Electrical Resistance
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Electrical Resistance: The electrical resistance of a conductor is related to how poorly that conductor allows charges to move though it.
Factors that determine the Electrical Resistance:
1. Types of conductor
-What material is it made of? Metals overall are better than nonmetals and silver has the lowest resistance. If it’s a good conductor , it has a low resistance. If it’s a poor conductor, it has a high resistance.
2. Thickness of Wire
-If you want low resistance, then use a thick wire.
-If you want high resistance, then use a thin wire.
3. Length of Wire
-If you want to lower the resistance then you want the wires to be short.
Resistance Problem
By · CommentsResistance Problem:
Equation needed to solve problem:
Please let me know if this helped.
To your Physics Success
Resistance
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The Resistance (R) is defined as the ratio of the voltage V applied across a piece of material to the current I through the material.
Every conducting material has a certain amount of resistance.
Ohm’s Law: A law stating that electric current is proportional to voltage and inversely proportional to resistance. The ration V/I is a constant, where V is the voltage applied across a piece of material and I is the current through the material.
Resistance Example:
Electric Current
By · CommentsWithin a battery, a chemical reaction occurs that transfers electrons from one terminal to another terminal.
The maximal potential differences across the terminals called the electromotive force (emf).
Electric current is the amount of charge per unit time that passes through a surface that is perpendicular to the motion of the charges.
To calculate the electric current:
Electric Current Tutorial:
Units of Measurement
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System BE CGS SI Length Foot (Ft) Centimeter (cm) Meter (m) Mass Slug (sl) Gram(g) Kilogram (kg) Time Second (s) Second (s) Seconds (s)
test
By · Commentstest
Electric Potential Energy
By · CommentsExample:
I am holding a ping pong ball in my hand up in the air. In this position does the ping pong ball have gravitational potential energy?
Yes, because it is at some height above the ground. The ground being the reference level.
If I let the ping pong ball go, what is going to happen to the ping pong ball?
It is going to fall. Why does it fall? Why does it fall downwards and not rise upwards?
Electric Field
By · CommentsEarth will exert a gravitational force on any object that approaches it. Let’s say an asteroid or a meteor or a commit , anything that gets close to earth is going to feel the pull. The earth has a gravitational field. Electric charges exert forces on other electric charges. So electric charges are surrounded by an electric field. This concept was introduced by Michael Faraday.
Electric Field= is a force field that surrounds every electric charge or group of charges.
It is the ratio of the electric force experienced by a small test charge at a point in space to the small test charge itself.
Calculating Electric field
By · CommentsMagnitude of the electric field can be calculated using one of the following equations:
Electric Field Direction
By · CommentsDirection of the electric field is in the direction of the electric force on a small positive test charge.
Electric field line or lines of force provide a map of the electric field in the space surrounding electric charges.
Electric field is a vector quantity so it has direction. In the example below, the point charge is positve( in center). The Test charges on the outside( black squares) are positive as well.
Methods of Charging Objects
By · Comments1. Friction(rubbing): as two objects rub together, the resulting heat energy may cause one object to lose electrons and the other object to gain electrons.
2. Contact: By contact, when you take a neutral object and touch it with a charged object. And when a charged object touches a neutral object their can be a transfer of charge from one to the other. Then the neutral object becomes either positively or negatively charged. Think of it as a healthy person being touched by a sick person and the disease or illness is contagious by touch and you have the transfer of the disease from one person to the other.
Conductors vs. Insulators
By · CommentsInsulators-are poor conductors. They do not allow heat and electricity to flow through them very well.
Insulator examples: Rubber, wood, glass
Conductors- they allow both heat and electricity to flow very well through them.
Conductor examples: Metals (silver)
Air is a poor conductor. That is why they tell you in cold weather to wear layers of clothing so that your body heat gets trapped in between the layers and it doesn’t conduct your body heat away as quickly compared to just a single layer.
Electric Force
By · CommentsElectric Force is the force exerted by one electric charge on another electric charge.
Fundamental Principle of Electrostatics: Like charges repel, opposite charges attract. If you have two positive charges placed near each other, they will push each other away (repel). Two negative charges placed close to each other, will push each other away.
If they are opposite charges, one positive and one negative then they are attracted to each other.
Example:
Law of Conservation of Electric Charge
By · CommentsLaw of Conservation of Electric Charge- During any process, the net electric charge of an isolated system remains constant ( is conserved).
Total charge before= Total charge after.
Within the system.The total charge is always the same, or the total number of Coulombs will always be the same. If there is any exchange or transfer of electric charge between one object and another in the isolated system, then the total number of charge is the same. It’s just like the two conservation laws:
Conservation of Momentum: Where total momentum of an isolated system is the same.
Weight vs. Mass
By · CommentsWeight
The weight of an object on or above the earth is the gravitational force that the earth exerts on the object.
Weight measures gravity between two bodies.
The weight always acts downward, toward the center of the earth
SI unit for weight =Newton ( N)
W=m x g m=mass g=gravity ( 9.8 m/s²)
Weight is the gravitational force acting on the object and can vary depending on how far the object is above the earth’s surface or whether it is located near another body such as the moon.
Gravity becomes smaller as you go farther away from the earth.
First law of motion
By · CommentsAn object remains at rest, like a table, or remains in motion at constant velocity, like your car set on cruise control, unless acted upon by a net force.
Everything that has mass has inertia. You and I have inertia. The books, the book bags, the desk, elephants, cars, planes, cell phones, pencils, you get the idea. Everything that is made of matter has inertia.
Inertia is the natural tendency of anything to resist change in its motion .Or, if it’s at rest it will resist any change in its state of rest.
First Law of Inertia
By · CommentsNewton’s first law of motion is also know as the law of Inertia. An object remains at rest or remains in motion at constant velocity unless acted upon by an unbalanced force. Have you ever seen a magician perform the table cloth trick? This deals with Newton’s first law of motion. Here is an example below:
Physics Practice Test 1
By · Comments1. Which of the following is a vector quantity?
A. speed B. mass C.time D. displacement
2. What would 25 miles/hour be if converted in meters/second?
A. 16.7 m/s B. 46.4 m/s C. 11.2 m/s D. 35.9 m/s
3. If the area of a lake is 15 km ² , then what is the lake’s area expressed in units of m²?
A. 1.64 x10 ^3 m² B. 1.50 x 10 ^2 m² C. 1.50 x 10^4 m² D. 1.50 x 10 ^7 m²
4. The standard SI unit of mass is ?
A. gram B. kilogram C. slug D. newton
Displacement
By · CommentsDisplacement is how far and in what direction an object had moved from its original position.
SI unit: meter (m)
Displacement is a vector quantity because it deals with magnitude and direction. Displacement takes the direction of the motion into account, and distance does not.
Vector Quantity
By · CommentsA vector quantity is a quantity that deals with both magnitude (number and unit) and direction.
Because direction is an important characteristic of vectors , arrows are used to represent them. The direction of the arrow gives the direction of the vector. The length of the arrow is proportional to the magnitude of the vector.
N
W E
S
Example of a vector quantity:
250 m, due east
Scalar Quantity
By · CommentsA scalar quantity is one that can be described with a single number, including any units, giving its size and magnitude.
Examples of scalar quantities:
Volume: 50 meters
Time: 35 seconds
Temperature: 25 ° C
Mass: 90 kg
A scalar quantity is a quantity that is described by its magnitude( number and unit).
Pythagorean Theorem
By · CommentsPythagorean Theorem
c²=a²+b²
Pythagorean Theorem:The square of the length of the hypotenuse of a right triangle is equal to the sum of the squares of the lengths of the other two sides.
Trigonometry Review
By · CommentsTrigonometry=The branch of mathematics dealing with the relations of the sides and angles of triangles and with relevant functions of any angles.
Torques and rotational motion
By · CommentsDownload the MP3 Torque lecture
Torque is the product of force and the distance from the axis of rotation. There must be force applied at some distance from the axis of rotation. Because if the force is applied right at the axis of rotation, then there is no torque, and the object won’t rotate.
Lever arm defined: The distance from the applied force to the axis of rotation. It’s expressed in (m) meters.
SI unit of Torque: Newton meter (N·m)
If the force and lever arm are perpendicular to each other, then theta θ = 90 °. The sin of 90 degrees =1, so the formula is just F x l .
Torque
By · CommentsTorque (τ) =Magnitude of the force x Lever Arm=F x l
Direction: Torque is positive when the force creates a counterclockwise rotation about the axis.
Torque is negative when the force creates a clockwise rotation about the axis.
Torque is represented by greek letter tau (τ)
SI unit of Torque: newton meter (N·m).
Angular Displacement problem
By · CommentsTwo space stations are in orbit above the moon. Their radius 5 x 10^7 meters. The angular displacement( Θ ) of the two space stations is 4 degrees. What is the arc length(s) that seperates them?
Formula needed to solve problem: Θ( in radians)= s
r
Angular Acceleration (α)
By · CommentsRight click to download mp3 angular acceleration
Angular Acceleration(α)=The change in the angular velocity per unit time.
SI unit: rad/s²
(α)=ω final – ω initial=Δω ω=omega
t final – t initial =Δt t=time
Angular Velocity (ω)
By · CommentsRight click to download mp3 angular velocity
Angular Velocity(ω)=Change in the angular displacement(θ) per unit time.
SI unit: rad/s
Sometimes expressed as revolutions/rotations per minute(rpm)
ω=θ final – θinitial=Δ θ *ω=greek letter=omega
t final – t initial =Δ t t=time in seconds
