Key relationship
Rseries=R₁+R₂; Rparallel=R₁R₂/(R₁+R₂).
Physics · Class 12
Resistance combinations
Series elements carry the same current; parallel branches see the same voltage. The equivalent parallel resistance is below the smallest branch resistance.
Open the interactive experiment →Resistance combinations
தொடரில் மின்னோட்டம் சமம்; பக்க இணைப்பில் மின்னழுத்தம் சமம். பக்க இணைப்பின் சம மின்தடை சிறியதாகும்.
Key notes, relationships and model limits
Remember
Series elements carry the same current; parallel branches see the same voltage. The equivalent parallel resistance is below the smallest branch resistance.
Common trap
A parallel equivalent resistance is lower than the smallest branch resistance. Branch currents need not be equal.
Model limits
Two constant, positive ohmic resistances and an ideal voltage supply are used. Wire resistance and temperature changes from heating are omitted.
What you will learn
Use the controls and plotted relation to explain resistance combinations.
Try the experiment
Try both scenarios, change one control, and predict the result before checking the graph and readouts.
Think of it this way
Change one input while keeping the others fixed, as you would in a controlled experiment.
Worked example
The same two resistors give 30 Ω in series and 6.67 Ω in parallel.
Why this matters
The model connects resistance combinations with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
10 Ω and 20 Ω in parallel have equivalent resistance?
- 30 Ω, the sum of the branch resistances.
- 6.67 Ω.
- 15 Ω, their arithmetic mean.
Read the explanation
6.67 Ω.
Course connection: Class XII Chapter 3. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.