Static Electricity Flashcards
What is electricity
Electricity is the flow of electrical charges - it is the result of the movement of electrons.
It is the main form of energy used today.
NO NET CHARGE =
Matter with an equal number of protons and electrons.
Some energy sources used to make electricity are:
hydro dams
solar
coal
natural gas
wind
nuclear energy
Where does an electrical charge come from?
Each electron and each proton carries a tiny amount of electrical charge.
A net electrical charge comes from the imbalance of protons and electrons
Positive (+)
a positive charge occurs when there are more protons than electrons.
Negative (-)
a negative charge occurs when there are more electrons than protons.
Nucleons
The particles in the nucleus of atoms, protons and neutrons, are called nucleons.
Nucleons are what give an atom its identity (6P = carbon, 19P = K ,etc).
Nucleons are BIG when compared to electrons.
When it comes to electricity, nucleons DO NOT move.
Electrons
These particles are much smaller and lighter than nucleons
They are able to move from atom to atom in some materials.
They are responsible for the electrical phenomena we will be studying.
Measuring electrical charges
In lab experiments and everyday life, we cannot really notice and measure the effect of a single electron’s charge; it is too small (certain experiments can).
It is more common to measure the charge of large groups of displaced electrons. One coulomb contains many MANY electrons!
Charge of a proton
A proton has a positive charge of 1.60 x 10-19 C
Charge of an electron
Electrons have a negative charge of - 1.60 x 10-19 C
Unit
UNIT: coulomb ( C )
How many electrons are in 1 Coulomb?
Remember, one electron has a charge of (negative) 1.60 x 10-19 C.
x = 6.25 x 10 18 electrons
How much charge is contained in an object that has gained 3.2 x 1012 electrons?
Positive 3.52 x 10-5 C
How much charge is contained in an object that has lost 500 000 000 electrons?
negative 1.15 x 10-10 C
An object is found to have a net charge of -3.2 x 10-4 C. How many electrons were transferred IN or OUT of the object?
2 x 10 15
Electrical forces
When two charged objects come in close proximity to each other an electrical force is created.
If the objects are of opposite charge, the electrical force will pull them towards each other.
If the objects are of the same charge, the electrical force will push them apart.
TWO TYPES OF ELECTRICITY
static and dynamic
Static electricity
This is called static electricity because it is about stored, non-moving charges.
CHARGING OBJECTS
Most object are neutral (# of e- = # of p+)
For an object to become charged a transfer of e- must take place.
An object is deemed ”charged” when it has an unequal amount of positive and negative charges.
Objects can be positively or negatively charged. It is always via gaining or losing valence electrons that an object becomes charged.
FRICTION
Charging by rubbing (one material “likes” electrons more than another material and “takes” the electrons when they are rubbed)
CONDUCTION
Charging by contact (excess/deficit of electrons is shared between the objects in contact)
INDUCTION
Charging without contact (bringing a charged object close to another cause the uncharged object to become temporarily charged)
Friction procedure
Start with: two neutral objects made of different materials
One “likes” electrons more, and will take them from the
other object (See table)
Finish with: two oppositely charged objects
CHARGING BY CONTACT/CONDUCTION
procedure
Start with: one charged object, one neutral object
When the objects touch, the surplus (too many, negatively charged object) or lack (too few, positively charged object) of electrons is shared among the two objects
Finish with: two objects with same charge (each is less charged than the initial object: the initial charge is shared).
When conductive objects touch, as far as the electrons are concerned, the two objects essentially become one.
Excess (or lack of) electrons is spread out inside the new bigger object.
Each part of the object gets charged equally (depends on how conductive)
The initial charge is now shared among the 2 objects.
When you separate them, each retains the new excess/lack of electrons, which is less than the initial.
CHARGING BY INDUCTION
procedure
Start with: one charged object, one neutral object
When the charged object is brought close to the neutral object, the electrons in the neutral object are either attracted or repelled by the charged object
The electrons in the neutral object become unevenly distributed, giving the appearance of opposite charges on each side of the neutral object
If you remove the charged object, the electrons in the neutral object redistribute themselves evenly over time
Conductors and insulators
Most objects are neutral (# of e- = # of p+)
Charging an object = transferring e- from one object to another
Depending on how an object reacts to the transfer electrical charges,
Conductors
Permits the free flow of electric charges
Ex: metals and electrolytic solutions
Typical conductors
Silver
Gold
Copper
ALuminum
Mercury
Steel
Iron
Seawater
Concrete
Platinum
Brass
Bronze
Graphite
Insulators
Impedes the free flow of electrical charges
The charges do not move well
Ex: Non metals (wood, plastic, glass, paper, ceramics …)
3 groups
we classify them in 3 groups
Conductors
Semiconductors
insulators
Semi conductors
Semiconductors
Used in electronics
Ex: Metalloids, carbon
Typical insulators
Glass
Plastic
Ceramic
Rubber
Wood
Fabric
Paper
Wool
Cork
ELECTRIC FIELD
A charged object has an influence on the space around it.
Faraday imagined this influence as invisible tentacles. Today we visualize the electric field as “lines” that radiate from charges.
The arrows always go from positive to negative.
(Electric field line arrows are drawn to show how an imaginary positive test-charge would move. Like charges repel, opposite charges attract.)
Coulomb’s Law
Measures the electrical force between charges
Greater charge = greater the force
Greater distance between charge = weaker the force
No need to memorize the formula or the constant it is given. You do need to know the units for electrical force, charges, and distance
Fe = kq1q2
r2
Fe = electrical force (N)
k = coulomb constant (9 x 109 Nm2/C2)
q1 and q2 = charge of particles (C)
r = distance between particles (m)
ELECTRICAL FORCE
The electric force a charge experiences depends on it’s own charge (q1), the charge on the other object (q2), and the distance between the charged objects (r).
q1 and q2 are measured in Coulombs (C)
r is measured in meters (m)
k is a constant and has a value of 9x109 Nm2/C2
