Honors Physics 2 Quiz 1

What parts make up the atom?

Protons (positive charge) and Neutrons (neutral/no charge) are found compacted in the nucleus of the atom. It has the smallest volume but the most mass in the atom.

Electrons are negatively charged and take up most of the volume but almost none of the mass.

If there are an equal amount of protons and electrons in an atom, there is no charge and it is neutral. It cancels out.

What are the units used for energy called?

The SI unit for charge is called Coulombs ©.

Electrons have a negative charge of (- 1.6x10^-19)

Protons have a positive charge of (1.6x10^-19)

How do you give something a charge in general?

Electrons are present in the space outside the nucleus. They are negative charges and weakly bound to the atom. Electrons are often removed from the atom and transferred to a new one every day normally. You can do this by rubbing and scraping things together.

You cannot really take away and remove protons from an atom. That would be nuclear fission and takes a lot of energy.

You create a charge when there is an imbalance of protons and electrons. More electrons means negative charge, more protons means positive charge. An even amount of protons and electrons is an equal charge. The world tends to usually stay neutral if things are not properly grounded there is a static charge.

Equation for charge:

Charge is always an integer multiple of the charge of the electron. We say charge is quantized. It must be a multiple of that value.

Equation: Q=Ne—----- Q is the net charge (of proton or electron), N is any integer, e is the charge of the proton or electron + for proton - for electron.

Electrostatic Force: When do charges attract and when do they repell?

Two of the same charge (2 positive charges when close together) or (two negative charges when close together) repel each other when they get close.

Two opposite forces (a negative and a positive force) will attract each other and become neutral.

A charged force and a neutral force will also attract each other. You might not know if the charged force is positive or negative but there are ways to test. You can bring a known positive or negative force near and see if it repels or attracts, if it attracts it is the opposite of the force you brought close by.

What motivates electrons to move: electrons repel one another the closer they are the stronger the repulsion.

Why don't protons repel eachother and stay compacted in the nucleus?

The reason protons don't repel each other in the nucleus and stay compacted is the nuclear force and the neutrons calm things down and keep the nucleus stable so they don't repel.

Conductors and Insulators: What is it, what is the spectrum, give some examples.

All matter falls along the spectrum between insulting and conducting electrons.

It is a spectrum to show how easily electrons move through and around the material.

Conductors: They have electrons that are not tightly bound to one atom they like to flow and move around and they transfer easily. When a charge is placed on an object those electrons quickly spread out. Some examples of conductors are: Iron, copper, silver, and metals, some okay ones are carbon, human body, salt water.

A semiconductor is a material with electrical conductivity between that of a conductor (like metal) and an insulator (like rubber). Its ability to control and switch electrical current makes it essential for modern electronics. You can control the charge.

Insulators: This material has electrons tightly bound to a specific atom. Any charge transferred to an insulator tends to stay in that space instead of spreading out. Some examples of this is wood, glass, dry air, rubber, plastic, paper, silk, wool.

Methods of Charging: explain friction

Friction: "Electrons are transferred from [material that loses] to [material that gains], leaving the first object positively charged and the second object negatively charged." Both objects start neutral. Then you rub them together to exchange electrons then one becomes positive and one becomes negative. When you rub two of the triboelectric series together the items on the higher end of the list will take electrons lower on the list.

Methods of charging: explain conduction

Conduction (contact): "Electrons move from the charged object to the neutral object until both objects are charged with the same sign." If you have contact with a neutral and a negative object the electrons will take a path towards the neutral object and give electrons to the neutral object making it negative. The negative object is less negative and the neutral object is more negative. They are spreading out. It's not conducting anything, it is just spreading out/transferring. Not a constant flow. One starts neutral and one is charged, electrons from the charged object move to the neutral object making it the same charged.

Methods of charging: explain induction

Induction: "Electrons in the neutral object are repelled/attracted by the nearby charged object. When grounded, electrons flow [into/out of] the object. After the ground is removed, the object is left with a net charge opposite to the nearby charged object." Let's say you have a neutral object, and a negative metal is nearby and doesn't touch, the neutral object will polarize. If you give the polarized object a path to the ground or another way out, it gives a path for electrons to escape because they do not like the negative charge and do not want to be by each other. They leave through the path. Now when the electrons leave the neutral object is now positive. When you put a positive force near the neutral object it gets polarized, if you add a wire from the ground electrons will come into the neutral object because they are attracted to the positive force and now you added electrons so it is overall negative. You start with one neutral object and one charged nearby. Ends up with two oppositely charged objects.

Explain what grounding is

Grounding: When a charged object is grounded, electrons either flow from the object into the Earth (if the object has extra negative charge) or from the Earth into the object (if the object is positively charged). It will make the object neutral. Ex. The sphere has extra electrons, giving it a negative charge. You connect the sphere to the Earth using a metal wire (or just touch it with your hand). Electrons flow from the sphere into the Earth because like charges repel, and the Earth can accept an unlimited number of electrons. After some electrons leave, the sphere is neutral

Polarization:

On a conductor the electrons will freely move, and will move in the presence of a charged object even if they are not touching.

The object remains neutral; it is polarized. The charges are separated into opposite ends.

If a positive object is near a neutral object the electrons will move closer to the possible object leaving the protons behind, but that object is still neutral.

If a negative object is near a neutral object the electrons leave the area near the negative charge and the protons stay near the negative charge attracting it.

conduct and valence band: what is it? how does it work in each part of the spectrum?

There is a conduct and valence band in insulators, semiconductors, and conductors, the distance between the two tells you how much energy is needed for the electrons to move.

1. Conductors (like metals)

Valence band = highest band filled with electrons.

Conduction band = overlaps with the valence band (or is partially filled).

Result: Electrons can move freely because they don't need extra energy to jump bands → good electrical conductivity.

2. Semiconductors (like silicon)

Valence band = filled at low temperature.

Conduction band = empty at low temperature.

Band gap = small (~1 eV).

Result: With a little energy (heat, light, doping), electrons jump from valence to conduction band → conductivity can be controlled.

3. Insulators (like glass, rubber)

Valence band = completely filled.

Conduction band = completely empty.Band gap = very large (usually > 4 eV).

Result: Electrons cannot gain enough energy to cross the gap → no conductivity.