Wheatstone bridge & strain gauges worksheet with answers

Free printable Wheatstone bridge & strain gauges worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy

The Wheatstone bridge in the diagram is balanced: the galvanometer reads zero. R₁ = 120 Ω, R₂ = 50 Ω and R₃ = 300 Ω. Find the unknown resistor R₄.

R₁ = 120 ΩR₂ = 50 ΩR₃ = 300 Ω

R₄ = Ω

2.Easy

The Wheatstone bridge in the diagram is balanced by adjusting R₃. R₁ = 120 Ω, R₂ = 400 Ω and R₄ = 600 Ω. Find the setting R₃.

R₁ = 120 ΩR₂ = 400 ΩR₄ = 600 Ω

R₃ = Ω

3.Medium

A galvanometer with a resistance of 100 Ω is connected between a and b of the bridge shown (V_s = 3 V). Find the galvanometer current I_g from a to b, in µA.

V_s = 3 VR₁ = 50 ΩR₂ = 10 ΩR₃ = 300 ΩR₄ = 400 ΩR_g = 100 Ω

I_g = µA

4.Medium

A 150 Ω strain gauge is one arm (R₂) of a bridge with four equal 150 Ω arms and an excitation of 6 V. Find the power P_g dissipated in the gauge, in mW. Self-heating limits the excitation.

V_s = 6 VR = 150 Ω

P_g = mW

5.Hard

A load cell (a full bridge of strain gauges) has a rated output of 1.5 mV/V at its rated load of 500 kg. It is excited with 10 V. Find its output V_o under a load of 125 kg.

1.5 mV/VF_rated = 500 kgV_s = 10 VF = 125 kg

V_o = mV

6.Hard

A quarter bridge (one active gauge, GF = 2.1) is excited with 3 V. The largest strain to be measured is 800 µε, and it must give 3.3 V at the input of an analogue-to-digital converter. Find the amplifier gain G.

V_s = 3 VGF = 2.1ε_max = 800 µεV_FS = 3.3 V

G =

Answer key

1. R₄ = 125 Ω
2. R₃ = 180 Ω
3. I_g = −4340 µA
4. P_g = 60 mW
5. V_o = 3.75 mV
6. G = 2619

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