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

R = 5 Ωl = 30 cmL = 100 cm

R_x = Ω

2.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 40 cm from the left end A of the 100 cm wire. Find R_x.

R = 5 Ωl = 40 cmL = 100 cm

R_x = Ω

3.Medium

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

V_s = 15 VR₁ = 600 ΩR₂ = 80 ΩR₃ = 250 ΩR₄ = 400 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 = 3 V). Find the galvanometer current I_g from a to b, in µA.

V_s = 3 VR₁ = 60 ΩR₂ = 100 ΩR₃ = 120 ΩR₄ = 300 ΩR_g = 50 Ω

I_g = µA

5.Hard

A load cell (a full bridge of strain gauges) has a rated output of 2.5 mV/V at its rated load of 100 kg. It is excited with 10 V. Find its output V_o under a load of 75 kg.

2.5 mV/VF_rated = 100 kgV_s = 10 VF = 75 kg

V_o = mV

6.Hard

A 120 Ω strain gauge with gauge factor 2.05 is bonded to a steel bar. Under load its resistance rises by 0.2952 Ω. Find the strain ε in microstrain (µε).

R = 120 ΩGF = 2.05ΔR = 0.2952 Ω

ε = µε

Answer key

1. R_x = 11.67 Ω
2. R_x = 7.5 Ω
3. R_th = 224.4 Ω
4. I_g = −1546 µA
5. V_o = 18.75 mV
6. ε = 1200 µε

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