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

In a slide-wire (metre) bridge a known 50 Ω resistor sits in the left gap and an unknown resistor Rₓ in the right gap. The galvanometer reads zero when the jockey is 25 cm from the left end A of the 100 cm wire. Find R_x.

R = 50 Ωl = 25 cmL = 100 cm

R_x = Ω

2.Easy

The Wheatstone bridge in the diagram is balanced by adjusting R₃. R₁ = 1000 Ω, R₂ = 200 Ω and R₄ = 120 Ω. Find the setting R₃.

R₁ = 1000 ΩR₂ = 200 ΩR₄ = 120 Ω

R₃ = Ω

3.Medium

A 400 Ω strain gauge is one arm (R₂) of a bridge with four equal 400 Ω arms and an excitation of 5 V. Find the power P_g dissipated in the gauge, in mW. Self-heating limits the excitation.

V_s = 5 VR = 400 Ω

P_g = mW

4.Medium

A galvanometer with a resistance of 20 Ω is connected between a and b of the bridge shown (V_s = 9 V). Find the galvanometer current I_g from a to b, in µA.

V_s = 9 VR₁ = 250 ΩR₂ = 250 ΩR₃ = 150 ΩR₄ = 80 ΩR_g = 20 Ω

I_g = µA

5.Hard

A strain gauge (GF = 2) on a member with E = 210 GPa forms a quarter bridge excited with 10 V. The output reads 2.5 mV. Find the axial stress σ in MPa.

V_s = 10 VGF = 2V_o = 2.5 mVE = 210 GPa

σ = MPa

6.Hard

A 350 Ω strain gauge with gauge factor 2 is bonded to a steel bar. Under load its resistance rises by 0.42 Ω. Find the strain ε in microstrain (µε).

R = 350 ΩGF = 2ΔR = 0.42 Ω

ε = µε

Answer key

1. R_x = 150 Ω
2. R₃ = 600 Ω
3. P_g = 15.63 mW
4. I_g = 6946 µA
5. σ = 105 MPa
6. ε = 600 µε

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