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Edexcel A Level Physics:復習筆記3.6 Resistance in Series & Parallel

Category: A-level課程, 教材筆記, 福利干貨 Date: 2022年10月9日上午9:44

When two or more components are connected in series:
- The combined resistance of the components is equal to the sum of individual resistances

10.1.2.4-Resistors-in-series-diagram

Resistors connected in series

The equation for combined resistors in series is derived using the electric current rule and the electrical voltages rule
These rules describe that for a series circuit:
- The current is the same through all resistors
- The potential difference is? split between all the resistors

3-6-derivation-resistors-in-series_edexcel-a-level-physics-rn

10.1.2.4-Resistors-in-series-equation

In a parallel circuit, the combined resistance of the components requires the use of?reciprocals
- the reciprocal of the combined resistance of two or more resistors is the sum of the reciprocals of the individual resistances
  Resistors connected in parallel
The equation for combined resistors in series is derived using the electric current rule and the electrical voltages rule
These rules describe that for a parallel circuit:
- The current is the split at the junction (and therefore between resistors)
- The potential difference is the same across all resistors

3-6-derivation-resistors-in-parallel_edexcel-a-level-physics-rn

10.1.2.6-Resistors-in-parallel-equation

This means the combined resistance decreases
- The combined resistance is? less than the resistance of any of the individual components
- For example, If two resistors of equal resistance are connected in parallel, then the combined resistance will halve

The combined resistance?R?in the following series circuit is 60 Ω. WE-Resistors-in-series-question-image

Wich of the following is the value of R2?

A.? ? ?100 Ω? ? ? ? ? ? ? ?B.? ? ?30 Ω? ? ? ? ? ? ? ?C.? ? ?20 Ω? ? ? ? ? ? ? ?D.? ? ?40 Ω

WE-Resistors-in-series-answer-image

WE-Resistors-in-parallel-question-image-1

WE-Resistors-in-parallel-answer-image

The most common mistake is to forget to find the correct value for RT in parallel. Remember to do ?to get the correct value.

Reciprocals can be considered in the following way:

The reciprocal of a value is
- For example, the reciprocal of a whole number such as 2 equals
- The reciprocal of ?is 2
If the number is already a fraction, the numerator and denominator are ‘flipped’ round

10.1.2.6-Reciprocals

The reciprocal of a number is 1 ÷ number

In the case of the resistance R, this becomes
To get the value of R from , you must do
You can also use the reciprocal button on your calculator (labelled either or , depending on your calculator)