EDZA VIRTUAL LAB · CURRENT ELECTRICITY

Meter bridge

Determine an unknown resistance using the Wheatstone bridge principle. Set the resistance box, close the key, and locate the null point.

Class XII PhysicsExperiment 02 / Resistance measurement
EXPERIMENTAL SETUP

Meter bridge

Circuit open
Meter bridge laboratory apparatus A wooden meter bridge with copper strips and a stretched resistance wire, connected to a wound unknown resistance, a resistance box, an analog galvanometer, a two volt battery and a brass key. Drag the jockey along the ruler. The key and resistance box can also be operated directly. EDZA AI VIRTUAL LAB / ELECTRICAL MEASUREMENTS RESISTANCE COIL UNKNOWN · X 5.0 Ω RANGE 1–20 Ω RESISTANCE BOX 0 −20+20 G CENTRE ZERO · mA DC GALVANOMETER LAB CELL 2 V · DC +− KEY K X = 6.0 Ω R = 5.0 Ω cm A B METER BRIDGE · 100 cm · UNIFORM WIRE UNKNOWN RESISTANCE RESISTANCE BOX JOCKEY · 50.0 cm Drag the black jockey handle along the wire · click the brass key to open or close the circuit

Interactive apparatus · On smaller screens, scroll sideways to inspect the full setup.

50.0 cm
A · 0 cm100 cm · B
Fine adjustment
GALVANOMETER CURRENT0.000 mA
Close the key to begin.
THE METHOD

Procedure

  1. 01
    Set up the bridge

    Choose R and close key K to connect the battery.

  2. 02
    Look for the null point

    Move the jockey until the galvanometer reads approximately zero. Use fine adjustment near balance.

  3. 03
    Record, repeat, calculate

    Record at least three readings using different values of R, then find the mean resistance.

THE SCIENCE BEHIND IT

At balance, no current flows through G.

A uniform wire has resistance proportional to its length. At the null point, the two junctions have the same potential.

X = R × l100 − l

X is in the left gap. l is measured from end A, in cm.

At this position: X ≈ 5.00 Ω Valid only at balance
Model assumptions & precautions

This simulation uses a uniform 100 cm wire (2 Ω total), an ideal 2 V source, and a 100 Ω galvanometer. Lead and contact resistances are neglected. In a real lab, touch the jockey gently; do not slide it while pressing. Open the key between readings to avoid heating. Swapping gaps helps check end errors in a real bridge.

The green null window is ±0.15 cm around the exact balance point, representing finite position resolution. Recorded results can therefore differ slightly from X.

YOUR EXPERIMENTAL NOTEBOOK

Observations 0 readings

TRIALKNOWN R (Ω)GAP OF Xl (cm)100 − l (cm)CALCULATED X (Ω)
≋No observations recorded.

Balance the bridge, then record your observation.

MEAN RESISTANCE— Ω

Collect readings with different R values for a reliable result.

WELCOME TO EDZA VIRTUAL LAB

Your experiment, step by step.

Your goal is to find the resistance X by balancing a Wheatstone bridge.

  1. Choose a known resistance R using the control panel.
  2. Click Close key to supply power.
  3. Drag the black jockey or move its slider. Arrow keys adjust by 0.1 cm; Home/End move to the limits.
  4. Find the green Bridge balanced indicator and record the reading.
  5. Change R and repeat. Aim for three different values with null points near the middle of the wire.
  6. Try Challenge mode for circuit assembly, independent resistance calculations, series/parallel verification, and viva practice. Each mission starts a fresh notebook.

A zero reading with the key open is not a balance measurement. The experiment must be powered to record.