# Resistance

Note by joe saffer, updated more than 1 year ago
 Created by joe saffer about 8 years ago
94
2

### Description

Cambridge IGCSE Physics (electricity) Note on Resistance, created by joe saffer on 05/07/2013.

## Resource summary

### Page 1

Resistance

Resistance is measured in ohms (Ω)  Resistors are used to reduce the current in a circuit Total resistance in series Rt=R1+R2+R3 ......... Total resistance in parallel 1/Rt = 1/R1 +1/R2 + 1/R3 ..........

find the total resistance ----5Ω-----------7Ω-----------5 + 7 = 13and = 13Ω

find the total resistance---------4Ω-|-----8Ω-|---|--6Ω---------|                 |---5Ω---|   |-- 3Ω--3Ω--|

1/Rt = 5/40+8/401/Rt = 13/40Rt    = 40/13Rt    = 3

1/Rt = 1/6+1/61/Rt = 2/6Rt    = 3

Rt = 4+3+3Rt = 10

Resistance of a wire

Electrons collide with and are repelled by ions More collisions = lower current and higher resistance thicker wire = lower resistance  (more room of electrons) longer wire = higher resistance (more ions)

Resistance

Resistance of a wire

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