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

R = 50 Ωl = 20 cmL = 100 cm

R_x = Ω

2.Easy

The bridge shown is supplied with V_s = 6 V and its output is open. Find the current I_s drawn from the supply, in mA.

V_s = 6 VR₁ = 1000 ΩR₂ = 200 ΩR₃ = 10 ΩR₄ = 40 Ω

I_s = mA

3.Medium

A galvanometer with a resistance of 500 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 = 250 ΩR₂ = 300 ΩR₃ = 500 ΩR₄ = 250 ΩR_g = 500 Ω

I_g = µA

4.Medium

A bridge with four 300 Ω arms is supplied with 3 V. When the sensor R₂ changes, the output reads V_ab = 29.41 mV. Find the exact change ΔR of R₂.

V_s = 3 VR = 300 ΩV_ab = 29.41 mV

ΔR = Ω

5.Hard

A strain gauge (GF = 2.1) on a member with E = 110 GPa forms a quarter bridge excited with 10 V. The output reads 6.3 mV. Find the axial stress σ in MPa.

V_s = 10 VGF = 2.1V_o = 6.3 mVE = 110 GPa

σ = MPa

6.Hard

A 120 Ω strain gauge with gauge factor 2 is bonded to a steel bar. Under load its resistance rises by 0.12 Ω. Find the strain ε in microstrain (µε).

R = 120 ΩGF = 2ΔR = 0.12 Ω

ε = µε

Answer key

1. R_x = 200 Ω
2. I_s = 125 mA
3. I_g = 792.5 µA
4. ΔR = 12 Ω
5. σ = 132 MPa
6. ε = 500 µε

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