Download Electricity and Magnetism

Electricity and Magnetism
Materials can become electrically charged
Electrical charge is a property of matter.
Objects can have a positive, negative, or neutral charge. A proton has a ____positive_____________________ charge, a
neutron has a ____neutral___________and an electron has a _______negative________ charge. Electric charge is
measured in a unit called ______coloumbs_______________________.
Two objects with electric charge exert an electric force on each other. Electric force can be exerted even if the
objects are separated by empty space. The amount of force is greater if the charges are
_____greater________________________ and less if the distance between the objects is _________great____________________ .
Like charges, such as two positive charges, will repel each other, while unlike charges will attract each other.
_______Neutrally______________________ charged objects do not exert an electric force on each other.
The space around a charge where an electric force can be exerted if another charged particle is present called
an electric field.
Static charges are caused by the movement of electrons.
Objects that have equal numbers of electrons and protons have a neutral, or zero, charge. An object with more
protons than electrons have a ______positive_______________________ charge. An object with more electrons than
protons have a ______negative_______________________ charge. The greater the imbalance, the greater the charge an
object has. In most cases, it is the movement of electrons that causes an object to gain static charge.
- Charging by contact occurs when electrons move because materials are touching. In this case, one material
attracts electrons more strongly than others.
- Charging by induction occurs when a charged object produces a temporary movement of electrons in
another object. This movement creates a temporary charge imbalance within the object.
Charges can move from one place to another
Static charges have potential energy
A charged object held near another charged object has potential energy. Just as a rock falls to the ground when it is
let go, one charge will move toward or away from another charge if it is not fixed in one place. A proton placed near
a charged object will have a certain amount of potential energy due to its position.
The electrical potential of a charged object is the potential energy per unit charge that another charge would have
if it were in the object’s electric field. EP is measured in ______volts_______________________ .
The difference in the electric potential at two different points is called the voltage between those two points. If there
is a path for the charges to follow, they will move from _____higher________________________ potential energy to a
______lower_______________________ potential energy.
Materials effect movement
Electrical resistance is a measure of how easily charge moves through a material. Resistance is measured in
_____ohms________________________ . Resistance depends on the size, shape, and type of material.
-charge moves easily through a conductor.
e.g. 1. steel
2.
copper
3. aluminum
-charge does not move easily through an insulator.
e.g. 1. plastic
2.
rubber
3. paper
-superconductors have almost no resistance at extremely low temperatures.
Electrical current is a flow of charge
If a constant potential difference, or voltage, is maintained between two points and there is a path along which
electrons can move between those two points, electric current results.
1. How do positive and negative particles interact?
Positive and negative particles attract one another.
2. Explain what happens when you get a static electric shock as you touch a doorknob.
Your body builds up a charge. As your hand nears the doorknob, an opposite charge is induced
in the doorknob. The charge moves and shocks your hand.
3. Object A has a positive charge. After object A touches object B, A still has a positive charge
and the same amount of charge. What can be inferred about the charge of object B?
That it must have the same charge as object A.
4. Could the same material be both an insulator and a conductor? Explain your answer.
Yes! A material with relatively low resistance would resist the passage of a weak charge but
allow the passage of a strong charge.
Charge needs a continuous path to flow
Electric charge flows through a loop.
A circuit is a closed _______path______________________through which a charge can flow. It has at least four basic parts.
voltage source :provides electric potential
e.g. battery
conductor
:provides connecting path
e.g. wire
switch
:closes or opens the path
e.g. on/off button
electrical device :changes electrical energy into other energy forms
e.g. light bulbs
Circuits make electrical currents useful
Circuits are constructed for specific purposes.
Circuits are designed to be used for specific purposes, such as lighting bulbs, moving motors, and performing
calculations.
Circuits can have multiple paths
In a series circuit, current follows a single path.
-Every element in a series circuit must be functional, or the whole circuit ________stops
working____________________________________.
-Every resistor added to a series circuit ______reduces_____________________________ the current available to each resistor.
-The voltages of batteries in series add together.
In a parallel circuit, current follows multiple paths
Series Circuit- each device is wired on a _______single______________________ path
Draw a series circuit below
-If an element in a parallel circuit is not functional, the other elements still work.
-Every device on a parallel circuit gets full current.
-The voltages of batteries in parallel do not add together.
Parallel Circuit- each device has its ________own_____________________ connection to the
______voltage_______________________ ________source_____________________.
Draw a parallel circuit below.
Circuits convert electrical energy into other forms of energy
Circuit elements can convert electrical energy into other forms of energy. They make electrical energy useful.
1. Explain how a circuit can perform a specific function.
Circuits perform the function of the electrical device, i.e. blowing air, blending food, providing
light, etc.
2. How are series and parallel circuits similar? How are they different?
similar: both have the same parts, same purpose.
different: series: less wire, one goes out all devices go out, on one path. Parallel: more wire,
devices can work independently, several paths.
3. Describe three electrical appliances that use circuits to convert electrical energy into other
forms of energy. What forms of energy do they take?
Answer will vary. E.g. stored potential energy will turn into kinetic energy in a fan: stored
potential -> electrical energy -> kinetic energy
4. You walk past a string of small lights around a window frame (think Christmas lights). Only
two are burned out. What type of a circuit is it, and how do you know?
Parallel, b/c if they are a series, they would all be burnt out as they are on the same path.
Magnetism is a force that acts at a distance
Magnets attract and repel other magnets
The attraction between the north pole of a magnet and the south pole of another magnet is based on the magnetic
field lines that go from the north to the south pole of a magnet.
Define magnet: An object that attracts certain other materials.
Define magnetic field: the region around a magnet where magnet exerts its force.
-if two like poles are placed near each other, the magnetic fields oppose, and the poles ________repel_____________________
each other.
-if opposite poles are brought near each other, the magnetic fields goes from one magnet to another, and the poles
_______attract______________________ each other.
Some materials are magnetic.
Of all the common elements on the periodic table, only ____iron_________________, _____nickel________________,
_____cobalt________________, and a few other elements are actually magnetic. All other materials, such as steel, are only
magnetic because they have _______traces______________ of these other elements.
Earth is a magnet
Because the north pole of a suspended magnet always points in a northerly direction on Earth, it can be inferred that
Earth itself is a magnet. Because it attracts the north pole of a magnet, however, the magnetic north pole of Earth is
actually the _____South________________pole of the magnet formed by Earth.
Current can produce magnetism
An electric current produces a magnetic field
Both permanent and temporary magnets result from the magnetic field formed from a moving electric charge.
-
Permanent magnets result from the spinning of unpaired electrons, which are electrically charged particles.
Temporary magnets can also be formed in this manner, but the magnetic domains don’t remain aligned.
Temporary magnets know as electromagnets are produced by electric current, which consist of
______electric_______________________ charge.
In the electromagnet below, coils of wire around an iron core create a magnet as long as electric charge flows. When
current stops, the magnetism stops.
Motors use electromagnets
The basic parts of an electric motor are a voltage source, a shaft, a commutator, an electro-magnet, and at least one
additional magnet.
-Forces of repulsion between the two magnets turn the shaft.
-The commutator reverses the poles of the electromagnet when it starts to align poles of the electromagnet.
-This reversal renews the repulsion force and keeps the shaft moving.
Magnetism can produce current
Magnets are used to conduct an electric current.
Essentially, a generator is the opposite of an electric motor. The motor uses a moving
___magnets__________________ to produce a magnetic field and a generator uses a moving magnet to produce an
electric charge.
-The magnet and the wire through which the current passes must be moving relative to each other. It doesn’t
matter which one moves, as long as one of them does.
-The current produced can be either direct current, which flows in one direction only, or alternating current,
which changes direction at regular intervals.
Magnets are used to control voltage
A transformer either ___increases__________________or _____decreases________________voltage. In a transformer, two
coils of wire are wrapped around an iron ring. Current through the first coil causes the ring to become an
electromagnet. This electromagnet induces a current in the second coil.
-If the first coil has more loops, the voltage ___decreases__________________, and the system is a step-down
transformer.
-If the first coil has fewer loops that the second coil, the transformer is a step-up transformer and voltage
_____increases________________.
1. What force causes magnets to attract or repel one another?
The force of magnetism
2. Is magnetism a physical property or a chemical property? How do you know?
PHYSICAL- nothing changes by testing this property
3. Why are some materials magnetic, while others are not?
Because of the arrangement of their electrons and magnetic domains.
4. A needle is picked up by a magnet. What can you say about the needle’s atoms?
The magnetic fields of the atoms are aligned.
5. Hundreds of years ago, sailors observed that as they traveled farther north, their compass
needle tended to point toward the ground as well as toward the north. What can you
conclude about the magnet inside Earth form this observation.
The magnetic poles are within the Earth, not at the surface.