Physics Chapter 18

What is an electric field?

An electric field is an area where the electrical forces act on a charged object.

What is the unit for charge?

Coulomb (C)

What happens to the the charge distribution of a neutral metal sphere when a positively charged plastic tube is placed nearby?

The negative charge in the sphere is attracted to the positive charge in the tube.

A negatively charged balloon is brought near a neutral conducting sphere. As it approaches, the charge within the sphere will distribute itself in what very specific manner?

*Image C.* The balloon does not touch the sphere meaning that the sphere remains neutral, but the electrons will be repelled to the other side of the sphere.

What are the 3 different ways an object can become charged? How do they differ from one another?

1. *Friction* - when objects contact and surfaces rub together, objects that started out as neutral gain charge due to electron affinity. 2. *Induction* - when a charged object is brought near an uncharged object, but they do not touch. 3. *Conduction* - when a charge object is touched to an uncharged object and electrons are transferred.

In physics and electrical charges, what does the term ground mean? Why is grounding important?

A ground has an infinite supply of electrons and is useful for balancing out the charge of any charged object to make it neutral. Grounding is important because it neutralizes charges which could be dangerous in different situations.

A neutral metal sphere is touched by a negatively charged metal rod. As a result, the sphere will be ____ and the metal rod will be ____.

A neutral metal sphere is touched by a negatively charged metal rod. As a result, the sphere will be *negatively charged* and the metal rod will be *negatively charged*.

If there are 8.25749 x 10^17 protons and 5.26 x 10^14 electrons; the charge on this object is ____ Coulombs.

Charge = positive (there are more protons than electrons) Quantity = 0.13 C (subtract the number of electrons from the protons, then multiply the number of protons by the charge of one proton)

Determine the quantity and type of charge on an object that has 3.62 x 10^12 more protons than electrons.

Charge = positive (there are more protons than electrons) Quantity = 5.8 x 10^-7 C (multiply the number of protons by the charge of one proton)

In charged objects, which subatomic particle is actually moving from object to object?

Electrons. (protons and neutrons are fixed to the nucleus and cannot move freely)

What is electrostatic equilibrium?

Electrostatic equilibrium is what is reached when the charges are balanced out and no longer move (meaning that they are not moving toward or away from each other).

True or false? An object that becomes grounded gains neutrons during the grounding process.

False.

A 0.90-gram balloon with a charge of -75 nC is located a distance of 12 cm above a plastic golf tube that has a charge of -83 nC. Find the net force and acceleration of this system.

Force is 0.00389 N. Acceleration is 4.32 m/s/s.

What do each of the variables in Coulomb's Law equation stand for?

K = a constant equal to 9x10^9 in air (it is a measure of air conductivity) Q = the charges of two objects F = the electrical force between two objects D = the distances between the center of mass of two charged objects

Why does a rubber rod become negatively charged when rubbed against fur?

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

What is electrical force measured in?

Newtons (N)

Is electrical force a contact force?

No, it is a long distance force.

If you place a sweater next to a balloon and the electrons move from the sweater to the balloon, which has a greater electron affinity? How can you tell?

The balloon has a greater electron affinity. Electron affinity means that the object attracts electrons to itself so if the balloon gains a negative charge, that means the electrons traveled from the sweater to the balloon because it has a higher affinity for the electrons.

What happens when a charged object comes into contact with a neutral object?

The charged object will be attracted to the neutral object because electrons will move, causing the attraction.

What is the difference between a conductor and an insulator?

The electrons found in a more conductive material are more free to move around than those found in an insulative material.

A positively charged balloon is brought near a neutral conducting sphere. While the balloon is near, the sphere is touched (grounded). How will the electrons move?

The electrons will move into the sphere from the ground (hand).

What is electrical force?

The force experienced by a charged object. This force can either attract or repel and depends on the charges involved.

How does electrical field intensity relate to the density of electrical field lines?

The higher the density the stronger the intensity.

What does it mean for an object to be polarized?

There is a positive charge on one side of the object and a negative charge found on the other side.

Determine the electrical force of attraction between two balloons with separate charges of +3.5 x 10^-8 C and -2.9 x 10^-8 C when separated by a distance of 0.65 m.

There is an attractive force of 2.16x10^-5 N.

In an electrical field diagram, what does it mean when the arrows are pointed towards an object? What about away?

When the vectors are pointed towards an object it means the object has a negative charge. When the vectors are pointed away it means the object has a positive charge.

Where would you expect an electrical field vector to have the greatest strength?

Wherever it is closer to the charged object.

Is electrical force a vector?

Yes.

A metal sphere has a neutral charge. It is touched by a positively charged metal rod. As a result, the metal sphere becomes charged positively. Which of the following occur during the process? a. The metal sphere gains some protons. b. Electrons are transferred from the sphere to the rod. c. The metal sphere loses electrons. d. The overall charge of the system is conserved. e. Protons are transferred from the rod to the sphere. f. Positive electrons are moved between the two objects.

b. Electrons are transferred from the sphere to the rod. c. The metal sphere loses electrons. d. The overall charge of the system is conserved.

What is the charge of a single electron?

negative 1.6 x 10^-19 C