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 10 Ω resistor sits in the left gap and an unknown resistor Rₓ in the right gap. The galvanometer reads zero when the jockey is 80 cm from the left end A of the 100 cm wire. Find R_x.

R = 10 Ωl = 80 cmL = 100 cm

R_x = Ω

2.Easy

The Wheatstone bridge in the diagram is balanced: the galvanometer reads zero. R₁ = 40 Ω, R₂ = 100 Ω and R₃ = 1000 Ω. Find the unknown resistor R₄.

R₁ = 40 ΩR₂ = 100 ΩR₃ = 1000 Ω

R₄ = Ω

3.Medium

A galvanometer with a resistance of 100 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 = 120 ΩR₂ = 60 ΩR₃ = 400 ΩR₄ = 100 ΩR_g = 100 Ω

I_g = µA

4.Medium

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

V_s = 10 VR₁ = 20 ΩR₂ = 250 ΩR₃ = 40 ΩR₄ = 20 Ω

R_th = Ω

5.Hard

A load cell (a full bridge of strain gauges) has a rated output of 1.5 mV/V at its rated load of 100 kg. It is excited with 5 V. Find its output V_o under a load of 25 kg.

1.5 mV/VF_rated = 100 kgV_s = 5 VF = 25 kg

V_o = mV

6.Hard

A quarter bridge (one active gauge, GF = 2.05) is excited with 3 V. The largest strain to be measured is 500 µε, and it must give 3.3 V at the input of an analogue-to-digital converter. Find the amplifier gain G.

V_s = 3 VGF = 2.05ε_max = 500 µεV_FS = 3.3 V

G =

Answer key

1. R_x = 2.5 Ω
2. R₄ = 2500 Ω
3. I_g = 5455 µA
4. R_th = 31.85 Ω
5. V_o = 1.875 mV
6. G = 4293

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