Physics Ch. 22 – Flashcards

Electricity at rest, "static electricity"

wide range of electrical phenomena that (in one form or another) underlie everything around us. Lightning, match strike spark, bonds between atoms, molecules

The electric force between Earth and Moon cancels out because they have an equal number of positive and negative charges.

The nucleus is positively charged and the electron cloud is negatively charged.

All electrons have the same charge. Electron charge is equal and opposite to the proton charge. A proton has 1800 times the mass of an electron.

Neutral Atoms usually have as many electrons as protons, so the atom has a zero net charge.

A positive ion is a neutral atom that has lost one or more electrons. A negative ion is a neutral atom that has gained one or more electrons.

Net charge cannot be created or destroyed.

All charged objects have a charge that is an integer multiple of the charge of an electron. There is no smaller units of charge (than one electron/proton) observed!

Proton or electron

1 C is associated with 6.25 × 1018 electrons. That's *6.25 billion billion* electrons!

Newton's law of gravitation is attractive, whereas Coulomb's law is attractive or repulsive. Both are proportional to the inverse square of distance.

The outer shell electrons in metals are free to move from atom to atom. "loose" outer shell e-

Electrons are tightly bound to their atoms, making them poor conductors of heat. The outer electrons belong to particular atoms.

A semiconductor is neither a good conductor nor a good insulator - it has a middle range of resistivity. fair insulator in pure crystalline form, excellent conductor when e- added or removed

A transistor is made of thin layers of semiconducting materials sandwiched together. It can be a switch, an oscillator, or an amplifier. Behaves as both conductor and insulator (thus on/off switch, up/down amplifier)

ordinary conductors have a small resistance to the flow of electric charge, but Superconductors have infinite conductivity (current flows forever)

Electrons transfer from one place to another.

Charging by friction occurs. Electrons are transferred when one object rubs against another. *same with socks on carpet!

Ice crystals are charged by friction and the ground is charged by induction. as warm water vapor rises in the air, it brushes against ice crystals high in the air above, producing a charge (friction).

To prevent a fire caused by lightning. If sufficient charge does not leak from air to rod, charge will attract to the rod and direct to the ground instead of building.

An electrically polarized object can have zero net charge, while a charged object cannot have zero net charge. Polarized: one side of atom is more +, other side is more -. Charged: entire atom is either + or - charged.

In an electric dipole, positive and negative charges are separated on opposite sides of an object. Distribution of electric charge is not perfectly even.

water molecules!

Gravity fields made by mass, electric fields made by charge

The direction of the field is the direction of the force on a positive test charge.

Because of mutual repulsion, mobile electrons in the conductor will spread out uniformly over the outer surface of the ball, so the force and the field on a test charge at the center is zero because opposing forces balance in every direction.

The charges arrange themselves to make the field inside the conductor zero. ex.) in sphere, in car

1.5 joules 1 volt = 1 joule/coulomb

No. Energy is voltage times charge, so you need a coulomb of charge to get several thousand joules of energy. Difference between electric potential energy and electric potential.

The energy is stored in the electric field between the plates. (figure 22.26)

the electrons move around the neucles in which the protons and neutrons are bounded by the strong neuclear force. e-s which are faraway from necucles are free from electrosatic attraction of the necucles moreover due to less mass they feel high acceleration for same force ....... hence only these e-s are able to move and conduct

Place a strong positive charge close to, but do not touch the object to be charged. This pushes the negative charges to the other side of the object. Connect a wire(that is connected to the ground) to the object. The negative charges(electrons) will flow out of the object into the ground. Disconnect the wire. The object is positively charged.

Coulomb's force is much 'stronger' than Gravitation. If 2 objects are repelled from each other due to electrical repulsion, they would have to be VERY massive (in relation to the small electric potential causing the repulsion) in order for the Gravitational force to cancel out the Coulomb force.

Because a proton has A LOT more mass than an electron. Newton's law F=ma indicates acceleration is related to the mass of the object having the force exerted on it. Since the force is the same in both cases, the acceleration must be lower for the proton because it's mass is higher. I'll show an example where the numbers are no where near real, but it will show the relationship: Proton: F=100 m=20 therefore, a = 5 Electron F=100 m=5 therefore a=20 Notice how (m) times (a) must equal the same value in both cases? That's what's causing the electron to move so much faster, because it's so much less massive.

It's because you are pretty much completely enclosed by a conducting shell formed by the car body. It's called a "Faraday cage." The electric field inside a conducting shell is zero no matter what goes on outside. When there are holes in the shell (as for the car windows) then the field isn't exactly zero but it is greatly reduced from the outside value. This is related to the shielding effect of the metal full of holes in a microwave oven door. The charge spreads out over the roof surface. As long as you do not touch the roof! There is still a small charge that will hit the car.

A capacitor is used to store charge. It does this by the means of an electrochemical reaction. After the charging circuit is turned off, this charge - if not discharged by any means - is still present in the capacitor. High-Voltage capacitors can amass sufficient current for it to be lethal at said voltage, and they can deliver all of it at the slightest contact.