# PHYSICS: D.C. MACHINE 04/08 Online Test

A 250 V, D.C shunt generator has a voltage regulation of 8%. The voltage at no-load will be
230 volts
250 volts
258 volts
270 volts
In which of the following tests on D.C machines minimum number of two machines are required
Brake test
Retardation test
Back to back test
Swinburne's test
Hopkinson's test is conducted at
The load current of a D.C series motor is 50 A, when supplying a full load torque. If the current reduced to 25 A, the torque will be
What is the function of commutator of the D.C motor?
To reduce friction
To convert A.C into D.C
To convert D.C into A.C
To feed the current to the armature
Which of the following loads normally start at rated torque?
Cranes
Centrifugal pumps
Industrial blowers
Conveyors and printing presses
A punching machine, having intermittent light and heavy loads, should have
Shunt motor
Series motor
Differentially compound motor
Cumulatively compound motor
The flux set up by the armature current has
Magnetizing effect
Cross magnetizing effect
Demagnetizing effect
(2) And (3) both.
The voltage between commutator segments should not exceed than
2 volts
15 volts
50 volts
200 volts
In Hopkinson's test for D.C motors
Speeds of the motors are separately controlled
Both motors are run as generators
Both machines are mechanically coupled
Both motors run at their respective rated speeds
In Ward Leonard control change in speed of motor can be obtained by varying
Supply voltage of the d.c. motor
Tieldexcitation of D.C motor
Annature voltage of D.C motor
Annature current of D.C motor
On increasing the load on D.C series generator its terminal voltage will'
Increase
Decrease slightly
Decrease sharply
Remain same
Full load speed of a D.C motor being 1000 r.p.m., and speed regulation being 90%, no load speed will be
900 r.p.m.
1000 r.p.m.
1110 r.p.m
1200 r.p.m
Yoke of a D.C generator is made of
Wood
Copper
Cast iron
Aluminum
In a D.C shunt motor, running at light load, if the field winding gets opened, what will happen?
Motor will stop instantly
Motor will take heavy input current
Motor will make mechanical noise
Motor will tend to pick up high speed
A d.c series motor
Always runs at constant speed
Should always be started on load
May stop if the field gets opened
Is not suitable for high starting torque
Conventional exciter of a turbo generator is basically a
Series generator
Shunt-generator
Compound generator of
Separately excited generator
Full load terminal voltage in a level compounded d.c. Generator is
Less than no load terminal voltage
More than no load terminal voltage
Negligibly low
For a given torque, reduction of the field turns of a D.C series motor
Increases its speed but armature current remains the same
Decreases its speed, armature current remains the same
Decreases its speed, demanding less armature current
Increases its speed, demanding more armatures current
The speed current characteristic of a D.C series motor is
Straight line, starting from origin
Straight line, not starting from origin
Rectangular hyperbola in shape
None of the above
Description:

This is test is a part of a series of eight test which helps students to check the level of knowledge in Electricity, specifically in the DC Machine in Physics.

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