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CSEEL shifts education from rote memorization to active inquiry and hands-on experimentation. Students observe, build, analyze, and apply scientific concepts to real-world challenges, developing critical thinking and scientific temper as envisioned by NEP 2020.

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Resistance Combination & Verification using Meter Bridge

Experiment video

What you will learn

Verify the laws of combination of resistances (series and parallel) using a Wheatstone meter bridge apparatus and determine unknown resistances.

Materials needed

Meter Bridge Board with 1m Manganin wire
Meter Bridge Board with 1m Manganin wire
₹50
What is it?
One-meter long manganin or constantan resistance wire tensioned over a graduated wooden meter scale.
Specifications
Wire Length
100.0 cm
Wire Composition
Constantan (60% Cu, 40% Ni)
Strip Thickness
3.0 mm thick copper strips
Base
Teakwood polished board
Leclanché Cell or regulated 2V DC power supply
Leclanché Cell or regulated 2V DC power supply
₹95
What is it?
Decade plug-type resistance box with non-inductively wound manganin coils.
Specifications
Total Resistance
1 – 100 Ω
Accuracy
± 0.1%
Plugs
Heavy brass plugs with taper fit
Base
Ebonite top plate
Sensitive Galvanometer (center zero)
Sensitive Galvanometer (center zero)
₹140
What is it?
Centre-zero dead-beat moving coil galvanometer with high current sensitivity.
Specifications
Scale
30 – 0 – 30 divisions
Current Sensitivity
20 μA / division
Internal Resistance
80 Ω
Terminals
Gold-plated binding posts
Standard Resistance Box (1 to 100 Ω)
Standard Resistance Box (1 to 100 Ω)
₹185
What is it?
Spring-loaded knife-edge sliding contact with insulated handle.
Specifications
Contact Edge
Phosphor bronze knife-edge
Handle
Moulded ebonite grip
Action
Spring-loaded push-to-touch
Terminal
Screw terminal for lead
Jockey with sharp knife edge
Jockey with sharp knife edge
₹230
What is it?
Standard laboratory apparatus used in Resistance Combination & Verification using Meter Bridge.
Specifications
Category
Physics Apparatus
Grade
CBSE / NEP 2020 Laboratory Standard
Two standard resistance coils (R1 ≈ 2Ω, R2 ≈ 3Ω)
Two standard resistance coils (R1 ≈ 2Ω, R2 ≈ 3Ω)
₹275
What is it?
Standard laboratory apparatus used in Resistance Combination & Verification using Meter Bridge.
Specifications
Category
Physics Apparatus
Grade
CBSE / NEP 2020 Laboratory Standard
One-way key and thick copper connecting strips set
One-way key and thick copper connecting strips set
₹320
What is it?
Standard laboratory apparatus used in Resistance Combination & Verification using Meter Bridge.
Specifications
Category
Physics Apparatus
Grade
CBSE / NEP 2020 Laboratory Standard

Tick items as you collect them. Tap + to see the product, specifications and buy options.

Stay safe

Do not drag or scrape the jockey along the bridge wire; touch it gently to prevent non-uniform wire cross-section.
Ensure balance point lies near the center (between 40 cm and 60 cm) for maximum bridge sensitivity.
Clean connecting terminals and tighten screws with pliers.
Use shunt across galvanometer during initial rough balance.

Steps

0 of 7 steps done

1Connect the meter bridge circuit strictly according to Wheatstone bridge principles.
Observation
Heavy copper boundary strips cleaned with sandpaper to eliminate contact resistance at terminal joints.
Safety
Disconnect battery eliminator key while setting up bridge connections.
2Introduce a resistance R from the resistance box in the left gap and unknown coil X in the right gap.
Observation
Null test: Touching jockey at left end gives left deflection; touching right gives right deflection.
Safety
Never drag the jockey knife-edge along the wire; tap gently to avoid scraping or thinning the wire.
3Touch the jockey at 0 cm and 100 cm of the bridge wire to verify opposite deflections in the galvanometer.
Observation
Unplug 2.0 Ω from box; jockey tapped along wire until galvanometer needle stays exactly at zero division.
Safety
Hold jockey by its insulated ebonite handle.
4Gently slide the jockey along the manganin wire until the galvanometer indicates zero deflection (null point l).
Observation
Null length l reads 40.0 cm; calculated unknown resistance X = 2.0 × (60.0/40.0) = 3.00 Ω.
Safety
Release jockey contact between trials to prevent local wire heating.
5Calculate unknown resistance X = R × (100 - l) / l.
Observation
Connect both coils in series end-to-end; null point shifts to 44.4 cm with R = 4.0 Ω.
Safety
Ensure inter-coil series joint is twisted tight or clamped securely.
6Repeat the determination with R1 and R2 connected in series, then in parallel.
Observation
Experimental Rs = 5.01 Ω confirms theoretical addition law within 0.2% tolerance.
Safety
Disconnect battery plug upon completing measurements.
7Compare the experimental combination values with theoretical series and parallel formulas.

Tap + on a step to see what you will observe and any safety tips.

Record your observations

Resistance in Box R (Ω)	Balancing Length l (cm)	100 - l (cm)	Unknown X = R(100-l)/l (Ω)
2.0 Ω	40.0 cm	60.0 cm	3.00 Ω (R1)
2.0 Ω	50.0 cm	50.0 cm	2.00 Ω (R2)
4.0 Ω	44.4 cm	55.6 cm	5.01 Ω (Rs Series: R1+R2)
1.0 Ω	45.5 cm	54.5 cm	1.20 Ω (Rp Parallel: R1R2/(R1+R2))
3.0 Ω	50.0 cm	50.0 cm	3.00 Ω (Repeated test R1)

Tap a highlighted cell to write your own observation.

Result and conclusion

Experimental equivalent resistances for series (Rs = R1 + R2) and parallel (1/Rp = 1/R1 + 1/R2) match theoretical values within an experimental error of < 1.5%.

X = R · (100 - l) / l; Rs = R1 + R2 = 5.0 Ω (Series Verification)

Observation	What it means
Wheatstone Principle	At null deflection, ratio of resistances equals ratio of wire segment lengths (P/Q = R/X).
Series Law Verified	Experimental series resistance Rs = 5.01 Ω matches theoretical R1 + R2 = 3.0 + 2.0 = 5.0 Ω within 0.2%.
Parallel Law Verified	Experimental parallel resistance Rp = 1.20 Ω matches theoretical (3.0 × 2.0) / (3.0 + 2.0) = 1.20 Ω.
Minimal End Error	Balancing lengths obtained near wire center (40–60 cm) minimize meter bridge copper strip end resistance.

Resistance Box (R) vs Balancing Length (l) Characteristic

Sample readings. Replace with your own results.

Experiment photos

Before the experimentDuring the experimentResult