Physics 2 - Final

Charge is moving through a wire. An amount of charge Q moves past a particular spot in the wire in an amount of time t to produce a current of I. (a) What happens to the magnitude of the current when it takes five times as long for the same amount of charge to be moved past that point in the wire at a steady rate? (b)What happens to the magnitude of the current when the amount of time to move the charge does not change, but the amount of charge moved past that point in the wire at a steady rate is four times as much? Ch. 18 Hw7

(a) new current is is I/5 (b) new current is 4I

Four charges of equal magnitude Q but varying sign are placed at the corners of a square. A positive charge q is placed at the center. (a) What is the direction of the net force on the center charge? (b) now suppose that charge q were to be displaced slightly from the center position. One the figure, label each box with the arrow that best indicates the direction of the net force that would act on q if it were moved to that location

(a) no force

In the figure, four point charges lie on the corners of a square, with a 5th point charge q in the center. The two left charges have the same negative charge qn, and the two right charges have the same positive charge qp. Assume the center charge q is negative. (a) What is the direction of the total electric force on the charge q at the center of the square? (b) What is the direction of the electric field at the center of the square, due to the four corner charges?

(a) towards the right (b) towards the left

Examples of conduction

- the burner on an electric stove heating a pot -involves direct contact between surfaces -touching a hot baking dish with your bare hand is an example of this form of heat transfer

A point charge +Q is at the center of a spherical conducting shell of inner radius R1 and out radius R2. The total charge on the inner surface of the shell is... Ch.16

-Q

Examples of radiation ch. 14

-can travel through the vacuum of space -sunlight is an example of this -baby chicken eggs are kept under this

Examples of convenction ch.14

-involves the movement of fluid -heat travels best in gases and liquids using this method of heat transfer -this form of heat transfer occurs in teh interior of the Earth, when the hot magma rises toward the surface

Consider a scenario in which a point charge +Q is located outside a closed surface represented by the dark circle in the figure What is the net electric flux through the closed surface

0

An observer sits in a boat watching wave fronts move past the boat. The distance between successive wave crests is 0.8m and they are moving at 2.2 m/s (a) what is the wavelength of these waves? (b) what is the frequency of these waves? (c) what is the period of these waves? ch.13

0.8 2.8 0.36

The amount of heat Q that is conducted through a material depends on:

1. The time during which conduction takes place. 2.The temperature difference between the ends of the bar. 3.The cross sectional area of the bar. 4.The length of the bar.

Classify each statement according to whether it describes electric force, gravitational force, or neither force 1. acts on charge 2. can be either an attractive or repulsive force 3. can be zero between two objects 4. can only be a repulsive force 5. acts on mass 6. can only be an attractive force 7. can never be zero between two objects

1. electric 2. electric 3. electric 4. neither 5. gravitational 6. gravitational 7. gravitational

Label each statement according to whether it refers to AC, DC, both, or neither 1. The current is always constant in these types of circuits 2. The current in this type of circuit travels in the same direction at all times 3. This type of current is harmless 4. This is the type of current that runs from a far-away power plant to a household 5. the battery in a laptop computer delivers this type of current 6. 22 V at 60 Hz specifies this type of power supply Ch. 18 Hw 7

1. neither 2. DC 3. neither 4. AC 5. DC 6. AC

Two identical speakers are emitting a constant tone that has a wavelength of 0.50 m. Speaker A is located to the left of speaker B. At which of the following locations would complete destructive interference occur?

3.75 m from speaker A and 2.5 m from speaker B

Standing waves are set up on a string that is fixed at both ends so that ends are nodes. How many nodes are there in the fourth mode, including the endpoints?

5

When a wire that has a large diameter and length L is connected across the terminals of a battery, the current is 40 A. If we cut the wire to half of its original length and connect one piece that has a length L/2 across the terminals of the same battery, the current will be___ Ch 18 Hw 7

80 A

An ideal gas is enclosed within a container by a moveable piston. If the final temperature is two times the initial temperature and the volume is reduced to one -fourth of its initial value, what will the final pressure of the gas be relative to its initial pressure, P1?

8P1

Three identical conducting spheres on individual insulating stands are initially electrically neutral. The three spheres are arranged so that they are in a line and touching as shown. A negatively-charged conducting rod is brought into contact with sphere A. Subsequently, someone takes sphere C away. Then, someone takes sphere B away. Finally, the rod is taken away. What is the sign of the final charge, if any, of the three spheres? ch. 16 2/12

A - B - C -

In each of the scenarios, two spheres of the same size and shape hang from an attachment point. Each sphere is electrically charged and is either perfectly conductive or perfectly insulating, as indicated in the key. The magnitude of charge Q is greater than the magnitude of charge q. Each pair of spheres is allowed to swing freely and comes to rest in some equilibrium position. In each scenario, determine whether the spheres come to rest in contact, or separated by some distance. Assume that the weight of the spheres is small enough that electrostatic forces are significant.

Black = conductive Orange = insulating

The electric field E and the potential V at the center of the square are

E not equal to 0 V = 0

How many electrons are in one coulomb of negative charge? ch. 16 2/12

N = q/e = 6.25x10^18

unit for B

N/m²

PV = nRT versus PV = NkT

PV = nRT is first gas law where n is total number of moles of gas PV = NkT is second gas law where N is total number of gas molecules

Why does a can of compressed air or a fire extinguisher get cold when you spray it?

Pressure decreases so the temperature decreases

constructive interference

The interference that occurs when two waves combine to make a wave with a larger amplitude

destructive interference

The interference that occurs when two waves combine to make a wave with a smaller amplitude

Metal pots used in cooking on top of a stove are usually very shiny on the top and sides. Which one of the following choices indicates why this is a good idea thermally?

The shiny parts of the pot have greatly reduced losses via radiation

constructive interference

When two waves always meet condensation to condensation and rarefaction to rarefaction, they are said to be exactly in phase and exhibit constructive interference

A heater element becomes warm when an electrical current is passed through its wires. The more current that passes through, the hotter the wires become. When looking at the wires they are glowing orange; and if you are standing in front of this heater, you will feel the warmth of it. While standing in front of this heater, someone else covers it with a glass jar and then removes the air from the jar using a vacuum pump. Can you still feel the warmth of the heater? ch. 14 2/10

Yes, you will still feel warm because heat is transferred via electromagnetic waves that can travel through the vacuum

Surface waves

a combination of transverse and longitudinal waves example: waves on a body of water

Sinusoidal waves

a wave in the shape of a sine or cosine curve

A free positive charge released in an electric field will

accelerate in the direction in which the electric field is pointing

A free negative charge released in an electric field will

accelerate in the direction opposite the electric field

Electric charges of the opposite sign ____ each other

attract

Explain why capacitance C depends neither on the stored charge q nor on the potential difference V between the plates of a capacitor

capacitance is determined only by the physical properties of the capacitor

The doppler effect ch. 13 2/5

change in frequency or pitch of the sound detected by an observer because the sound source and the observer have different velocities with respect to the medium of sound propagation -example: hearing siren sound fade out as it passes you while you are standing

Two point sources produce waves of the same wavelength that are in phase. At a point midway between the sources, what kind of interference would be observed?

constructive interference

Consider the following substances all at room temperature: (1) aluminum: 240 J/(s·m·°C) , (2) copper: 390 J/(s·m·°C), and (3) wood: 0.15 J/(s·m· °C). Which one would feel the coolest if held in your hand? Note: Your hand is at a temperature above room temperature.

copper

An isolated parallel plate capacitor carries a charge Q. If the separation between the plates is doubled, the electrical energy stored in the capacitor will be ________ Ch 17 Hw 6

doubled

Consider the figure with a symmetrical arrangement, in which qa = qb = +7.85uC, qc = qd = -7.85 uC, and q is positive Using the symmetry of the arrangement, determine the direction of the force on charge q

down

Law of conservation of electric charge ch. 16 2/12

during any process, the net electric charge of an isolated system remains constant (is conserved)

The sound you hear coming from a speaker is higher pitched than expected. What might cause this?

either you are moving towards the speaker or the speaker is moving towards you

Substances that readily conduct electric charge are called ________

electrical conductors

Materials that conduct electric charge poorly are called ____________

electrical insulators

The electric potential, when measured at a point equidistant from two particles that have charges equal in magnitude but of opposite sign, is ch 17 hw 6

equal to zero

If a negative charge is released in a uniform electric field, it will move...

from low potential to high potential

A capacitor consists of a set of two parallel plates of area A separated by distance d. This capacitor is connected to a battery that maintains a constant potential difference V across the plates. If the separation between the plates is doubled, the electrical energy stored in the capacitor will be ______ Ch 17 hw 6

halved

If the thickness of a uniform wall is doubled, the rate of heat transfer through the wall is ch. 14

halved

Convection

heat is carried from one place to another by the bulk movement of fluid examples: boiling water on stove has convention current, hot water baseboard heating units make convection currents in the home, refrigerators have cooling coils that create convection forced convection is used in fan engines

Conduction

heat is transferred directly through a material -occurs when the atoms or molecules in a hotter part of the material vibrate or move with greater energy than those in a cooler part -through collisions, the more energetic molecules pass on some of their energy to their less energetic neighbors

Sound waves transmit faster in ________ temperatures versus ________ temperatures

higher, lower

Gauss's Law indicates that the flux through a closed surface ch 16

is proportional to the net charge enclosed

For a positive charge moving in the direction of the electric field....

its potential energy decreases and its electric potential decreases

thermal conductors

materials that conduct heat

thermal insulators

materials that conduct heat poorly

amplitude

max displacement from y=0

Longitudinal waves

medium oscillates along the direction of propagation of the wave example: compression of a spring and sound waves

Transverse wave

medium oscillates perpendicular to the direction the wave travels example: wave on a string

When a glass rod is rubbed with silk cloth, the rod becomes positively charged as ... ch. 16 2/12

negative charges are transferred from the rod to the silk

Can an object carry a charge of 2.4x10^-19 C?

no because charge is quantized

An equipotential surface must be ___________

perpendicular to the electric field at every point

A positively charged rod is brought near one end of an uncharged metal bar. The end of the metal bar farthest from the charged rod will be charged...

positively

A proton and electron are fixed in space with a separation of 993 nm. Calculate the electric potential at the midpoint between the two particles. Find magnitude of electric field at same point. The direction of the field is _____ ch. 17 Hw6

potential: 0 V1 = kqe/r1 V2 = kqe/r2 V1 + V2 = 0 (cancel out) magnitude of field: 11683 E+ = k|q1|/r^2 E- = k|q2|/r^2 E+ + E- = magnitude of E direction: to the right

Why do beer bubbles grow in size as they move upward in a glass?

pressure decreases as the bubble moves upward and the volume increases as a result

Radiation

process in which energy is transferred by means of electromagnetic waves. no contact is required -a material that is a good absorber is also a good emitter -material that absorbs completely is called a perfect blackbody

In a tube open at both ends:

sound waves reflect from both ends of the tubes

How is it possible to transfer electric charge from one object to another?

the body that loses electrons has an excess of positive charge, while the body that gains electrons has an excess of negative charge

wavelength

the distance from any point on a wave to an identical point on the next wave

Why is the gravitational force usually ignored in problems involving particles such as electrons and protons?

the electric force between charged particles is much greater than the gravitational force

A trombone has a variable length. When a musician blows into the mouthpiece and causes air in the tube of the horn to vibrate, the waves set up by the vibrations reflect back and forth in the horn to create standing waves. As the length of horn is made shorter, what happens to the frequency?

the frequency increases

Coulomb's Law

the magnitude of the electrostatic force exerted by one point charge on another point charge is directly proportional to the magnitude of the charges and inversely proportional to the square of the distance between them

Explain how a light material, such as fiberglass insulation makes an effective barrier to keep a home warm in the winter and cool in the summer

the material traps air between the fibers. This reduces the amount of heat transfer between a home and the outside because air has a low thermal conductivity. In addition, the air is trapped in small pockets which prevents convection further reducing heat transfer

Electric flux is proportional to

the number of electric field lines passing through a surface in a field line diagram -field lines passing into the surface are considered negative, field lines passing out through the surface are positive

Positively charged particle trajectories can but do not have to follow electric lines because

the particle velocities may or may not be in the same direction as the electric field lines

Pitch increases when

the source moves closer to the listener or the listener moves closer to the source

The antinode is where __________

there are no vibration of air molecules

You venture out on a cold winter morning to warm up your vehicle. You have layers of cotton/polyester blend clothes on, and from walking on carpeting, you have accumulated a net negative charge. Your car is considered a neutral conductor As you place your hand near the door handle (without touching it), what happens to the charges of your car?

there is a localization of positive charge near the door handle

Electric charge can exists on an object and move __________ and object

through

You are walking along a small country road one foggy morning and come to an intersection. While you are crossing, you hear an ambulance siren. As a paramedic, you know that the siren sounds at frequency of 9.07 kHz. But as an amateur musician with perfect pitch, you can tell that the frequency you are hearing is actually 9.75 kHz. Is the ambulance moving toward or away from you? ch. 13

toward

Sounds coming from moving objects, such as the siren of an emergency vehicle, appear to change pitch as the object moves toward or away from an observer. Compare the frequency of a siren based on its speed and direction of motion. Highest to lowest

toward you at 49 mph > toward you at 36 mph > toward you at 7 mph > neither toward nor away from you > away from you 21 mph > away from you at 36 mph

Materials with __________ are usually excellent thermal insulators because they can create very small convection currents

trapped air spaces

Consider the symmetrically arranged charged in the figure, in which qa = qb = -3.45 uC and qc = qd = +3.45 uC Determine the direction of the electric field at the location of charge q

up

During the summer, sunlight warms the land beside a cool lake. This warming is followed by a breeze blowing from the direction of the lake toward the land. Which of the following provides the best explanation for this summer breeze?

warm air rises from above the land and is replaced by the air blowing in from the lake

Sound travels faster in ______ than in _______

water, air

Mechanical wave

wave caused by motion of a medium

Why do we use double paned windows instead of a solid glass window? ch 14 2/10

we use double paned windows because they have air in between them and air is less conductive than glass, so keeps it from effecting temperature in the house better

Principle of linear superimposition

when two or more waves are present simultaneously at the same place, the resultant disturbance is the sum of the disturbances from the individual waves

destructive interference

when two waves always meet condensation to rarefaction, they are said to be exactly out of phase and exhibit destructive interference

A positive charge is moved from one point to another point along an equipotential surface The work required to move the charge is _______ Ch. 17 Hw6

zero

If a charge is located at the center of a spherical volume and the electric flux through the surface of the sphere is Φ, what would be the flux through the surface if the radius of the sphere were tripled? ch. 16

Φ

A transverse standing wave is present on a plucked guitar string. What is the distance from a fixed end of a string to the nearest antinode? ch. 13 2/3

λ/4

B =

ρv²