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
+−240 VRa​ = 0.4 ΩIa​ = ?M+−E = 228 VωT

A DC motor on a 240 V supply has an armature resistance of 0.4 Ω. At its present speed the back-EMF is 228 V. Find the armature current Ia.

V = 240 VE = 228 VRa = 0.4 Ω
Ia = A
2.Easy
+−220 VRa​ = 0.8 ΩIa​ = ?M+−E = 212 VωT

A DC motor on a 220 V supply has an armature resistance of 0.8 Ω. At its present speed the back-EMF is 212 V. Find the armature current Ia.

V = 220 VE = 212 VRa = 0.8 Ω
Ia = A
3.Medium
T (N·m)n (rpm)Tst​ = ?n0​

A DC motor with k = 1.2 N·m/A and Ra = 1.5 Ω is connected to 120 V. Find its stall torque Tstall, the torque at zero speed.

V = 120 Vk = 1.2 N·m/ARa = 1.5 Ω
Tstall = N·m
4.Medium
+−VRa​M+−En = 1200 rpmT = ?

A DC motor delivers 5.5 kW of mechanical power at 1200 rpm. Find the shaft torque T.

P = 5.5 kWn = 1200 rpm
T = N·m
5.Hard
+−48 VRa​ = 2.5 ΩM+−EωT

A small DC motor has an armature resistance of 2.5 Ω and runs from 48 V. Neglecting rotational losses, find the largest mechanical power Pmax it can develop at any speed.

V = 48 VRa = 2.5 Ω
Pmax = W
6.Hard
+−48 VRa​ = 0.8 ΩM+−EωT

A small DC motor has an armature resistance of 0.8 Ω and runs from 48 V. Neglecting rotational losses, find the largest mechanical power Pmax it can develop at any speed.

V = 48 VRa = 0.8 Ω
Pmax = W

Answer key

  1. 1. Ia = 30 A
  2. 2. Ia = 10 A
  3. 3. Tstall = 96 N·m
  4. 4. T = 43.77 N·m
  5. 5. Pmax = 230.4 W
  6. 6. Pmax = 720 W

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