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 loudspeaker

Answer 10

-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 11

generator effect

Answer 11

-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 12

simple ac generator

Answer 12

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

Question 13

difference between dc and ac

Answer 13

dc- direct current, flows in one direction
ac-alternating current, changes direction

Question 14

moving coil microphone

Answer 14

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

Question 15

the faster the coil rotates

Answer 15

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

Question 16

traditional transfromer

Answer 16

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

Question 17

switch mode transformer

Answer 17

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

Question 18

transformers

Answer 18

-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 19

step up transformer

Answer 19

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

Question 20

step down transformer

Answer 20

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

Question 21

the higher the grid…

Answer 21

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

Question 22

what is a magnetic field

Answer 22

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

Question 23

the size of the induced potential difference increases when

Answer 23

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

Question 24

step up and step down transformers

Answer 24

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

Question 25

how does a transformer work

Answer 25

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

Question 26

mains supply into home’s

Answer 26

230V

Question 27

current produced in a typical power station

Answer 27

25000V

Question 28

what range of frequency does a switch mode transformer operate by

Answer 28

50kHz to 200 kHz