Magnetic Effects of Current HOTS 2

Question 1

what is the si unit of mag field strength

Answer 1

it is a vector quantity
si unit: tesla
1 tesla=1N/amp.metere
cGS: Gauss
I tesla= 10⁴ gauss

Question 2

what happens when a magnet is cut in half into in transverse/along length

Answer 2

bothcases new magnets produced
i)transverse
pole strrength same, mag moment changes

ii)length
pole strength and mag moment changes

mag moment refers to the force experienced by a magnet in an external magnetic field

Question 3

a freely suspended magnet always aligns in the north south direction

Answer 3

earth is a huge magnet with its south pole lying somewhere near the geographical north and north pole lying somewhere near the geogpahical south

Question 4

why are magnetic field lines closed continuous curves?

Answer 4

mag poles always exist in pairs. Ourside the magnet the directionof fied is from north->south. Inside it its from south->north, forming endless closed loops

Question 5

give the uses of compassneedle

Answer 5

-plot the magnetic field around a bar magnet
-navigation of ships
-finding the posn of electrical wires in the walls whic are closed

Question 6

define magnet? what are natural artificial magnet

Answer 6

magnets are subtances that have the property to attract fe,ni,co.

natural magnets are made of lodestone(fe3o4).
Since they have an irregular chape, pieces of iron and other magnetic materals are made to acquire natural magnetic properties and can be made to take a diff shape.
shapes: bar magnet/horshoe/circular/needke

Question 7

name and explain the components of domestic electric circuit

Answer 7

i)Live wire and neutral wire: maintain p.d because live wire carry 220v of current and neutral wire 0V

ii)earth wire: safety measure protects us from severe chosk from casing of appliances

iii)Fuse:safety measure whenever current exceeds permissible limit, the fse melt and break the circuit

iv)electric meter records amount ofellectrical energy used

v)distrubution box several independent distrubution circuits are drwn to different parts of the house

vi)two seperate circuits- one is 5A circuit for lighter applieances lieke tubelight
-one is 15a circuit for heavy applieances with high power rating

Question 8

what is snow rule and snbe rule?

Answer 8

SNOW
if current is from s-north and the wire is over compass needle, the head of needle deflects towards the west

SNBE
if current is from n->s ad the wire isbelow the compass needle, the head of needle deflects east

Question 9

A current through a horizontal power line flows in east to west
direction. What is the direction of magnetic field at a point directly
below it and at a point directly above it?

Answer 9

The current is in the east-west direction. Applying the right-hand
thumb rule, we get that the magnetic field (at any point below or
above the wire) turns clockwise in a plane perpendicular to the wire,
when viewed from the east end, and anti-clockwise, when viewed
from the west end.

Question 10

give reason: why a coil of a smaller radii has a greater magnetic field

Answer 10

snaller radii will be more field fo the same magnitude of current because b inversely proportional r(radius)

Question 11

justify that B=n x b

Answer 11

Since the same current flows in the same direction produces the same magnetic field, the mag field produced due to each turn becomes additive

Question 12

justify the mag field produced at centre of a coil of n turns is as large as produced by a single turn

Answer 12

i) the mag field lines near the wire are almost concentric circles
ii) as we move to the centre of the circle, the concentric circles become larger and larger. Near the centre, these arcs appear as parallel straight lines.
iii) near the centre, the magnetic field becomes almost uniform. So in a current carrying loop, the magnetic field arein the same direction and are very strong at centre.

Question 13

what is the magnetic field in the middle of current carrying circle

Answer 13

it is 0 because the fiels are opp and equal

Question 14

what happens when two parallel straight conductors are carrying current
i)in opp direction
ii) in same direction

Answer 14

i) they repel because mag field is in same direction
mag field at centre is very strong coz mag field is additive
ii)they attract because the mag field is equal and opp
mag moment is 0 at centre

Question 15

what does a strength of electromagnetdepend upon?

Answer 15

i) directly proportional to n nuber of turn
ii) direclty proportional to i magnitude of current
ii)i)inversely proprotional to air gap. lesser air gap more strength

Question 16

how to make a en electromagnet

Answer 16

i) take 10 iron nails
ii)tightly wound copper wire on it
iii)connect the ends of the wire to the two terminals of the battery with a key.
iv)plug in the key

Question 17

why is ironc ore better than steel to prepare an electromagnet?

Answer 17

i)steel retains magnetic property and becomes a permanent magnet even when current is switched off. it is becuase stell gets parallel of e-s in effect of curent and remains
ii)however soft iron core loses its magnetic properties when the current is wtiched off and hence mag field is temporary. Iron gets the llel oreintatiin of e-s and goes back to zigzag when current is stopped causing it to cancel the charge and make net 0.

Question 18

how is the magnetic field in our body used in mri?

Answer 18

Two main organs in the human body where
the magnetic field produced is significant, are the heart and the brain. The magnetic field
inside the body forms the basis of obtaining the images of different body parts. This is
done using a technique called Magnetic Resonance Imaging (MRI). Analysis of these
images helps in medical diagnosis.

Question 19

is there a magnetic field near our nerve cells

Answer 19

An electric current always produces a magnetic field. Even weak ion currents that
travel along the nerve cells in our body produce magnetic fields. When we touch
something, our nerves carry an electric impulse to the muscles we need to use. This
impulse produces a temporary magnetic field. These fields are very weak and are about
one-billionth of the earth’s magnetic field.

Question 20

what makes aquatic animals survive? swim in the ocean

Answer 20

aqutic animals have natural lodestone in them, such tiny magnetic field intercepts the earth’s mag field allowing them to go deeper.

Question 21

what are uses of permanent magnets

Answer 21

microphone,ammeter,voltmeter,geenrator,motor,fridge door

Question 22

how can permenant magnets be demagnetised

Answer 22

i)heating them
ii)dropping continuously from a reasonable height
iiii)improper storing
iv)hammering

Question 23

when do we get a force experienced by particles? explain the diff conditions

Answer 23

F=qvBsinθ

the particle must be charged, if q=0 then f=0

the charged particle must be moving with a velcotiy if charged particle is at rest then v=0,then F=0

there must be a definite magnetic field. B must be there, if B=0 then F=0

angle theta is the angle between the direction of the moving charged particle and the direction of magnetic field. If theta=90 then sin90=1, the force is maximum. If theta=0/180, sin0=0 then force =0. the particle must not be parallel nor antiparallel.

Question 24

a charged particle in an external field experiences a force? where is this used?

Answer 24

This force is used to accelerate charged particles. EX: van de graaf generator, used to bombard and study the atomic nucleus/tv picture tube

Question 25

explain the importanc of earth magnetic field

Answer 25

Earth magnetic field saved us from the ill effects of high energy charged particles coming from the un in the form of solar winds. The earth magentic field deflects these particles away from the surface of the earth. These are trapped near the earth magnetic equator. These are called Van Allen Radiation Belts.

Question 26

List two methods of producing magnetic fields

Answer 26

->permanent magnet
-> current carryoing conductor/solenoid
->electromagnet

Question 27

How does a solenoid behave like a magnet? Can you determine the north and
south poles of a current–carrying solenoid with the help of a bar magnet? Explain.

Answer 27

->mag field in a soleond and br magnet are very similar
-> inside the solenoid, the mag field is strong and uniform.
-?like a bar magnet the ends of a solenoid behaves like the 2 poles of a bar magnet one south and one north
-> we can find thepolarity of solenoid using bar magnet.
->the norht pole of the magnet when it gets attracted to soelnoid means south polarity other is north
->if the north pole of the magnet get repelled by the solenoid, then it has north polairty
-> it behaves like a magnet only when current is passed.

Question 28

why does a current carrying conductor kept in a magnetic field experience force? what is the direction of force acting on the conductor?

Answer 28

• a current carrying conductor consists of freely moving negatively charged electrons.
• these charged particles,when passing through an external magnetic field, experience a force which is
  F=Bev(v is velocity of the moving particles)
• the total force experienced by the electrons is equal to the force experienced by the conductor.
• the direction of force acting is perpendicular to direction of mag field and current.

*the directionof force is determined by fleming left hand rule.

Question 29

what is magnitude of mag fied

Answer 29

The force acting per unit current per unit length of a current carrying conductor placed perpendicular ot the mag field.