Electrostatics Flashcards
Electric force
- like kinds repel and unlike kinds attract - when two+ atoms join to form a molecule, the molecule contains balanced positives and negatives
Electric charges
- Positive 2. Negative 3. Neutrons
Atom facts
- every atom is composed of a positively charged nucleus surrounded by negatively charged electrons - electrons of all atoms are identical - atoms usually have as many electrons as protons, so the atom has zero net charge
Conservation of charge
When we charge something, no electrons are created or destroyed, they are just transferred from one material to another - charge is conserved
Coulomb’s law
The electrical force decreases inversely as the square of the distance between charged bodies F = k (Q1Q2/d^2) K = 9 x 10^9 N x m^2 /C^2 Electrical forces may be either attractive or repulsive, whereas gravitational forces are only attractive
Conductors
(Good conductors) materials where the electron in the outer shell of the atoms is not anchored to the nuclei of particular atoms but is free to wander in the material - metal
Insulators
(Poor conductors) materials where the electrons are tightly bound and belong to particular atoms - rubber, glass
Semiconductors
Material that can be made to behave sometimes as an insulator and sometimes as a conductor
Transistors
Made of thin layers of semiconducting materials sandwiched together - they are used to control the flow of currents in circuits, detect and amplify radio signals, and to produce oscillations in transmitters - they require little power
Super conductors
Materials that acquire zero resistance (infinite conductivity) to the flow of charge - occurs at suffice Nelly low or high temperatures
Charging by friction
Electrons transferred by friction when materials rub against each other
Charging by contact
Negatively charged object contacts a neutral object and electrons move to the neutral object
Charging by induction
Redistribution of electric charges by the electrical influence of a charge object close by but not in contact - lightning rod
Electrically polarized
When charges of an atom or molecule are aligned so that one side has a slight excess of positive charge and the other side a slight excess of negative charge
Electric field
The space around every electrically charged body - contains: magnitude (force per unit charge at any point) and distance (E = F / q) E = electric field at that point F = force at some point in space Q = charge of the body
Electric field facts
- direction of the field is defined to be the direction on which a mall positive test charge at rest would be pushed - the electric field is a storehouse of energy - electric fields can be shielded by various materials
Electric shield wants
If we want to shield an electric field, whatever is needing to be shielded is surrounded with a conducting surface. When this surface is placed in an electric field, the free chargers in the conducting surface will arrange themselves on the surface of the conductor so that all field contributions inside cancel one another
Electric potential
Work is required to push a changed particle against the electric field of a charged body - this will change the electric potential of the particle - electric potential does not equal potential energy - a high electric potential (voltage) means a lot of energy only if a lot of charge is involved - electric potential (aka voltage) = potential energy per unit charge Electrical potential = electic potential energy / charge
Electric charge unit
Volt 1 volt = 1 joule of energy per 1 coulomb of charge
