The current drawn by the armature of D.C. motor is directly proportional to

If A varies directly proportional to C and B also varies directly proportional to C, which one of the following is not correct ?

A

$$\left( {A + B} \right)\alpha \,C$$

B

$$\left( {A - B} \right)\alpha \,\frac{1}{C}$$

C

$$\sqrt {AB} \,\alpha \,C$$

D

$$\frac{A}{B} = {\text{constant}}$$

A synchronous motor is running with normal excitation. When the load is increased, the armature current drawn by it increases because

A

Speed of the motor is reduced

B

Power factor is decreased

C

Eb (back e.m.f.) becomes less than V (applied voltage)

D

Er (net resultant voltage) in armature is increased

As the load is applied to a synchronous motor, the motor takes more armature current because

A

The increased load has to take more current

B

The rotor by shifting its phase backward causes motor to take more current

C

The back e.m.f. decreases causing an increase in motor current

D

The rotor strengthens the rotating field causing more motor current

The armature torque of the D.C. shunt motor is proportional to

A

field flux only

B

armature current only

C

both (A) and (B)

D

none of the above

As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit

A

A resistance is connected in series with armature

B

A resistance is connected parallel to the armature

C

Armature is temporarily open circuited

D

A high value resistor is connected across the field winding

In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be

A

Almost negligible

B

Rated full-load current

C

Less than full-load current

D

More than full-load current

When load on an over-excited or under excited synchronous motor is increased, rate of change of its armature current as compared with that of power factor is

A

more

B

less

C

equal

D

twice

The armature current of the synchronous motor has higher values for

A

high excitation only

B

low excitation only

C

both (A) and (B)

D

none of the above

In a synchronous motor, the armature current has large values for

A

high excitation only

B

low excitation only

C

both high and low excitation

D

none of the above

The armature current of the synchronous motor

A

has large values for low excitation i niy

B

has large values for high excitation only

C

has large values for low and high excitation

D

any of the above

The current drawn by the armature of D.C. motor is directly proportional to

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