Key relationship
r=ρℓ/A; empirical ρ(T)=ρ20/[1+0.02(T−20)]; Vterm=E−Ir.
Physics · Practical apparatus
Cell EMF and internal factors
Read open-circuit voltage first, then close the load switch and observe terminal drop. Vary electrode spacing or immersed area to change internal resistance while holding the assigned EMF fixed.
Open the interactive experiment →Cell EMF and internal factors
முதலில் திறந்த சுற்று EMFஐ வாசித்து பின்னர் சுமையுடன் முனை மின்னழுத்தத்தைக் கவனிக்கவும். பரப்பும் இடைவெளியும் உள் மின்தடையை மாற்றும்.
Key notes, relationships and model limits
Practical tip
Read open-circuit voltage first, then close the load switch and observe terminal drop. Vary electrode spacing or immersed area to change internal resistance while holding the assigned EMF fixed.
Common trap
Changing geometry need not change the assigned chemical EMF.
Model limits
Assigned constant chemical EMF; uniform electrolyte geometry; empirical temperature trend. Polarization, concentration changes and actual electrochemistry omitted.
What you will learn
Separate EMF from internal-resistance factors.
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
ρ10 Ωcm,ℓ2 cm,A20 cm² gives r1 Ω; E1.5 V,R10 Ω gives Vterm≈1.364 V.
Why this matters
The model connects cell emf and internal factors with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
In this geometry model, doubling electrode area changes r to?
- Twice
- Half
- Unchanged
Read the explanation
r is inversely proportional to area.
Course connection: Virtual apparatus preparation. Check exact board/exam membership in the syllabus sources. Physical practical work remains necessary.