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

R = 100 Ωl = 70 cmL = 100 cm

R_x = Ω

2.Easy

The bridge shown is supplied with V_s = 3 V and its output is open. Find the current I_s drawn from the supply, in mA.

V_s = 3 VR₁ = 50 ΩR₂ = 200 ΩR₃ = 60 ΩR₄ = 600 Ω

I_s = mA

3.Medium

A 350 Ω strain gauge is one arm (R₂) of a bridge with four equal 350 Ω arms and an excitation of 5 V. Find the power P_g dissipated in the gauge, in mW. Self-heating limits the excitation.

V_s = 5 VR = 350 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 = 2 VR₁ = 120 ΩR₂ = 10 ΩR₃ = 300 ΩR₄ = 10 Ω

R_th = Ω

5.Hard

A bridge with 350 Ω arms is excited with 5 V and has four active gauges, two in tension and two in compression (full bridge). The gauge factor is 2.1 and the strain is 750 µε. Find the bridge output V_o in mV.

V_s = 5 VGF = 2.1ε = 750 µε

V_o = mV

6.Hard

A quarter bridge (one active gauge, GF = 2.05) is excited with 5 V. The largest strain to be measured is 750 µε, and it must give 10 V at the input of an analogue-to-digital converter. Find the amplifier gain G.

V_s = 5 VGF = 2.05ε_max = 750 µεV_FS = 10 V

G =

Answer key

1. R_x = 42.86 Ω
2. I_s = 16.55 mA
3. P_g = 17.86 mW
4. R_th = 18.91 Ω
5. V_o = 7.875 mV
6. G = 5203

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