Physics 1120 Test 1

Which statements are true for an electron moving in the direction of an electric field?

-Its electric potential energy increases as it goes from high to low potential -Its potential energy increases as its kinetic energy decreases -Its kinetic energy decreases as it moves in the direction of the electric field

When two or more capacitors are connected in series across a potential difference

-the potential difference across the combination is the algebraic sum of the potential differences across the individual capacitors -each capacitor carries the same amount of charge -the equivalent capacitance of the combination is less than the capacitance of any of the capacitors

Good conductors are materials that have a lot of free charges Insulators are materials that lack free charges

....

After a glass rod is rubbed against a silk cloth, the glass rod has a charge of +5 and the silk cloth has a charge of -7. What could the original charges of the glass rod and silk cloth have been?

0,-2

Two point charges attract each other with an electric force of magnitude F. If one charge is reduced to 1/3rd its original value and the distance between the charge is doubled, what is the resulting magnitude of the electric force between them

1/12 F

A metal wire of resistance R is cut into four equal pieces that are then placed together side by side to form a new cable with a length equal to 1/4th the original length. What is the resistance of this new cable

1/16 R

When the separation between two-point charges is doubled, the electric force acting between them changes by a factor of

1/4

Two identical small charged spheres are a certain distance apart, and each one initially experiences ab electrostatic force of magnitude F due to the other. With time, charge gradually leaks off of both sphere. When each of the spheres has lost half of its initial charge, the magnitude of the electrostatic force will be

1/4 F

When two equal but opposite charges q1=-q2 are separated by 1.00 cm, they exert a Coulomb force of magnitude F on each other. If each charge is doubled in magnitude, the force becomes

4F

the electric potential at the electron's location

Increases

In a parallel-plate capacitor, how can the capacitance be decreased?

Increasing the gap between the charged plates

Separating the charges in an object without touching it is called

Induction

A tiny styrofoam ball is suspended on a thread. Tests show it gets attracted to a positively charged rod, and also attracted by a negatively charged rod. What can you can conclude about the tiny styrofoam ball

It has zero net charge

An ohmic metal has a cross-sectional area that gradually becomes smaller from one end of the wire to the other. The current has the same value for each section of the wire, so charge does not accumulate at any one point. How does the resistance change?

It increases

An object with negative charge is placed in a region of space where the electric field is directed vertically upward. What is the direction of the electric force exerted on this charge?

It is down

Which statement best explains why a rubber rod becomes negatively charged when rubbed with fur?

Molecules in the rubber rod have a stronger attraction for electrons than the molecules in the fur

A balloon acquires a positive charge when rubbed on a sweater. As a result, the charge is acquired by the sweater is

Negative

An object is said to be _____ if all positive charges in the object are balanced by a negative charge, leaving no net charge

Neutral

A proton is released fringe rest in a uniform electric field

Next 4 questions

An electron is released from rest in a uniform electric field

Next 4 questions, 1-4

The potential difference across a length of wire is decreased. Which of the following does not decrease as well?

Resistance of the wire

A capacitor stores charge Q at a potential difference (delta V). What happens if the voltage applied to the capacitor by a battery is doubled to 2 delta V?

The capacitance remains the same, and the charge doubles

How does the charge of an electron differ from the charge of a proton? How are they similar?

The charge of an electron is negative, while the charge of a proton is positive. They both have the same magnitude, 1.6x 10^-19 C

Two capacitors, C1 and C2, are connected in series across a source of potential difference. With the potential source still connected, a dielectric is now inserted between the plates of capacitor C1. What happens to the charge on capacitor C2?

The charge on C2 increases

Which of the following is false?

The electric field vector points towards higher potential

A proton and an electron are placard in an electric field. Which undergoes the greater acceleration?

The electron

The potential difference across the ends of a wire is doubled in magnitude. If Ohm's law is obeyed, which one of the following statements concerning resistance of the wire is true?

The resistance is not changed

Which one of the following is the correct statement regarding the resistance?

The resistance of a wire is directly proportional to the length of the wire

The battery powering a lightbulb is disconnected. As the lightbulb's heat dissipates, how will the resistance and current change.

The resistance will decrease and the current will be zero

What happens when a charged insulator is placed near an uncharged metallic object?

They attract each other

A coulomb of charge corresponds to 6.24 x10^18 elementary charges of size e=1.602x10^-19

True

A negative ion is an atom that has gained electrons

True

A region of uniform electric field has parallel electric field lines

True

Coulomb's law states that the magnitude of the force between two charges is inversely proportional to the square of the distance between them

True

Electric field lines point towards negative charges and away from positive charges

True

Electric field strength is largest near the sharp points of a charged conductor

True

Electrostatics is the study of electric charges that are not moving

True

Good conductors are materials that have a lot of free charges

True

Insulators are materials that lack free charges

True

Net charge of a conductor distributes itself throughout the volume of the object

True

Where electric field lines are crowded together, the electric field strength is high

True

Ohm's Law

V=IR

When electric current is flowing in a metal, the electrons are moving

at none of the above speeds

Electrons flow through a circuit in the clockwise direction. The current is traveling

counterclockwise

A cylindrical wire has a radius r and length l. if both r and l are doubled, does the resistance of the wire

decrease

A battery is connected to a resistor. Increasing the resistance of the resistor will

decrease the current in the circuit

the electric potential at the proton's location

decreases

the electron's associated electric potential energy

decreases

the proton's associated electric potential energy

decreases

A metallic coin is given a positive electric charge. Its mass

decreases by an amount too small to measure directly

charge carries in a metal are electrons rather than protons because electrons are

loosely bound

A resistor R is made out of a particular material with resistivity P. The cylindrically shaped resistor has length l and radius r. To get four times as much resistance in your resistor you could

make the radius half as big

If a positively charges plastic rod repels an object, the other object

must have a net positive charge

A charged particle accelerates as it moves from location A to location B. If VA=90V and VB=140V, what is the sign of the charged particle?

negative

The electric field at the surface of a positively charged conductor has a direction characterized by

perpendicular outward and away from the charge

When the distance between two charges is halved, the electrical force between the charges

quadruples

the potential difference across a resistor R, and the current running through it, both two times increased. We know that resistance

remains the same

electron's total energy

remains unchanged

the proton's total energy

remains unchanged

An air-filled parallel-plate capacitor is connected to a battery and allowed to charge up. Now a slab of dielectric material is placed between the plates of the capacitor while the capacitor is still connected to the battery. After this is done, we find that

the charge on the capacitor had increased

Two copper wires of different diameters are joined in series in a circuit. A current flows in the wire combination. When the current flows from the larger-diameter wire into the smaller-diameter wire

the current stays the same

When two or more capacitors are connected in parallel across a potential difference

the potential difference across each capacitor is the same

When you rub a plastic rod with fur, the plastic rod becomes negatively charged and the fur becomes positively charged. As a consequence of rubbing the rod with the fur,

the rod gains electrons and the fur loses electrons

A battery is connected to a resistor. As charge flows, the chemical energy of the battery is dissipated as

thermal energy

2.0 uF and 4.0 uF capacitors in series have equal voltages between their plates

False

A Van de Graaff generator cannot attract neutral objects

False

A positive ion is an atom that has gained protons

False

As current flows through a uniform wire, the wire gets hotter because the electrons stop moving and therefore transform their lost kinetic energy into thermal energy in the wire.

False

Electric field lines point towards positive charges and away from negative charges

False

In a conductor like copper metal, all of its electrons are free to move

False

The electric field inside a conductor carrying a current is zero

False

The electric force on an electrically neutral object is always zero

False

The net charge of a piece of metal is the same as its free charge

False

Two capacitors are identical. They can be connected in series or in parallel. If you want the smallest equivalent capacitance fo the combination, how should you connect them?

In series

A positively charged piece of plastic exerts an attractive force on an electrically neutral piece of paper. This is because

Charges can be polarized

Applying a charge by touching a charged object to a neutral object is

Conduction

An electric _______ allows charge to easily move through it

Conductor

What is the SI unit of charge?

Coulomb, C

An ohmic conductors carrying a current. The cross-sectional area of the wire changes from one end of the wire to the other. Which of the following quantities vary along the wire?

Electric field

Two lab partners are doing a static electricity investigation. They begin with a neutral pop can. After conducting the procedure, they observe that the pop can has become charged negatively. Which statement accurately explains how this happened?

Electrons are added to the object

Which of the following best describes the inner workings of conductors?

Electrons collide at random, experiencing a net change of position equal to zero, except when exposed to an external electric field

The combination of two separated point charges of opposite sign but equal magnitude is called an

electric dipole

The electric force acting on a test charge (q) at a point divided by the value of the charge is the

electric field acting on the test charge

The charge carries in metals are

electrons

A region with parallel electric field lines has a constant electric potential

false

Electric field lines close together indicate weak electric field strength

false

a negative charge, if free, will tend to move

from low potential to high potential

In a certain region of space, a uniform electric field is in the x direction. A particle with negative charge is carried form x=20.0 cm to x=60.0 cm. The electric potential energy of the charge field system

increases

electron's kinetic energy

increases

the proton's kinetic energy

increases

The electric field midway between equal positive and negative charges

is twice as strong as the field of one charge alone and points toward the negative charge

The electric field caused by the charged plates points

towards the negative plate

The static electric field inside an object made from a conducing material is

zero everywhere