Physics 2- Exam 2

What is the equivalent resistance when R1, R2, and R3 are all connected in parallel?

(1/R1 + 1/R2+ 1/R3)-1

Which of these is a property of current?

-Causes light bulbs to glow -Deflects compass needles -Causes wires to get warm

Electric fields

-Point from higher to lower potential -Are perpendicular to equipotential lines -Are stronger where the equipotential lines are closer together

The resistance of a wire to current flow depends on

-The cross-sectional area of the wire -The length of the wire -The material of the wire

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

You are given an aluminum bar of dimensions 10 cm x 4 cm x 1 cm and asked to attach leads to it in order to make a resistor. If you want to achieve the smallest possible resistance, you should attach the leads to the opposite faces that measure

10 cm x 4 cm

What is the current in a circuit with a 10 V battery and 1000 ohms of resistance?

10mA

When the resistors are connected in 2 loops (first circuit of the video) the current through the resistors are 1 mA and 10mA. What is the current in the circuit before the junction that splits to the 2 resistors?

11 mA

A circuit consists of 1 battery and 2 identical resistors connected in parallel to the battery. The battery has an emf of 12 V. What is the potential difference across the first resistor?

12 V

A circuit consists of 1 battery and 2 identical resistors connected in series with the battery. The battery has an emf of 12 V. What is the potential difference across both resistors?

12 V

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

2.5 V

The equivalent resistance of 2 identical resistors with resistance R, which are connected in series is

2R

Two ideal parallel-plate capacitors are identical in every respect except that one has three times the plate area of the other. If the smaller capacitor has capacitance C, the larger one has capacitance

3C

When a dielectric material is introduced between the plates of a parallel-plate capacitor and completely fills the space, the capacitance increases by a factor of 5. What is the dielectric constant of the material that was introduced?

5

What is an electric dipole?

A neutral object with a separation between positive and negative charges

The electron volt is

A unit of energy

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) The resistance of wire #1 is twice as high as that of wire #2.

Several capacitors are connected in series with a battery. The potential difference across each capacitor

Adds to equal the emf of the battery

Which sequence describes how current is created?

An electric potential creates an electric field which creates the current

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

An escalator

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) Their kinetic energy keeps increasing. C) Their electric potential energy keeps decreasing. E) Their acceleration keeps decreasing.

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.

B) sphere #1 carries positive charge and #2 carries negative charge.

Consider two gold wires of equal cross-sectional area. One wire is 4 times as long as the other. How do the resistivities of the two wires compare?

Both wires have the same resistivity

How are electric forces between several charged objects combined?

By adding the individual vectors.

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) Both the charge on the plates of the capacitor and its capacitance would change.

The unit of capacitance, farad, F, is equal to

C/V

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

C/s

What is the equivalent capacitance for capacitors C1, C2, and C3 when they are connected in parallel?

C1+C2+C3

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 does the law of conservation of charge mean?

Charge is neither created nor destroyed when it is transferred.

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

Chemical energy

Materials in which charges move easily are known as

Conductors

Electric fields are

Created by charged objects altering the space around them

A parallel plate capacitor

Creates a uniform electric field between two oppositely charged plates

Kirchhoff's junction law states that

Current into a junction is equal to current leaving it

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

Current is the flow of positive charge

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) 4C

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) It is 1/2 as large.

In outer space, a positive charge q is released near a positive fixed charge Q, as shown in the figure. Asq 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) It will move with decreasing acceleration. E) It will move with increasing speed.

X and Y are two initially uncharged metal spheres on insulating stands, and they are in contact with each other. A positively charged rod R is brought close to X as shown in part (a) of the figure. Sphere Y is now moved away from X, as shown in part (b). What are the final charge states of X and Y? A) Both X and Y are neutral. B) X is positive and Y is neutral. C) X is neutral and Y is positive. D) X is negative and Y is positive. E) Both X and Y are negative.

D) X is negative and Y is positive.

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) introduce a dielectric material between the plates E) decrease the separation between the plates

An electron is initially moving to the right when it enters a uniform electric field directed upwards, as shown in the figure. Which trajectory (X, Y, Z, or W) will the electron follow in the field? A) trajectory W B) trajectory X C) trajectory Y D) trajectory Z

D) trajectory Z

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) v0√2

The electric potential in a charged parallel plate capacitor

Decreases from the positive plate to the negative plate

A parallel plate capacitor has horizontal plates. The top plate has a positive charge and the bottom plates has a negative charge. What is the direction of the electric field in the capacitor?

Down

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) It remains the same.

Which of the following is a real physics field?

Electric Gravitational Magnetic

What are the charge carriers in a metal?

Electrons

What is the force on a charge Q in an electric field with strength E?

F = QE

How can charge be moved?

Friction Contact Polarization

The electrical potential at a resistor is

Higher at the end the current enters

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

To measure the potential difference at a circuit element a voltmeter must be connected

In parallel with the element to be tested

To measure current in a circuit the ammeter must be connected

In series with the circuit elements

Where is the energy stored in a capacitor?

In the electric field

What change would decrease the resistance of a wire?

Increase the cross-sectional area

The electric potential energy of 2 charged objects with the same sign charge

Increases as they are moved closer together

The capacitance of a capacitor can be increased by

Inserting an insulator between the plates

The force between an electron and proton

Is attractive

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

Is perpendicular to the surface of the conductor

The energy stored in a capacitor

Is proportional to the potential difference squared

Several capacitors are connected in series with a battery. The charge on the capacitors

Is the same for each capacitor

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 two charged objects what happens to the force between them?

It increases

The length of a certain wire is doubled while its radius is kept constant. What is the new resistance of this wire?

It is 2 times as large

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

Its charge

The electric field due to a point charge q is

K(q/r2)

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

Large charge transfer

The resistivity of a good conductor is

Lower than insulators

What type of charge can move within a conductor?

Negative

When do electric field lines cross?

Never

How are car headlights connected?

Parallel

Electric field vectors

Point toward negative charges and away from positive charges

Video 1: What is the sign of the charge on the sticky side of the tape after he sticks 2 pieces of tape together and then pulls them apart?

Positive

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 a complete circuit

A battery supplies which 2 things?

Potential difference and energy

A lightning rod is intended to

Prevent a lightning strike by ionizing the air around it.

The potential difference between plates of a parallel plate capacitor is

Proportional to the charge on the plates

The equivalent resistance of 2 identical resistors, with resistance R, which are connected in parallel is

R/2

What is the equivalent resistance when R1, R2 and R3 are all connected in series?

R1+R2+R3

Which circuit element has a zigzag for its symbol?

Resistor

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

Same before and after the resistor

Kirchhoff's loop law

Says the potential difference around a loop is zero

A potential difference can be created by

Separating positive and negative charges

The capacitance of a parallel plate capacitor only depends on

The area of the plates and the distance between the plates

Kirchhoff's junction law states

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

In a series circuit with 2 resistors

The current flows through one resistor then the next

In a parallel resistor circuit with 2 resistors

The current splits and flows through both resistors at the same time

A dielectric material such as paper is inserted between the plates of a capacitor as the capacitor holds a fixed charge on its plate. What happens to the electric field between the plates as the dielectric is inserted?

The field becomes weaker

What happens to the electric field in the capacitor as the charge, Q, stored in it increases?

The field increases as Q.

You measure a force between 2 charged objects. What happens to that force if the distance between the objects is reduced to ½ of what it was?

The force is increased a factor of by 4.

Two tiny beads are 25 cm apart with no other charges or fields present. Bead A carries 5 µC of charge and bead B carries 1 µC. Which one of the following statements is true about the magnitudes of the electric forces on these beads?

The force on A is exactly equal to the force on B

A charged object moves freely in an electric field. As its electric potential energy decreases what can be said about its kinetic energy?

The kinetic energy increases

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

The positively charged plate

Each pair of leads used to make an electrocardiogram measure

The potential difference between the leads

A negatively-charged rod is brought close to (but does not touch) two neural spheres that are in contact with each other but insulated from the ground. If the two spheres are then separated, what kind of charge will be on the sphere?

The sphere near the charged rod becomes positive and the other one becomes negative

A solid copper cube rests on a wooden table in a region where a uniform external electric field is directed straight downward. What can we say concerning the charge on the top surface of the cube?

The top surface is charged negatively

two protons are fired toward each other in a particle accelerator with only the electrostatic force acting. Which of the following statements must be true about them as they move closer together?

Their electric potential energy keeps increasing

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 the energy quickly

Which has a larger magnitude charge, proton or electron?

They have the same amount of charge, but opposite signs.

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

They were the same

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

U = K (q1*q2)/r

What direction is the force on an electron due to Earth's electric field?

Up

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

V ∝ 1/r

Another term for the electrical potential difference between 2 points (like a battery) is

Voltage

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=ΔU>0

Electric field lines are closer together

When the electric field in stronger

In the model of an ideal wire in a circuit

Wires have 0 Ω 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.

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

Zero

When a current flows through an ionic liquid such as salty water, the moving charges are

both positive and negative ions

The electron-volt is a unit of

energy

A plastic rod is charged by rubbing with a wool cloth, and brought to an initially neural metallic sphere that is insulated from ground. It is allowed to touch the sphere for a few seconds, and then is separated from the sphere by a small distance. After the rod is separated, the rod

is repelled by the sphere

As a proton moves in the direction the electric field lines

it is moving from high potential to low potential and losing electric potential energy

The electric potential energy of a charge q in terms of the electric potential, V, of the space around it is

qV

The energy stored in a capacitor is equal to

½ C(ΔVC)2 ½ Q2/C ½ Q (ΔVC)

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

ΔV = Q/C