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

The bridge shown is supplied with V_s = 5 V and its output is open. Find the current I_s drawn from the supply, in mA.

V_s = 5 VR₁ = 300 ΩR₂ = 400 ΩR₃ = 120 ΩR₄ = 120 Ω

I_s = mA

2.Easy

The Wheatstone bridge in the diagram is balanced: the galvanometer reads zero. R₁ = 20 Ω, R₂ = 250 Ω and R₃ = 120 Ω. Find the unknown resistor R₄.

R₁ = 20 ΩR₂ = 250 ΩR₃ = 120 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 = 15 VR₁ = 80 ΩR₂ = 500 ΩR₃ = 250 ΩR₄ = 10 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 = 2 V). Find the galvanometer current I_g from a to b, in µA.

V_s = 2 VR₁ = 400 ΩR₂ = 120 ΩR₃ = 1000 ΩR₄ = 20 ΩR_g = 50 Ω

I_g = µA

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 50 kg. It is excited with 12 V. Find its output V_o under a load of 10 kg.

1.5 mV/VF_rated = 50 kgV_s = 12 VF = 10 kg

V_o = mV

6.Hard

A quarter bridge (one active gauge, GF = 2.12) is excited with 5 V. The largest strain to be measured is 1200 µε, and it must give 5 V at the input of an analogue-to-digital converter. Find the amplifier gain G.

V_s = 5 VGF = 2.12ε_max = 1200 µεV_FS = 5 V

G =

Answer key

1. I_s = 27.98 mA
2. R₄ = 1500 Ω
3. R_th = 78.58 Ω
4. I_g = 2608 µA
5. V_o = 3.6 mV
6. G = 1572

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