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
+−48 VRa​ = 0.5 ΩIa​ = 4 AM+−En = ?T

A DC motor with k = 0.12 V·s/rad and an armature resistance of 0.5 Ω runs from 48 V and draws 4 A. Find its speed n in rpm.

V = 48 VRa = 0.5 ΩIa = 4 Ak = 0.12 V·s/rad
n = rpm
2.Easy
+−240 VRa​ = 1.2 ΩIa​ = 25 AM+−E = ?ωT

A DC motor runs from a 240 V supply and draws an armature current of 25 A. Its armature resistance is 1.2 Ω. Find the back-EMF E.

V = 240 VIa = 25 ARa = 1.2 Ω
E = V
3.Medium
+−VRa​M+−En = 1800 rpmT = ?

A DC motor delivers 2.2 kW of mechanical power at 1800 rpm. Find the shaft torque T.

P = 2.2 kWn = 1800 rpm
T = N·m
4.Medium
+−VRa​M+−En = 750 rpmT = ?

A DC motor delivers 1 kW of mechanical power at 750 rpm. Find the shaft torque T.

P = 1 kWn = 750 rpm
T = N·m
5.Hard
T (N·m)n (rpm)0.8 N·m600 rpm

A DC motor with k = 0.08 V·s/rad and Ra = 0.2 Ω must drive a load of 0.8 N·m at 600 rpm. Find the armature voltage V it needs.

k = 0.08 V·s/radRa = 0.2 ΩT = 0.8 N·mn = 600 rpm
V = V
6.Hard
+−240 VRa​ = 2 ΩIa​: 15 → 6 AM+−En = ?T

A separately excited DC motor on 240 V (Ra = 2 Ω) runs at 1200 rpm with an armature current of 15 A. The load changes and the current becomes 6 A, with the field unchanged. Find the new speed n2.

V = 240 VRa = 2 Ωn1 = 1200 rpmIa1 = 15 AIa2 = 6 A
n2 = rpm

Answer key

  1. 1. n = 3661 rpm
  2. 2. E = 210 V
  3. 3. T = 11.67 N·m
  4. 4. T = 12.73 N·m
  5. 5. V = 7.027 V
  6. 6. n2 = 1303 rpm

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