### DC Motors Objectives Part 01

**01 .** The fully load current of a 20HP 500V Dc motor will be closer to **35A**

**02 . ** The speed of a dc motor may be varied by varying** (a)field current (b)applied voltage (c)resistance in series with armature(d) any of above**

**03 .** In dc motor, the conditions for maximum power is **Back emf=1/2(supply voltage)**

**04 . ** If conditions for maximum power for a dc motor are established, the efficiency of motor will be** less than 50%**

**05 .** A 200 V dc machine has an armature resistance of 0.5 ohm. If the full Armature current is 30A, the induced emf when machine acts as

a) generator (b) motor will be **120V,210V**

**06 . ** The speed of a dc motor is **directly proportional to back emf.**

**07 .** The ratio of starting torque to fully load torque is least in case of** shunt motors**

**08 . ** Which of the following is not necessarily the advantage of dc motors over ac motors **Low Cost**

**09 .** Which motor will have least percentage increase of input current for the same percentage increase in torque **series motor.**

**10 . ** The mechanical power developed by a dc motor is maximum when the ratio of back emf/applied voltage is** 0.5**

**11 . ** The speed of a series-wound dc motor** increases as flux decreases**

**12 . **Following controls play significant role in the speed control of dc motors**a) Control of flux (b) armature resistance control (c)supply voltage control**

**13 .** The speed regulation of a dc motor is** (No load speed-full** **load speed)/Full load speed**

**14 .** A dc motor having full load speed of 800 and speed regulation of 8% will have no load speed of **864 rpm.**

**15 . ** For a series motor if Ta be the torque and Ia the armature current, then

which relation is valid for the conditions before saturation Ta ∞** Ia2.**

**16 .** In the dc series motor, shaft torque is less than the armature torque due to**Stray losses.**

**17 . ** Dc motor with self-loading properties is** differentially compound motor.**

**18 . ** The current drawn by a 120V dc motor of armature resistance 0.4 ohm and back emf 112V is **20A.**

**19 . ** If the load current and flux of a dc motor are held constant and voltage applied across its armature is increased by 5 percent, the speed of motor will be **increase by about 5%**

**20 . ** A dc motor develops a torque of 140N-m at 1400 rpm. If the motor now runs at 1000rpm, the torque developed will be **140 N-m**