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 35 cm from the left end A of the 100 cm wire. Find R_x.

R = 50 Ωl = 35 cmL = 100 cm

R_x = Ω

2.Easy

In the bridge shown, V_s = 10 V, R₁ = 10 Ω and R₂ = 40 Ω. Find the voltage V_a of node a with respect to the negative supply rail.

V_s = 10 VR₁ = 10 ΩR₂ = 40 ΩR₃ = 10 ΩR₄ = 200 Ω

V_a = V

3.Medium

Find the Thévenin resistance R_th of the bridge shown, seen from the output terminals a and b.

V_s = 10 VR₁ = 40 ΩR₂ = 400 ΩR₃ = 800 ΩR₄ = 600 Ω

R_th = Ω

4.Medium

A galvanometer with a resistance of 50 Ω is connected between a and b of the bridge shown (V_s = 2 V). Find the galvanometer current I_g from a to b, in µA.

V_s = 2 VR₁ = 100 ΩR₂ = 100 ΩR₃ = 500 ΩR₄ = 800 ΩR_g = 50 Ω

I_g = µA

5.Hard

A bridge with 120 Ω arms is excited with 10 V and has one active gauge (quarter bridge). The gauge factor is 2 and the strain is 500 µε. Find the bridge output V_o in mV.

V_s = 10 VGF = 2ε = 500 µε

V_o = mV

6.Hard

A strain gauge (GF = 2) on a member with E = 200 GPa forms a quarter bridge excited with 2.5 V. The output reads 0.625 mV. Find the axial stress σ in MPa.

V_s = 2.5 VGF = 2V_o = 0.625 mVE = 200 GPa

σ = MPa

Answer key

1. R_x = 92.86 Ω
2. V_a = 8 V
3. R_th = 379.2 Ω
4. I_g = −566 µA
5. V_o = 2.5 mV
6. σ = 100 MPa

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