The Wheatstone bridge is a circuit invented in 1833 by Samuel Hunter Christie to measure an unknown electrical resistance. It uses a galvanometer to monitor a balanced state where no current flows through the galvanometer (ig=0). By adjusting variable resistors to reach this balanced state, the mathematical ratio of the arms can be used to calculate the fourth unknown resistance. The Wheatstone bridge found many applications in measuring strain, locating breaks in power lines, and indirectly measuring other variables that impact electrical resistance, such as temperature, force, and pressure.

1. WHEATSTONE BRIDGE
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2. History
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 The Wheatstone Bridge was invented in 1833 by
Samuel Hunter Christie
 Later named after Sir Charles Wheatstone for his
many applications of the circuit through the 1840s
 The most common procedure for the bridge remains
the testing of unknown electrical resistance

3. Wheatstone Bridge
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4. Analysis
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 Identify the currents

5. Consider the bridge at “balance”, ig=0
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1 3
2
3 3
1 1 2 2
x
x x
i i
i i
i R i R
i R i R




g
g
g

6. Some Algebra
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1 3 2
1 1 2 2
3
1 2
2
3
1
x
x
x
i R i R
i R i R
R R
R R
R
R R
R





7. Use to Measure Resistance
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3
1
x
R
R R
R

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Ratio Arms

8. Working
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 By changing resistors to adjusting variable resistors
to balance the device, the mathematical ratio is used
to calculate the fourth (unknown) resistance

9. Applications
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 Main focus of the Wheatstone Bridge = applications
using electricity
 The circuit monitors sensor devices like strain
gauges – it reads the level of the strain in the system
 The galvanometer measures whether the gauges
are balanced or not
 Electrical power distributors use the Wheatstone
Bridge to locate breaks in the power lines

10. Impact of the Wheatstone Bridge
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 The Wheatstone Bridge is a very simple design,
although there are more complex versions of
achieving the same outcome
 Can be adjusted easily
 Fairly inexpensive to produce
 Also indirectly measures any variable that would
change the resistance of a material
 Ex: temperature, force, pressure

11. THANK YOU
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