- Electrical resistance is a little like friction and electrons flowing in wires lose energy overcoming it.
- All conductors have some resistance and the larger the resistance, the larger the amount of energy dissipated within it as electrons flow, and therefore, the greater the energy needed to move electrons around a circuit.
- Hence, if a fixed voltage supply is connected to a circuit with a low overall resistance more current (i.e. coulombs of charge per second) will flow than if the same supply is connected to a higher resistance circuit.
- Some electrical components, such as water heaters, are designed to have a large resistance so that a lot of electrical energy is converted into heat as current flows through them.
- Wires and cables on the other hand should have a low resistance so that not much energy is lost when electricity is supplied from one place to the other.
- The unit of resistance (R) is the ohm (Ω) and one ohm is the resistance that causes a drop of one volt when a current of one ampere flows.
- For a metallic conductor which remains at a Constance temperature Ohm's law applies:
Components in circuits that are designed to have a fixed resistance are usually shown as a simple
box, as depicted in figure 2.1.
An electrical heater is used on a 240V supply draws a current of 12A. Its resistance is:
R=U/I=240/12=20ohms.
0 comments:
Post a Comment