DC motors worksheet with answers

Free printable DC motors worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

New worksheetPractise online with hints

For teachers: free to print, copy and use in class. Every new worksheet has new values and its own answer key. A link to ExamProblems on your course page is appreciated.

Name: ____________________   Date: ____________

1.Easy
+−120 VRa​M+−E = 116 Vn = 1200 rpmT

A DC motor turns at 1200 rpm, and its back-EMF at that speed is 116 V. Find the motor constant k in V·s/rad.

E = 116 Vn = 1200 rpm
k = V·s/rad
2.Easy
+−240 VRa​ = 1 ΩIa​ = 25 AM+−EωT

A DC motor runs from 240 V with an armature current of 25 A. The armature resistance is 1 Ω. Find the developed (electromagnetic) power Pdev.

V = 240 VIa = 25 ARa = 1 Ω
Pdev = W
3.Medium
+−VRa​M+−En = 3000 rpmT = ?

A DC motor delivers 1 kW of mechanical power at 3000 rpm. Find the shaft torque T.

P = 1 kWn = 3000 rpm
T = N·m
4.Medium
T (N·m)n (rpm)n0​ = ?

A DC motor with k = 0.3 V·s/rad runs from 120 V. Neglecting all losses at no load, find its no-load speed n0 in rpm.

V = 120 Vk = 0.3 V·s/rad
n0 = rpm
5.Hard
+−240 VRs​ = ?Ra​ = 1.2 ΩM+−En = 800 rpmT = 12 N·m

A DC motor (k = 0.8 V·s/rad, Ra = 1.2 Ω) on a fixed 240 V supply drives a load of 12 N·m. Find the series resistance Rs that slows it down to 800 rpm.

V = 240 Vk = 0.8 V·s/radRa = 1.2 ΩT = 12 N·mn = 800 rpm
Rs = Ω
6.Hard
T (N·m)n (rpm)0.72 N·m600 rpm

A DC motor with k = 0.12 V·s/rad and Ra = 0.4 Ω must drive a load of 0.72 N·m at 600 rpm. Find the armature voltage V it needs.

k = 0.12 V·s/radRa = 0.4 ΩT = 0.72 N·mn = 600 rpm
V = V

Answer key

  1. 1. k = 0.9231 V·s/rad
  2. 2. Pdev = 5375 W
  3. 3. T = 3.183 N·m
  4. 4. n0 = 3820 rpm
  5. 5. Rs = 10.33 Ω
  6. 6. V = 9.94 V

Full step-by-step solutions: practise this topic on examproblems.com.