CP2 Unit 2

what is the electric field inside a conductor with 2nC of net negative charge

0

if a hollow conducting sphere has an excess charge of -10mC, what is the electric field inside the sphere

0 N/C

the unit of electric potential is the volt. what is 1V equal to

1 J/C

wire 2 is twice the length and twice the diameter of wire 1. what is the ratio R2/R1 of their resistances

1/2

the energy stored in a capacitor is equal to

1/2 Q²/c 1/2 Q (∆V) 1/2 C (∆V)²

What is the potential difference between one plate of a parallel plate capacitor and a point halfway between the plates if the full potential difference between the plates is 5 V?

2.5 V

Copper wire #1 has a length L and a radius b. Copper wire #2 has a length 2L and a radius 2b. Which statement about the resistance across the ends of the wires is true? A) The resistance of wire #1 is twice as high as that of wire #2. B) The resistance of wire #1 is equal to that of wire #2. C) The resistance of wire #1 is half that of wire #2. D) The resistance of wire #1 is four times higher than that of wire #2.

A

Which sequence describes how current is created?

An electric potential creates an electric field which creates the current

Two protons are released from rest, with only the electrostatic force acting. Which of the following statements must be true about them as they move apart? (There could be more than one correct choice.) A) Their electric potential energy keeps increasing. B) Their kinetic energy keeps increasing. C) Their electric potential energy keeps decreasing. D) Their kinetic energy keeps decreasing. E) Their acceleration keeps decreasing.

B,C,E

A parallel-plate capacitor consists of a set of two parallel plates of area A separated by a distance d. This capacitor is connected to a battery that maintains a constant potential difference across the plates. A slab of a dielectric material is inserted in the region between the plates and completely fills it. What changes would you observe as the dielectric is inserted? (There could be more than one correct choice.) A) Only the charge on the plates of the capacitor would change. B) Only the capacitance would change. C) Both the charge on the plates of the capacitor and its capacitance would change. D) The potential difference across the plates would increase. E) Nothing would change.

C

the unit of capacitance, F is equal to

C/V

The unit of current is the ampere (amp) which is defined as

C/s

A proton is accelerated from rest through a potential difference V0 and gains a speed v0. If it were accelerated instead through a potential difference of 2V0, what speed would it gain? A) 8v0 B) 4v0 C) 2v0 D) v0^√2

D

An ideal parallel-plate capacitor has a capacitance of C. If the area of the plates is doubled and the distance between the plates is halved, what is the new capacitance? A) C/4 B) C/2 C) 2C D) 4C

D

The length of a certain wire is doubled and at the same time its radius is also doubled. What is the new resistance of this wire? A) It stays the same. B) It is 2 times as large. C) It is 4 times as large. D) It is 1/2 as large. E) It is 1/4 as large.

D

Two uncharged metal spheres, #1 and #2, are mounted on insulating support rods. A third metal sphere, carrying a positive charge, is then placed near #2. Now a copper wire is momentarily connected between #1 and #2 and then removed. Finally, sphere #3 is removed. In this final state A) spheres #1 and #2 are still uncharged. B) sphere #1 carries positive charge and #2 carries negative charge. C) sphere #1 carries negative charge and #2 carries positive charge. D) spheres #1 and #2 both carry positive charge. E) spheres #1 and #2 both carry negative charge.

D

Which of the following changes will increase the capacitance of a parallel-plate capacitor? (There could be more than one correct choice.) A) increase the charge on the plates B) decrease the potential between the plates C) increase the potential between the plates D) introduce a dielectric material between the plates E) decrease the separation between the plates

D, E

In outer space, a positive charge q is released near a positive fixed charge Q, as shown in the figure. As q moves away from Q, what is true about the motion of q? (There may be more than one correct choice.) A) It will move with decreasing speed. B) It will move with constant acceleration. C) It will move with increasing acceleration. D) It will move with decreasing acceleration. E) It will move with increasing speed.

D,E

Two point charges, Q1 and Q2, are separated by a distance R. If the magnitudes of both charges are halved and their separation is also halved, what happens to the electrical force that each charge exerts on the other one? A) It increases by a factor of 16. B) It increases by a factor of 8. C) It increases by a factor of 2. D) It increases by a factor of 4. E) It remains the same.

E

what is the force on a charge in an electric field F=

F=QE

How is the current, I, in a conductor related to the resistance, R, of the conductor and the potential difference across it, ΔV?

I = (ΔV)/R

The electrical potential at a resistor in a circuit

Is higher at the end the current enters

electric field due to charge =

K(q/r²)

a charged object moves freely in an electric field. as its electric potential decreases what can be said about it kinetic energy

KE increases

metal spheres 1 and 2 are touching. both are initially neutral. the charged rod is brought near. the spheres are separated. the charge rod is removed. what are the charges on the spheres

Q1 = - Q2 = +

metal spheres 1 and 2 are touching. both are initially neutral. the charged rod is brought near and then removed. the spheres are separated. what are the charges on the spheres

Q1=0 Q2=0

Kirchhoff's junction law states

The current entering a junction is equal to the current exiting the junction

What is the electric potential energy of 2 charged objects q1 and q2, when they are separated by a distance r?

U=K(q1 x q2)/r

The electric potential, V, of a point charge is related to the distance, r, from that charge as

V α 1/r

What is true about the work, W, done on a book, and the change in gravitational potential energy, ΔU, of a book when you lift it at a constant speed

W=∆U>0

what is an electric dipole

a neutral object with a separation between positive and negative charges

a parallel plate capacitor creates

a uniform electric field between 2 oppositely charged plates

The author's analogy for a battery in a circuit is

an escalator

the force between an electron and proton is

attractive

how are electric forces between several charged objects combined

by adding individual vectors

What is the difference between Coulomb's law for forces between charged objects and Newton's law of gravity?

charge forces can be attractive or repulsive while gravity is only attractive

what is the law of conservation of charge

charge is not created or destroyed when transferred

electric fields are created by

charged objects altering the space around them

What type of energy does a battery use to cause charges to move?

chemical energy

how can charge be moved

contact, polarization, friction

What is the convention for the direction of charge flow in the context of electric current?

current is the flow of + charge

the electric potential in a charged parallel plate capacitor

decreases from + plate to - plate

properties of current include

deflection of compass needles, warmth, light

What are the charge carriers in a metal?

electrons

a glass rod has been charged to +12nC and touches a metal sphere. what kind of charged particle was transferred and in what direction if the rods charge is now +8nC

electrons moved from sphere to rod

the electron volt is a unit of

energy

where is the energy stored in a capacitor

in the electric field

how could you decrease the resistance of a wire

increase the cross sectional area

the electric potential energy of 2 charged objects with the same sign charge ____ as they are moved closer together

increases

the capacitance of a capacitor can be increased by

inserting an insulator between the plates

the electric field of a conductor with +3nC of excess charge

is perpendicular to the surface of the conductor, pointing away from the conductor

the equilibrium position of an electric dipole in an electric field

is with the dipole moment in the same direction as the electric field

the electric potential inside a charged conductor in electrostatic equilibrium

is zero

if you decrease the distance between 2 charged objects what happens to the force between them

it increases

the potential energy of a charged particle in an electric field is proportional to

its charge

a battery is connected to a wire and creates a current in the wire. which of the following changes would increase the current

keeping the wire the same length but making it thicker

what is more dangerous, a large electric potential difference or a large charge transfer

large charge transfer

a positive charge released from rest will move in what direction

lower electric potential

the resistivity of a good conductor is

lower than insulators

the resistance of a wire to current flow depends on

material of wire, length of wire, cross sectional area of wire

conductors:

materials in which charges move easily

what type of charge can move in a conductor

negative

when do electric field lines cross

never

what is the direction of the electric field in a charged parallel plate capacitor

positive to negative

What is needed in order for current to flow?

potential difference and complete circuit

what does a battery supply

potential difference and energy

a lightning rod is intended to

prevent lightning strike by ionizing the air around it

the potential difference between plates of a parallel plate capacitor is

proportional the the charge on the plates

the electric potential energy of a charge q in terms of the electric potential V =

qV

a potential difference can be created by

separating positive and negative charges

Which plate in a charged capacitor has the higher electric potential?

the + plate

which has a larger resistance, a 60W or 100W lightbulb

the 60W

the capacitance of a parallel plate capacitor only depends on

the area of the plates and the distance between the plates

What happens to the current in the Play-doh when the shape is changed so that it is longer and thinner?

the current decreases

In a circuit, how does the current before the resistor compare to the current after the resistor?

the current is the same before and after

electric field lines are closer together when

the electric field is stronger

what happens to the electric field in the capacitor as charge stored in it increases

the field increases

you measure a force between 2 charged objects. what happens to the force if the distance between the objects is reduced to 1/2 of what is was

the force increases by a factor of 4

each pair of leads used to make an electrocardiogram meausre

the potential difference between their leads

the energy stored in a capacitor is proportional to

the potential difference squared

neutral objects have zero net electric charge because

there are equal amounts of positive and negative charge

how are the direction of electric field lines related to equipotential lines

they are perpendicular

capacitors are useful because

they can charge slowly and release energy quickly

When the current passed through 2 identical bulbs connected one after the other, which one was brighter?

they were the same

electric field vectors point

toward negative charges and away from positive

what direction is the force on an electron due to earths electric field

up

another term for the electrical potential difference between 2 points is

voltage

In the model of an ideal wire in a circuit

wires have 0Ω of resistance

does the shape of a charged conductor affect the electric field around it?

yes. the field is stronger where the shape is more pointed

How is the potential difference, ΔV, in a capacitor related to the charge, Q, and the capacitance, C?

∆V=Q/C