Wheatstone Bridge, Meter Bridge and Potentiometer
A Wheatstone bridge is balanced when P/Q = R/S; a potentiometer compares potential differences without drawing current at balance.
What is Wheatstone Bridge, Meter Bridge and Potentiometer?
A Wheatstone bridge is balanced when P/Q = R/S; a potentiometer compares potential differences without drawing current at balance.
Key formula / rule: Balance condition: P/Q = R/S; the galvanometer reads zero.
Key points
- Apply the balance condition to determine an unknown resistance.
- Evaluate why null methods are more accurate than direct measurement.
Common exam trap
Using a potentiometer wire whose emf is lower than the cell being measured.
Definitions
- Term
Wheatstone Bridge, Meter Bridge and Potentiometer
- Meaning
A Wheatstone bridge is balanced when P/Q = R/S; a potentiometer compares potential differences without drawing current at balance.
- Term
Wheatstone Bridge, Meter Bridge and Potentiometer — explanation
- Meaning
Null methods are accurate precisely because at balance no current flows through the detector, so the internal resistance of the source and the galvanometer stop mattering.
Learning objectives
Apply the balance condition to determine an unknown resistance.
Evaluate why null methods are more accurate than direct measurement.
Formulae
- Key point
Balance condition: P/Q = R/S; the galvanometer reads zero.
- Key point
Potentiometer measures emf without drawing current, unlike a voltmeter.
- Key point
Potential gradient k = V/L along the wire.
Prerequisites
PHY-U5-CUR-T1-S1-C2
Common mistakes
Using a potentiometer wire whose emf is lower than the cell being measured.
Assuming a bridge can be balanced for any set of resistances.
Keywords
Wheatstone
Bridge
Meter
Bridge
Potentiometer
Practice preview
What is the condition for a Wheatstone bridge to be balanced?…
easy
Why is a potentiometer preferred over a voltmeter for measuring the EMF of a cell?…
easy
In a Wheatstone bridge, the four arms have resistances P = 10 Ohm, Q = 20 Ohm, R = 30 Ohm, and S = 40 Ohm. If a 6.2 V battery is connected across the bridge, what is the current flowing through the galvanometer of resist…
hard