# Resistance, wire thickness, fuses, current -- Confusion

1. Feb 17, 2015

### Barclay

1. The problem statement, all variables and given/known data

In a book discussing a simple electrical circuit it said "If a thick wire is used in the experiment, the current will be extremely high for a very low voltage. The wire can get very hot very quickly".

This got me thinking about fuses in plugs. Is the fuse in a plug a thick wire so that it becomes hot a blows readily? I always thought it was a thin wire.

The statement made by the book is correct because:

resistance of wire ∝ 1/cross-sectional area

So as the wire thickens it's resistance decreases (so it is a low resistance wire).

V = IR

R 1/ I So because the resistance of this thick piece of wire is low it will take in high current and get hot.

Or was I correct earlier when I thought that fuse wires are normally thin compared to the rest of the circuit so that they do not get hot and blow too readily?

2. Relevant equations

3. The attempt at a solution

2. Feb 17, 2015

### Staff: Mentor

The wire in fuses is sized to blow for a given current and duration. Higher amperage fuses will be thicker than lower amperage fuses.

3. Feb 17, 2015

### lightgrav

A wire gets hot (hot enough to burn skin, or melt its insulation off) because its Thermal Energy must flow thru its surface Area (to outside).
Thick wire carries a similar current density (I/A) as thin wire , for a given local E-field (V/m).
fuse wire is typically thinner than "household wire" so that it gets hot enough to melt itself, carrying only a few Amps.