Electrostatics Flashcards
What is a proton?
Positively charged
What is a electron?
Negatively charged
What is a neutron?
Neutrally charged
Objects are charged by….
Adding or removing electrons (not protons).
When does the positive charge occur?
When there are fewer electrons than protons.
When does the negative charge occur?
When there are more electrons than protons.
Opposite charges…
Attract
Like charges…
Repel
What is the Law of Conservation of Electrical Charge?
If one region or object acquires a positive charge, then an equal amount of negative charge will be found in neighboring regions or objects.
Law of Conservation of Electrical Charge’s net amount
The net (sum) amount of electric charge produced in any process is zero
What is a conductor?
A substance that allows electrons to move easily from one atom to another. Ex: silver, copper, and aluminum.
What is an insulator?
A substance that does not let electrons to move freely from one atom to another. Ex; plastic, cork, or rubber.
1-3 valence electrons
Conductor
5-8 valence electrons
Insulator
What is an Electroscope ?
An instrument used to detect the presence of an electrostatic charge.
2 Types of Electroscope
Pith Ball Electroscope and Metal Leaf Electroscope
Metal Leaf Electroscope
Leaves separate when a charge is present.
Charging by Friction
Two substances are rubbed together. The electrostatic series indicates the sign of the charge for each of the two substances.
Charging by Conduction (Contact)
A charged object touches another object; the amount of charge equally divide between the two objects if they have the same geometry. The same sign charge is acquired by each object.
Induction
A charged is brought near, but not touching, another object.
It has a charge separation (called polarization)
Induction
The two objects end up with opposite charges.
Induction
Polarization
Occurs when particles in an insulator realign themselves because a charged object is brought near.
Example: Charging a balloon and sticking it to a wall.
Polarization
Coulomb’s Law
Calculates the electrostatic force between the two objects.
1 C = ?
6.24x10^18 Electrons
Equation of Coulomb’s Law
Fe = kq1q2/r^2
K
Coulomb’s constant, or 9 x 10^9 Nm^2/C^2
q
The magnitude (Not the Sign) of charge in coulombs.
r
The distance of separation in meters (this distance is always a center to center.
f
The electrostatic force in Newtons. It is either attractive or repulsive.
The direction of the force is always along a line…..
Joining two objects
If the two objects have the same sign…
The force on either object is directed away from each other.
If the two objects have opposite signs…
The force on either object is directed towards each other.
Elementary Charge
The charge of either an electron or a proton. The charge of a proton is equal in magnitude to that of an electron, but it’s positive.
e = 1.6 x 10^-19 C
Charge of 1 proton or 1 electron
What is an electric field?
The area around a charged object.
What does the electric field exert?
Electrostatic force on any object in its vicinity
Electric field lines
Electric fields are drawn with vectors
Line points towards
A negative charge
Line points away
A positive charge
Stronger field
More and Closer lines
They NEVER cross
Field Lines
The closer the object…
The greater the force
How can we determine if an object has a positive or negative electric charge?
We use a test charge (small positive charged object) to determine the direction of an unknown field.
The test charge would…
Follow the path of the field lines
E
Electric field strength/intensity (N/C)
The force depends only upon the….
The magnitude of the point charge producing the field
The force does not depend upon the..
The value of the test charge
What is a Uniform Electric Field?
A special situation when 2 charged plates (one positive, one negative) are parallel and evenly spaced.
The electric field strength is…
The constant between the plates, except the edges.
Ee
The electric force applied to the charge, in Newtons (N)
Fe = qE
How we determine the strength (or intensity) of the electric field.
What is a magnet?
Something that has a magnetic field around it
Properties of magnets
A magnet has polarity- it has a north and a south pole
Compass Needle
A suspended bar magnet
Un-like poles
Attract
Like poles
Repel
Cutting bar magnet in half…
It would form smaller magnets
Hard Magnets
Difficult to magnetize and holds magnetism longer
Soft Magnets
Easy to magnetize and loses magnetism easily (ex. iron)
Permanent Magnets
Made of metallic alloys, like iron, nickel, cobalt, etc.
Each atom in a material…
Acts as a small magnet
When all magnets are randomly aligned..
There is no net magnetic field
When there is no magnetic field…
The magnet loses its magnetism
Domain theory of magnetism
Ferromagnetic materials have atoms that group together in domains.
Ferromagnets are substances that are attracted to magnets..
Therefore can become a magnet
Atoms within each domain line up their…
Magnetic fields with neighboring atoms
Magnetic fields can cancel
Randomly oriented domains
When unmagnetized…
The domains point in all different directions
When magnetized…
The domains point in the same direction
You can make a temporary magnet by…
Forcing the domains to align. By placing a strong magnet next to the ferromagnetic material.
You can destroy the magnet and make it lose its magnetic field by:
Dropping it or heating it, this forces the domains to become random again
What is a magnetic field?
The area around a magnet that interacts with other magnetic materials.
Magnetic field flows from..
North to South (not positive to negative)
B
Symbol for magnetic field
SI
Unit for Tesla (T)
Can we use a compass for navigation?
Yes and No. A compass will usually point in the general direction of geographic north, which would be helpful if you were lost in the woods.
Unfortunately, for accurate navigation…
Some adjustments are necessary with your compass readings.
The problem with Navigating by Compass
The Earth’s magnetic poles moves slowly over time
Solution #1: Magnetic Declination
Angle between the magnetic South Pole and the geographic North Pole.
Maps are based on geographic North Pole because it does not change over time.
Accurate compass measurements require an adjustment to the compass reading using the Magnetic Declination angle.
Solution #2: Magnetic Inclination
Angle between the horizontal surface of the Earth and the magnetic pole (inside the Earth)
It is measured with a dipping needle.
Electricity have?
Positive and Negative Charges
Eletricity repel when?
Like Charges
Electricity attracts when?
Unlike charges
Electricity field lines flow from
Postive to Negative
Electricity’s Density of lines equals
Strength of E
Electricity’s SI unit
Ampere, 1 A = 1 C/s
Electricity’s E exerts force..
On a charge (E = F/q)
Magnestism have?
North and South Poles
Magnestism repel when?
Like Poles
Magnetism attracts when?
Unlike poles
Magnetic field flow from..
North to South
Magnetism’s density of lines
Equals strength of B
Magnetism’s SI unit
Tesla, 1 T = 1 N/Axm
Magnetism field exerts force…
On a moving charge, B = F/(qv)
In the early 1800s, scientists knew that there were similarities between the electric fields and magnetic fields, but…
Had not discovered any direct relationship between them.
Who determines to find the direct relationship between electric and magnetic fields?
Hans Christian Oersted
How did Christian Oersted determine the direct relationship?
He used a battery, a wire, and a compass needle.
What did Christian Oersted found?
That only an moving current in a wire produced a magnetic field.
What did Oersted showed that could not produce a magnetic field?
Stationary Electric Charges
What can only create a magnetic field?
An Electric Current
During a physics lab, a plastic strip was rubbed with cotton and became positively charged. The correct explanation for why the plastic strip becomes positively charged is that….
the plastic strip lost electrons to the cotton during the charging process.
Your physics teacher has prepared the room for the class’s entry by suspending several inflated balloons from the ceiling. Upon entering the physics room, you observe two balloons being drawn towards each other as shown at the right. The attraction of these balloons for one another provides evidence that ______.
at least one of the balloons is charged; the other is either charged or neutral
Insulators are different than conductors in that insulators ____.
do not allow charge to freely move
The leaves of an electroscope are initially apart from each other. When a charged rod is brought near the electroscope, the leaves get closer together.
The electroscope is initially charged with the opposite polarity of the rod.
A negatively charged rod is brought near a metal can that rests on a wood table. You touch the opposite side of the can momentarily with your finger. The can is then
positively charged
If you comb your hair and the comb becomes negatively charged, your hair becomes
positively charged
A negatively charged rod is brought near an object. The protons in the object move towards the rod, while the electrons move to the opposite side of the object. The separation of the charges are called_____.
polarization
Electrical forces between charges are strongest when the charges are
close together
When the distance between two charges is cut in half, the electrical force between them
Quadruple
Two parallel plates are oppositely charged. The left plate is negative and the right plate is positive. In which direction does the electric field point?
to the left
