Resistance
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The idea
A thin, long wire makes it harder for the current than a short, thick one. In the water picture: less water flows through a long, narrow pipe than through a short, wide one. How strongly a part hinders the current is told by the resistance.
What to remember
- Resistance
The electrical resistance says how strongly a part hinders the current. Its symbol is and it is measured in ohms (Ω).
At the same voltage: the larger the resistance, the smaller the current.
| Change to the wire | Resistance |
|---|---|
| longer | gets larger |
| shorter | gets smaller |
| thicker | gets smaller |
| thinner | gets larger |
| other material | copper has a small resistance, constantan a large one |
Resistor as a part
A part built in on purpose for its resistance is also called a resistor. Its circuit symbol is a rectangle.
Example
The long cable
Two copper cables are equally thick. One is 1 m long, the other 10 m. The long cable has the larger resistance. That is why less current gets through a cable drum that is fully unrolled.
Practice
Task no. 1
Task no. 1
At the start the ammeter shows 0.12 A. Set the length and thickness of the wire so that it shows at least 3 times as much.
The wire is 5 m long and 0.1 mm² thick at the start. You can set the length from 1 to 6 m and the thickness from 0.1 to 0.5 mm². The battery has 3 V.
Solution
A shorter or thicker wire has less resistance, so more current flows: half as long or twice as thick gives twice the current. For example 1 m long and 0.5 mm² thick: then 25 times as much flows.
Exercise
Solution
the 2 m one right answer
The longer the wire, the larger the resistance.
the 1 m one
The shorter wire has the smaller resistance.
both the same
With the same material and thickness the length matters, and it differs.
The longer the wire, the larger the resistance.
More on it:
Exercise
Solution
a shorter wire right answer
Less length, less resistance.
a thicker wire right answer
A thick wire gives the current more room, so the resistance falls.
a longer wire
A longer wire has a larger resistance.
a thinner wire
A thinner wire has a larger resistance.
Shorter and thicker make the resistance smaller, longer and thinner make it larger.
More on it:
Exercise
Solution
Right answer: 1. wire of 0.2 mm diameter, 2. wire of 0.5 mm diameter, 3. wire of 1 mm diameter, 4. wire of 2 mm diameter
The thinner the wire, the larger the resistance: the thinnest wire comes first.
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