An example of how this formula can be used:
Question: If we have a 12V battery that is connected to a 2400 W load. How much current is running through the cable? Answer: V = 12V P = 2400W
I = P/V = 2400/12 = 200 A
2.3 Conductivity and resistance
Some materials conduct electricity better than other materials. Materials with a low resistance conduct electricity well, and materials with a high resistance conduct electricity poorly, or not at all. Metals have a low resistance and they conduct electricity well. These materials are called conductors. This is the reason they are used in electrical cables. Plastic or ceramics have a very high resistance, they do not conduct electricity at all. They are called insulators. This why, for example, plastic or rubber is used on the outside of cables. You will not get an electrical shock when you touch the cable. Insulators are also used to prevent short circuit when two cables touch each other.
Each material has its own specific resistance. This is written down as rho (ρ). In Ω.m. The table on the right on the right lists various conducting materials, their electrical conductivity and their specific resistance. You can see in this table that copper conducts electricity well and has a low resistance. This is the reason why electrical cable is made from copper. But, for example, titanium, does not conduct electricity well and therefor has a higher specific resistance. There are two more factors that determine cable resistance. These are the length and the thickness of the conductor (cable):
• A thin cable has a higher resistance than a thick cable • A long cable has a higher resistance than a short cable
The resistance of a length of cable can be calculated:
𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙ℎ𝑡𝑡 /
𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴
𝑙𝑙 /
𝐴𝐴
Resistance = Rho x
R= ρ x
As you can see there are 3 factors that determine cable resistance. Namely: • The electrical resistance of the used material • The length of the cable (longer cable = more resistance) • The diameter of the cable (thinner cable = more resistance)
It is important to know the resistance of a cable. Cable resistance creates two effects when a current is passed through a cable: • There will be a voltage loss over the cables • The cables heat up
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