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 100 Ω resistor sits in the left gap and an unknown resistor Rₓ in the right gap. The galvanometer reads zero when the jockey is 45 cm from the left end A of the 100 cm wire. Find R_x.

R = 100 Ωl = 45 cmL = 100 cm

R_x = Ω

2.Easy

The Wheatstone bridge in the diagram is balanced: the galvanometer reads zero. R₁ = 20 Ω, R₂ = 300 Ω and R₃ = 40 Ω. Find the unknown resistor R₄.

R₁ = 20 ΩR₂ = 300 ΩR₃ = 40 Ω

R₄ = Ω

3.Medium

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

V_s = 9 VR₁ = 60 ΩR₂ = 1000 ΩR₃ = 120 ΩR₄ = 40 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 = 9 V). Find the galvanometer current I_g from a to b, in µA.

V_s = 9 VR₁ = 300 ΩR₂ = 120 ΩR₃ = 500 ΩR₄ = 250 ΩR_g = 50 Ω

I_g = µA

5.Hard

A bridge with 350 Ω arms is excited with 3 V and has four active gauges, two in tension and two in compression (full bridge). The gauge factor is 2.12 and the strain is 1200 µε. Find the bridge output V_o in mV.

V_s = 3 VGF = 2.12ε = 1200 µε

V_o = mV

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 and the strain is 250 µε. Find the bridge output V_o in mV.

V_s = 5 VGF = 2ε = 250 µε

V_o = mV

Answer key

1. R_x = 122.2 Ω
2. R₄ = 600 Ω
3. R_th = 86.6 Ω
4. I_g = −1417 µA
5. V_o = 7.632 mV
6. V_o = 0.625 mV

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