physics test 3

"In the drawing for question 23, which point, B or C, will have the higher electric potential, assuming the potential is zero at infinity (Hint: Recall that a positive test charge will always move towards a lower potential.)? Explain."

" Point B. Recall that a positive charge will move towards regions of lower electric potential, decreasing its potential energy while gaining kinetic energy, much like a falling rock. Since there is a negative charge at point C a positive charge placed near point C would move toward point C (and if placed near point B would move away from the positive charge at point B), indicating that point C will have a lower electric potential."

"If two charges are both doubled in magnitude without changing the distance between them, will the force that one charge exerts on the other also be doubled? Explain."

" The force between the two charges will be quadrupled. The electrostatic force between the charges varies as the product of the two charges. Doubling each gives a four-fold increase."

"When a glass rod is rubbed by a nylon cloth, which of these two objects gains electrons? Explain."

"The cloth gains electrons transferred from the glass rod. The glass rod becomes positively charged in the rubbing process by losing negatively charged electrons"

"A 47 Ω resistor in a circuit has a voltage difference of 8 V across its leads. What is the current through this resistor?"

.170 amps (8V/47ohms) = amps

1 amp is equal to

1 coulomb per second

" Two identical steel balls mounted on wooden posts initially have different amounts of charge: one −6 μC and the other +28 μC. The balls are allowed to touch and then are separated again. What is the final charge on each ball?"

11. because the formula for q is (q1 + q2)/2

voltage in a wall outlet

119 volts. on average - always changing

"A uniform electric field is directed upward and has a magnitude of 30 N/C. What are the magnitude and direction of the force on a charge of −6 C placed in this field?"

180N down. The -6 changes the y direction to opposite it was to begin with. (-6)(30)(y)

When two small, charged objects are 1 micrometer apart, the magnitude of the electrostatic force each exerts on the other is 4 N. What will be the magnitude of the force each charge exerts on the other when the charges are 2 micrometers apart?

1N - 1/4th the original

If you connected a lightbulb with a resistance equal to 60 ohms to an outlet with a voltage equal to 120 volts, what would be the current in the circuit?

2 amps

"A current of 0.522 A flows through a resistor with a voltage difference of 115 V across it. What is the resistance of this resistor?"

220Ohms Ohms = V/amps

if a distance changes by 2x the force changes by

4x

" A charge of +0.18 C is moved from a position where the electric potential is 20 V to a position where the electric potential is 50 V. What is the change in potential energy of the charge associated with this change in position?"

5.4J. change in PE = (.18C)(50-20V)

What is the frequency of AC electricity in the United States?

60 hz

"Two charged particles exert an electrostatic force of 32 N on each other. What will the magnitude of the force be if the distance between the two particles is increased to twice the original distance?"

8N. because the force doubled and would be 1/4th the original

Current in a batter is ________ current in wall outlets is _________

Direct current, alternating current

electric potential energy

Energy a charge has due to its location in an electric field

Generators and transformers are applications of which law of physics?

Faradays law

Magnetic field lines go out of _____end and into _____ end

N, S

Magnets have a north pole and a south pole. Have scientists ever observed or produced in a lab a magnetic monopole: just a north pole or a south pole alone?

No

If you add a resistor in parallel to an existing resistor, what happens to the total resistance in the circuit?

Reff= 1/R1 + 1/R2

Effects of electric charge

Rubbing different materials together sometimes causes electric charge to move from one material to the other. This charge then produces attractive or repulsive electrostatic forces between objects. Like charges repel one another, and unlike charges attract one another. An electroscope consistently gauges the sign and strength of charge present. Using Benjamin Franklin's labels, there are two types of charge: positive and negative. The positive and negative labels originally meant a surplus or shortage of an invisible fluid in Franklin's model, but we now know that negatively charged electrons are transferred during rubbing.

The red N end of a magnet is trying to line up with the ____- end of earths magnetic field

S

You have two household appliances, both designed to be connected to a 120-volt wall outlet: a food processor with a power rating equal to 500 watts and a coffee maker with a power rating equal to 1,000 watts. How does the current required by the coffee maker compare to the current required by the food processor?

The current required by the coffee maker is __twice______ the current required by the food processor.

what force keeps atoms together

attractive

Electric field lines point [x] positive charges and [y] negative charges.

away from, towards neg

electric field force is stronger when field lines are

closer together

The ______ is the standard unit of electric charge.

coulomb

if resistance is half

current doubles

in a series circuit

current stays the same, voltage changes

If you connect more and more resistors in a series circuit the total circuit current

decreases

As more and more resistors are added in parallel to a circuit, the equivalent resistance of the circuit ________ and the total current of the circuit

decreases, increases

in parallel if resistance is half the current

doubles

doubling volts

doubles current

what makes a magnetic field?

earth, current carrying wire, current loop, permanent magnet

coulombs law

electric force between charged objects depends on the distance between the objects and the magnitude of the charges.

An _______ is a simple device with metal foil leaves that can be used to measure charge.

electroscope

". The force exerted by one stationary charge on another is called

electrostatic force

in a series brightness/current is

equal throughout

If one wire has a current of 12 amps and the other has a current of 8 amps. The force exerted on the let hand wire is _____ the magnitude of the force on the right hand wire

equal to

Two charged objects exert electrostatic forces on one another. Object A is charged +Q and object B is charged +2Q (twice A). The magnitude of the force Object A exerts on Object B is ______ the magnitude of the force Object B exerts on Object A.

equal to

Ideally, the resistance of an ammeter should be very high - true or false

false

magnetic field is tangent to

flow lines

The electric field relates to [x] and the electric potential relates to [y].

force, energy

If you first charge an electroscope negatively, then bring a positively-charged object near the electroscope's top ball, the leaves will

get closer together

what would make magnetic field force weaker?

greater distance

charge flows from

high potential to low potential

If you add a resistor in series to an existing resistor, what happens to the total resistance in the circuit?

higher resistance. Reff=R1+R2

Right hand rule for current loop

if grab the loop the way the current is going thumb says what way the magnetic field is going

If you connect more and more resistors in a parallel circuit the total circuit current

increases

electric potential

measured in volts. mapping

what would make magnetic field force greater?

more current

in parallel if one light bulb goes out

no other ones go out

if current is opposite direction to magnetic field the force would be

none

if 12v moor and 1.5 amos - what is power rating?

p=vi p=(12V)(1.5amps) = 18 watts

electric field lines

point in the direction of the electric field vector (away from positive, and towards negative)

The process by which a neutral insulator is attracted to a nearby charged body, shown in Figure 12.9 of the textbook, is called

polarization

a conventional current flows from

positive to negative terminals

Two parallel wires carry currents in opposite directions. The wires

repel each other

A loop of wire rests on a horizontal table. The loop is connected to a power supply that drives a current which circulates clockwise as you look down on the table. What is the direction of the magnetic field at the center of the loop?

right - thumb says what way its going

When using meters to analyze a circuit, you must connect an ammeter in [x] with the circuit and a voltmeter in [y] with the circuit.

series, parallel

"Why do sparks fly when we shuffle across a carpet on a dry day and then touch a light switch?"

shuffling of feet creates a separation of charge, which then spreads to rest of body. Touching light switch lets the charge discharge bc switch is grounded

The north magnetic pole of Earth's magnetic field is near Earth's ________ geographic pole.

south

if battery only makes 2 volts but need 12v what do you do?

stack 6 batteries. Parallel - makes 2v battery with more current. MORE CURRENT series - 12v battery but not much current MORE VOLTs

a negatively charged objecthas a _____ of electrons while a positively charged object has a ________

surplus, shortage

circuit

the complete path that an electric current travels along

Current in a piece of copper wire is

the flow of electrons from low potential to high potential

in a series if one lightbulb goes out

they all go out

how to find v of voltmeter

v=IR

ohms law

v=IR or I=v/r

The ______ is the standard unit for electric potential.

volt

In a parallel circuit

voltage stays the same, current changes

The magnetic force exerted on a positive charge that is not moving is

zero