Download PPT Notes Circuits and magnetism-13

Types of Circuits
What is the difference between the wiring?
1
Series Circuits
The light bulbs turn on.
1V
0.5 V
Battery
is 1.5 V
+
However, since the
voltage drops, the
lights are dimmer.
2
Series Circuits
If this light bulb does not turn on,
Burned out light bulb
This is because the
circuit is broken here;
neither light bulb
will turn on.
so the current can’t flow
to this bulb here.
Battery
is 1.5 V
+
Christmas lights are commonly made this way.
3
Series Circuits Info
• The current has only one path it can travel along
• One light goes out all lights out-open circuit
• Imagine if you turned off one light in your house that
means that the circuit is broke and everything else goes
off. Everything would have to be turned on to keep
things running.
• Current is the same at all points
• Voltage is reduced by each resistance (light bulb,
motor, heaters)
• Voltage drop-each separate resistor causes volts to
drop
4
Kirchhoff’s Voltage Law
•The total of all voltage drops must add up
to the total voltage supplied by the
battery. (energy in)
•+1.5 V - 0.5V - 0.5 V - 0.5 V = 0
battery bulb bulb bulb
5
Parallel Circuits
- a divided circuit and the current has more than one path.
+
6
Parallel Circuits
When one light bulb burns out the others still light up.
Even though the path is
stopped, the other light
turns on because its
circuit is not broken.
+
Burned out
light bulb
Your house is wired with parallel circuits.
Why do you think this is so?
7
Parallel Circuit Info
• contains separate branches for current to move through
• potential difference (volts) same at each branch
• one light off, use other branches to transfer current
• voltage is the same across all branch points (think of
them as separate series circuits connected to a battery)
• each branch does NOT always have the same current,
depends on how much resistance is in each branch, (desk
lamp, power saw)
8
Kirchoff’s Current Law
• If current flows into a branching point, the same
total current must flow out again.
9
MAGNETISM
• property of
matter in which
there is a force of
attraction or
repulsion
between unlike
or like poles.
10
MAGNETIC MATERIALS
1. Permanent magnet
• material that keeps its magnetic properties,
even when it is not close to other magnets
• Magnetite = natural magnetic rock
(Lodestone)
• Ex. bar magnet, refrigerator magnet, horseshoe
magnet
2. Temporary magnet
• easy to magnetize, quick to lose magnetism
• nickel, cobalt, iron, eg. AlNiCo (alloy)
11
Common Properties of
Magnets
• Two opposite poles called north and south
• If divided, there will always be a north and
south pole
• When near each other, magnets exert
magnetic forces on each other
• OPPOSITE POLES ATTRACT; LIKE POLES
REPEL
12
Magnetic Domains
•Domains-groups of atoms with aligned magnetic poles
•Electrons in atoms behave like small loops of current that
act like tiny electromagnets with north and south poles
•We don’t see the magnetism because it is so small and on
average the atomic magnets cancel each other out
•When atoms are aligned in a similar direction a permanent
magnet is produced
•Atoms in iron, cobalt, and nickel are free to move - If
brought near a permanent magnet it forces the atoms to
temporarily align and therefore becomes a temporary
magnet
•In nonmagnetic materials the atoms are not free to move
so they are not affected by magnets
13
Magnetic Domains
unmagnetized
magnetized
14
Auroras
• NORTHERN &
SOUTHERN LIGHTS
• Produced by the earth’s
magnetic field trapping
charged particles from
the sun.
• The particles collide
producing light.
15
Losing Magnetic Properties
Magnets lose their magnetic properties
if alignment of the domains is
destroyed.
Alignment can be destroyed by:
1. dropping the magnet
2. heating the magnet
16
Magnetic Fields
• The force felt around the area of the magnet
• Magnetic field lines – represent the direction of
the field around a magnet; Arrows are drawn north
to south
• Number of field lines represents the strength of the
magnet in that area
• The force is the strongest at the poles
17
Discovering Magnetism
• 500 B.C. – people discover naturally occurring
materials have magnetic properties (lodestone which is
magnetite)
• 500 B.C. – Greeks noticed one end of suspended
lodestone pointed north and the other pointed south, first
application of the compass
• 220 B.C. – Chinese also recorded use of compass called
“south pointer”
• 1088 A.D. – Chinese made small needle like compass
• 1183 A.D. – modern compass appears
18
Compass
Compass needle is a
magnet free to spin
until it lines up in the
north-south direction
Geographic north pole of
the Earth is the
magnetic south pole
since it attracts the
north poles of the
magnet
19
EARTH’S MAGNETIC FIELD
20
Do you know where the North
Pole Is?
Wandering Pole
While the Magnetic
Pole often skips
around many miles
each day in an oval
loop, on average it
migrates from 6 to 25
miles each year to the
north/northwest.
21
Movement of the Pole
• During the
sixteenth century,
mariners believed
that somewhere
in the North was
a magnetic
mountain that
was the source of
attraction for
compasses.
22
23
ELECTROMAGNETISM
• Hans Christian Oersted
– Danish physicist and
chemist who discovered
that a current in a wire
caused a compass
needle to deflect
• Moving electric charges
create a magnetic field
24
Electromagnet
•Magnets that are created when there is electric current
flowing in a wire
 Simplest electromagnet uses a coil of wire, often wrapped
around some iron
 Iron core becomes a magnet
 Magnetic field aligns with the coil carrying current
 North and south poles are located at the end of each coil
 Which end is north depends on the direction of the electric
current (North is where the current comes out)
 A good electromagnet is a balance between too much
resistance and having enough coils to get a strong magnet
•Uses of electromagnets – speakers, doorbell, toaster
25
ELECTROMAGNET
26
INCREASING THE STRENGTH
1) increase size of iron core
2) increase current
3) increase the number of coils
27
ELECTROMAGNETIC
INDUCTION
• 1831 - Michael Faraday(UK) & Joseph Henry(USA)
• process by which moving a wire through a magnetic
field an electric current is induced in that wire
• If a magnet is thrust into a coil it induces current flow
• If the magnet stops the current stops
• The quicker the movement of the magnet the more
current induced
• When you pull the magnet back out the current flows in
the opposite direction
• Electromagnetic induction is how we transform
mechanical energy into electrical energy
• Power plants use generators
28
• Generators change mechanical energy to
electrical energy
• Electric motors changes electrical energy into
mechanical energy
• Commutator-reversing switch in a motor that
rotates with an electromagnet
29
ELECTRIC MOTOR
30
GENERATOR
31
• Transformers:
step-up (increase) or step-down (decrease)
voltage
• MRI-magnetic resonance imaging-magnetic
field taking pictures of your insides
32
MRI uses radio waves and a
magnetic field to produce images of
the body
33
Electrical Measuring
Instruments
• Voltmeter-used in parallel to measure
voltage
• Ammeter-used in series to measure
current
• Galvanometer-use to detect a current
34
New uses for magnetism
35