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 20 Ω resistor sits in the left gap and an unknown resistor Rₓ in the right gap. The galvanometer reads zero when the jockey is 25 cm from the left end A of the 100 cm wire. Find R_x.

R = 20 Ωl = 25 cmL = 100 cm

R_x = Ω

2.Easy

In the bridge shown, V_s = 2 V, R₁ = 40 Ω and R₂ = 50 Ω. Find the voltage V_a of node a with respect to the negative supply rail.

V_s = 2 VR₁ = 40 ΩR₂ = 50 ΩR₃ = 40 ΩR₄ = 800 Ω

V_a = V

3.Medium

A galvanometer with a resistance of 100 Ω is connected between a and b of the bridge shown (V_s = 5 V). Find the galvanometer current I_g from a to b, in µA.

V_s = 5 VR₁ = 150 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 = 2 VR₁ = 10 ΩR₂ = 40 ΩR₃ = 600 ΩR₄ = 50 Ω

R_th = Ω

5.Hard

A 120 Ω strain gauge with gauge factor 2 is bonded to a steel bar. Under load its resistance rises by 0.048 Ω. Find the strain ε in microstrain (µε).

R = 120 ΩGF = 2ΔR = 0.048 Ω

ε = µε

6.Hard

A quarter bridge (one active gauge, GF = 2.1) is excited with 2.5 V. The largest strain to be measured is 1200 µε, and it must give 2.5 V at the input of an analogue-to-digital converter. Find the amplifier gain G.

V_s = 2.5 VGF = 2.1ε_max = 1200 µεV_FS = 2.5 V

G =

Answer key

1. R_x = 60 Ω
2. V_a = 1.111 V
3. I_g = 1923 µA
4. R_th = 54.15 Ω
5. ε = 200 µε
6. G = 1587

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