Unit D Section 2.1 Flashcards
Insulators
are materials that do not let electricity flow easily.
Electrons in insulators are tightly bound to the positive nucleus of their atoms. They resist moving away from the nucleus.
Ex. Plastic or silk or air
Conductors
are materials that are easy for electrons to flow.
In conductors, the electrons are not as tightly bound. They are freer to move.
But electrons move when voltage is applied.
However, a current will flow only when the conductor is connected to an electrical source. The electrons then move toward the positive end of the voltage source.
Ex. steel or silver
Semiconductors/partial conductors:
they are materials that have conductivity between conductors and insulators.
Ex. Germanium and silicon
At high temperatures, they act like conductors. At low temperatures, they act like insulators.
Superconductors
they are perfect conductors because unlike most conductors, electrons do not experience resistance.
They can pass the current very quickly and can stand high charges.
Ex. Mercury is a perfect conductor, with no resistance to current flow.
Since that time, substances have been found to superconduct at temperatures well above absolute zero. But still too low for practical applications.
Resistors
The resistor is a kind of conductor.
What is the purpose of resisters?
A resistor limits the amount of current because it allows electricity to pass but provides resistance.
. Resistance is a measure of how difficult it is for electrons to flow through a substance or something that interrupts or reduces the flow of electrons
Less resistence=?
more current
More resistance=?
less current
The unit of resistance
= ohms/ omega ( Ω ).
What happens when the more resistance a substance has
the more the substance gains energy from each electron that passes through it. The energy gained by the substance is radiated to its surroundings as either heat or light energy.
Ex. a lightbulb and heater.
How is the light bulb lit or a heater turns on?
The more resistance a substance has, the more the substance gains energy from each electron that passes through it. The energy gained by the substance is radiated to its surroundings as either heat or light energy.
Ex. a lightbulb and heater.
How can solutions be resistors?
Solutions can be resistors because if solutions contain charged particles, they can conduct.
Other applications of resistance:
The polygraph machine or “lie detector” is another application of resistance
It usually measures skin resistance, blood pressure, and respiration.
To measure this change, two or more metal electrodes are attached to the skin of the person taking the test.
Thus, a lie should cause an increase in conduction between the electrodes.
What is a variable resistor:
A variable resistor or rheostat is a type of controlling device.
They don’t completely turn off or on but gradually change the amount of current.
Rheostats can increase or decrease the amount of current in a circuit by adjusting the portion of the resistor that the current travels through.
Ex. volume of device and speed controls
Describe the form of switches:
Switches are used for turning electricity in a circuit off and on.
Switches are enclosed in an insulated casing or a metal box to prevent shocks and short circuits. It also keeps dust and other contaminants out of the switch mechanism.
