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 5 Ω resistor sits in the left gap and an unknown resistor Rₓ in the right gap. The galvanometer reads zero when the jockey is 70 cm from the left end A of the 100 cm wire. Find R_x.

R = 5 Ωl = 70 cmL = 100 cm

R_x = Ω

2.Easy

In the bridge shown, V_s = 9 V, R₁ = 400 Ω and R₂ = 250 Ω. Find the voltage V_a of node a with respect to the negative supply rail.

V_s = 9 VR₁ = 400 ΩR₂ = 250 ΩR₃ = 80 ΩR₄ = 1000 Ω

V_a = V

3.Medium

A 100 Ω strain gauge is one arm (R₂) of a bridge with four equal 100 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 = 100 Ω

P_g = mW

4.Medium

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

V_s = 9 VR₁ = 10 ΩR₂ = 1000 ΩR₃ = 10 ΩR₄ = 20 Ω

R_th = Ω

5.Hard

A strain gauge (GF = 2.05) on a member with E = 70 GPa forms a quarter bridge excited with 3 V. The output reads 0.384 mV. Find the axial stress σ in MPa.

V_s = 3 VGF = 2.05V_o = 0.384 mVE = 70 GPa

σ = MPa

6.Hard

A bridge with 350 Ω arms is excited with 5 V and has one active gauge (quarter bridge). The gauge factor is 2.05 and the strain is 400 µε. Find the bridge output V_o in mV.

V_s = 5 VGF = 2.05ε = 400 µε

V_o = mV

Answer key

1. R_x = 2.143 Ω
2. V_a = 3.462 V
3. P_g = 90 mW
4. R_th = 16.57 Ω
5. σ = 17.48 MPa
6. V_o = 1.025 mV

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