1 / 21

Controlling the flow

Controlling the flow. Of Electrical Current. Conductors Insulators. Electrons not as tightly bound. They are freer to move. When a conductor is connected to an electrical source, the electrons move toward the positive end of the voltage source.

rio
Download Presentation

Controlling the flow

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Controlling the flow Of Electrical Current

  2. Conductors Insulators • Electrons not as tightly bound. • They are freer to move. • When a conductor is connected to an electrical source, the electrons move toward the positive end of the voltage source. • Electrons tightly bound to the positive nucleus of their atoms. • They resist moving away from the nucleus.

  3. Electrons move when voltage is applied • The atomic structure of a substance affects how well it conducts or insulates. • Some substances are more resistant to electron flow than others.

  4. Semiconductors- at high temp they conduct; low, they insulate

  5. Superconductors • Superconductors are perfect conductors- they have no resistance to electron flow. • Metals such as silver, copper, mercury, and gold are all excellent conductors, but they are not perfect conductors. • Electrons travelling through them still encounter some resistance.

  6. Heike KamerlinghOnnes

  7. The problem with superconductivity • Onnes brought temperature of mercury down to absolute zero using liquid helium, and found was a perfect conductor, with no resistance to current flow. • Substances have been found to superconduct at temperatures above absolute zero, but still to low for any practical applications. • Absolute zero: the lowest temperature that is theoretically possible; • –273.15°C

  8. Electrical Engineers • Need to know how well different materials conduct electricity so they can design devices that are both safe and effective.

  9. resistors • Conductor which allows electric current to pass, but provides resistance to it. • More current flows through a resistor with low resistance, than one with a high resistance. • Resistance is a measure of how difficult it is for electrons to flow through a substance. • Resistance is measured in ohms. science

  10. The Greater the resistance Greater the energy gained. Energy gained by the substance is radiated as heat or light energy.

  11. Solutions can also be resistors • The more charged particles, the greater it conducts. • Tap water & water in the environment are good conductors because they contain dissolved minerals. • Distilled water is not a good conductor because it contains only water molecules.

  12. Lie Detector Test • Polygraph machine is a practical application of resistance. • Measures skin resistance, blood pressure, and respiration; all of these change when people are under stress. • Sweat (salt) contributes to a change in skin resistance. • A lie should cause an increase in conduction between 2 electrodes attached to the skin. • In theory, people sweat more when they lie. • This shows up as a peak on the graph plotted by the polygraph machine.

  13. Switches & variable resistors

  14. Switch • Best method for turning electricity on and off. • When a switch is on, two conductors are pressed together so that current can flow from one to the other. • When the switch is off, the conductors are separated and no current flows. • Most switches are in an insulated casing or a metal box to prevent shocks and short circuits.

  15. Variable Resistor (rheostat) • Sometimes you want to change the current flow gradually in a circuit, instead of just turning it on or off… like you may have a dimmer switch in your home for certain lights. • Rheostats can increase or decrease the amount of current in a circuit by adjusting the the portion of the resistor that the current travels through.

More Related