ELECTRICITY!
Units
Charge - q (Coulomb)
Voltage - V or J/c (volt or joules per charge)
Current (I) - A
Power - W (watts)
Resistance - Ω (ohm)
In electricity, there has to be a complete circuit. There must be a negative and positive end.
Electric Fences
When you touch an electric fence, the shock goes through your body, into the ground, and then back up to the fence, in a circuit.
However, when you stand on a tile, the shock cannot get through you into the ground, therefore, you cannot get shocked, because it cannot go in a circuit.
How does energy go through a wire?
when light switch is turned on, energy is pushed forward and wires are connected, the charges are pushed into the bulb...light! When it is turned off, the wires are disconnected.
CURRENT ALWAYS FLOWS THROUGH THE PATH OF LEAST RESISTANCE
CHARGES
positive charges=protons
negative charges=electrons
neutral charge=when protons and electrons are even
like charges repel each other
opposite charges attract eachother
Polarization
conductors vs. insulators
Conductors: charges can move through them, can become polarized
Insulators: stops charges from moving
*polarization*--Is when charges in an object completely separate. charges move to opposite sides and the object as a whole becomes neutral.
(he wears polarized ray ban sunglasses.)
Colomb's Law
The force between 2 charges is inversely proportional to distance.
F=K(q1q2/d^2)
Big question....polarization question!
Why does a charged piece of cling wrap attract to a ceramic bowl?
when the charged cling wrap gets close to the bowl, the bowl polarizes. Positive charges go towards the cling wrap and negative charges repel away from it. The bowl is polarized therefore has a neutral charge. Since the distance between the opposite attractive charges is less than the distance between the repelling charges, the attractive force is greater than the repelling force. (Colomb's law)-F=K(q1q2/d^2) So....because the attractive force is greater, the cling wrap is attracted to the ceramic bowl.
Polarization
conductors vs. insulators
Conductors: charges can move through them, can become polarized
Insulators: stops charges from moving
*polarization*--Is when charges in an object completely separate. charges move to opposite sides and the object as a whole becomes neutral.
(he wears polarized ray ban sunglasses.) Colomb's Law
The force between 2 charges is inversely proportional to distance.
F=K(q1q2/d^2)
Big question....polarization question!
Why does a charged piece of cling wrap attract to a ceramic bowl?
when the charged cling wrap gets close to the bowl, the bowl polarizes. Positive charges go towards the cling wrap and negative charges repel away from it. The bowl is polarized therefore has a neutral charge. Since the distance between the opposite attractive charges is less than the distance between the repelling charges, the attractive force is greater than the repelling force. (Colomb's law)-F=K(q1q2/d^2) So....because the attractive force is greater, the cling wrap is attracted to the ceramic bowl.
Big question....(sorry I know its scary, but this is the best picture I could find)
Why does your hair stand up after you put on a sweater?
Sweater rubs against hair and steals electrons through friction. Sweater becomes negatively charged and hair becomes positively charged. So hair sticks up because it is attracted to the negative sweater as you put it over your head. Additionally, it repels itself because it is all positively charged.
3 major ways to charge something
1) Contact: transfers charges
2) Friction: when something rubs up they can steal electrons
3) Induction: charge without contact
Induction in more detail:
Induction is caused by putting a positive object next to something without actually touching it. It is all about electrical force, force between different charges.
Electrostatics: Charges that are not moving
Circuits: not a part of electrostatics
Lighting
How does lightning work?
Clouds are charged by energy from air currents. This causes the bottom of clouds to become negatively charged. These negative charges create a charge separation in the earth. (positive is attracted upward, negative repelled downward). The negative charges in the cloud bottoms and the positive charges in the ground build up, eventually the charges equalize across the air, releasing energy in the form of light heat and sound....Lightning!
Lightning rods?
Lightning rods protect buildings from lightning...but how? First, they collect positive charges from the ground and the travel up then stand above the building in the open air. Lightning will take the path of least resistance. The lightning rod will provide far less resistance than the house. Therefore, the lightning will hit the lightning rod rather than the house; thus, protecting the house.
ELECTRIC FIELDS AND SHIELDING
Electric field: an area around a charge that can influence (push or pull) another charge
for positive charges, arrows face outward. For negative charges, arrows face inward.
**if the arrows are closer together, that means the electrical field is stronger**
ELECTRIC SHIELDING
Why do we keep electronics in metal boxes?
The metals charges are all evenly distributed. Therefore, while positive charges accumulate around the box, the objects inside will not feel anything at all. The metal stops them from doing so, and they will not feel a force.
VOLTAGE
voltage=charge difference, the difference in potential energy between two points
bigger charge=bigger voltage=bigger force=higher energy
V=change in PE/q
CURRENT
Current=the flow of charge
VOLTAGE CAUSES CURRENT
2 types of current
AC=alternating current
-switches directions
-used in batteries
DC=direct current
-does not switch directions
-used in wall sockets
How do batteries work?
Batteries have a voltage (or electrical potential difference), therefore have a current. This is because there is a negative a positive side of a battery. This allows a battery to function. However, overtime the difference decreases which means there is no voltage which means no current, so it stops working.
Why do flashlights get dimmer?
This is practically the same question. As the battery gets weaker over time, the voltage therefore current decreases. This means less charge flowing through the bulb and less energy getting transformed into light. So....the light gets dimmer.
ELECTRIC POTENTIAL
charged objects have electric potentials through their location in an electric field.
EP=PE/q
gaining electric potential does not mean gaining kinetic energy
Flashing lights
Cameras use capacitators to use their flash. Capacitators build up energy over a period of time and release all at once. Because of this, photographers cannot back to back take flash photography because the flash needs time to rebuild energy.
**quick side note. Electrons are NOT as fast as light, in conductors they are relatively slow. they move in a pack like formation**
OHM'S LAW
Current depends on voltage and electrical resistance.
V= I x R
Resistance
Resistance is effected by a couple aspects of a wire
-Thicker wire=more resistance
-Longer wire=more resistance
-Heat=more resistance
Why do lightbulbs sometimes blow when you first turn them on?
When a lightbulb is turned off, the filament is cooled, which means very little resistance. When it is turned on, a lot of currents is rushed into the lightbulb without much resistance causing it to sometimes blow.
ELECTRIC POWER
EP=energy/time
EP=V x I
SERIES AND PARALLEL CIRCUITS
circuit=the path in which electrons can flow
Series circuit
-voltage adds
-current decreases
-resistance adds
-one light bulb out, all light bulbs out...this happens when the fuse melts when the current reaches a point that is too great the fuse melts therefore cutting the circuit so everything goes out because they are no longer attached to voltage source.
Parallel circuit
-voltage stays the same
-current adds
-brightness stays the same
-resistance decreases by half
