# Physics 101 Test 4

version from 2015-11-16 18:39

## Section

T or F. Electricity and magnetism ARE NOT LINKEDF, they are directly related
T or F. gravity is the weakest forceTrue
How do you charge an insulator? How do you discharge an insulator?- By rubbing together different types of materials. - By touching the charged part of the insulator with a conductor
T or F. The charge of an insulator can be discharged anywhere on the objectFalse, the magnetic charge in an insulator is only in the region that was charged
Conductor - Definematerial that can transfer a charge
Insulator - definematerial that CANNOT transfer a charge
Why do you need to insulate a conductor in order to charge it?If a conductor is not insulated it will transfer any charge that you place within it.
Two balloons are charged by rubbing them with a wool cloth, balloon 1 and balloon 2 will stick to a NON-charged surface, why? These same balloons will repel one-another, why? The balloons are charged in the SAME way so they both carry a charged that will attract objects of the opposite charge - Since the balloons were charged by the same material (wool sheet) they will have the SAME charge and repel one-another.
When you charge an object by rubbing it with a wool cloth, the cloth will have the _ charge as the objectOpposite
Conservation of charge - DefineIn an isolated system, the total charge is conserved
Attraction is MORE common than repulsion, why?Because charged objects can attract uncharged objects
What is the induced separation of charges?A charged object moving close to an uncharged metal object, as the charged object gets closer to the uncharged one, the charges within the metal object arrange so that the opposing sides attract
The interaction between any neutral and charged object is ALWAYS _Attraction
When an electroscope is touched with an electroscope it has _ chargesame
Inverse square relationship - DefineThe attractive forces between two objects decreases by the inverse square of their distance. The opposite is true when they get closer together
Coulombs law equationF = K[(q1q2)/(r^2)]
q's in Coulombs lawI Charge I
k in Coulombs law9x10^9 (N*m^2/C^2)
Unit of chargeCoulomb (C)
How can a room made of conducting materials shield a region from all external electrical forces?As long as the amount of electrons present in a material are AT LEAST equal to any incoming electrical forces, the room will be free of any additional electrical forces. Any forces in excess of that materials capacity will lead to a higher overall charge. (Compare to a cup)
Why is anti-gravity not possible?Unlike magnetism which has a - and + force, gravity only has one force, attraction
Electrical force is proportional to an objects _ and NOT its _charge - mass
Explain how an Electric Field worksAn objects charge creates a force of attraction or repulsion based on the size and type of that charge and other objects interact with this field.
Define Electrical fieldA field present at every point in space; the force exerted on a unit + charge placed at the center
Electrical field equation - unitsE = Force/charge - N/C
What are electric field linesLines showing the vector path of the forces and their respective paths
In an electrical field line drawing of two spheres the lines from one go out in all directions and the lines from the other ALL seam to go towards the first, what can you say about the magnetic force of the first?the First sphere's force is at least twice as strong as the the second
T or F.The free electrons on a piece of metal will spread out in all directions in a uniform densityTrue
Electric Field line originate on the _ charged object and end on the _ charged objectPositive - negative
_ is required to move a charged particle in an electrical fieldWork
Electrical potential energy is equal to _- The amount of work done to move an object from its original location (zero location) to where the attracting body is.
In physical problems, only the _ in _ of the EPE mattersDifference - energy
In the Volt equation it does not matter which charged particle we divide by, why?The qty either way is numerically equal to the work required to bring a + test charge of 1 C from 0 reference to the specified fie pt.
Electrical potential energy unitVolt (V)
What is a spark? What condition has to be present?High electrical field where electrons move over relatively small distances. In air, the electrons are drawn towards the + magnetic force and as the e- are accelerating faster and faster they hit other molecules releasing their e- as well. this "cascade" or, high density of e- in one place, is seen as a spark - Dry air
How do objects become charged or discharged?Transferring e-
T or F. Uncharged objects have NO internal chargesFalse, they have an equal number of + and - charges
What is grounding and why do we do it?Establishing an electrical connection to the earth in order to neutralize an object
When two different types of metals are joined a _ potential _ is producedElectrical - difference
How do you charge a storage battery?plug in + to + and - to - and run the charge BACKWARDS
Current - DefineMeasure of the amt of charge flowing past a given section of a circuit in a unit time
Current equation - unitsI = ΔQ/Δt - C/S Ampere (A)
Voltage - DefineMeasure of the change of electrical potential in a given section of a circuit
Resistance - define - exampleThe lessening of a circuits ability to carry a given current - thin wire VS thick wire
T or F. The thinner the wire, the MORE resistanceTrue.
What are the practical purpose of resistors?generating heat (stoves, hair dryers, heaters) and to control the voltage and current in a circuit (TV signals, radios
Ohms Law Equation - unitsR = V/I - (ohm) Ώ
How fast, on average do e- move through a copper wire? explainmillimeters per second - even though the e- are moving fast, they do not usually move in a straight line. As they collide with other e- next to them the KE is transferred. this is also why wires heat up
Ohms LawThe current through a conductor between two points is directly proportional to the potential difference across the two points.
T or F. A battery with a single wire going from - to + will last longer than a battery with a light bulb attachedFalse. The MORE resistance (in this case a light bulb) will slow the current of the battery and prolong the life of the battery; if you only had that wire it would heat up due to the increased current and lack of resistance.
(Pg 455) Do two light bulbs in a series circuit share the current from a battery like a pizza or like a book?A book because first one uses the current 1st and the next one uses it after wards
T or F. In a parallel circuit, any new wires will create a new path for the electricity and therefor they will create less resistance EVEN IF they have a resistor on them. (create MORE current in in the circuit)True
e- current will flow in the path of _ resistanceLeast
Kirchhoff's Junction RuleThe sum of the currents entering any junction in a circuit MUST equal the sum of the currents leaving that junction (which must add up to 0)
Short Circuit - DefineElectricity not taking a path in favor of a path of less resistance
Kirchhoff's Loop RuleAlong any path from the + to the - terminal of a battery, the voltage drops across the resistive elements must add up to the battery voltage (which must add up to 0)
Explain what a "brow out" isIt is a short circuit in a a power grid when a few power sources are asking for too much electricity at once; everything else gets left out.
IN a series circuit, you _ the voltage and the current remain the _Add - same
In a parallel circuit, you add the _ and the _ remains the sameCurrent - Voltage
The voltage between two point in a circuit is = to ? _ The change in electrical potential between those two points
1 ampere =1C per second
Unit for resistanceohm (Ω)
1 watt is equal to1 joule per second