of coil increases

Question 26

step up and step down transformers

Answer 26

increase the voltage before the distrubution lines and reduce it at the end to produce a safer voltage for local consumers

Question 27

how does a transformer work

Answer 27

-alternating current induced in primary coil
-induces changing magnetic field in iron core
-induces alterntaing pd in secondary coil

Question 28

mains supply into home’s

Answer 28

230V

Question 29

current produced in a typical power station

Answer 29

25000V

Question 30

what range of frequency does a switch mode transformer operate by

Answer 30

50kHz to 200 kHz