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Assertion (A): Armature resistance control method of speed control of dc motors is wasteful and inefficient.
Reason (R): Large amount of power is wasted in the control resistances, specially in case of shunt motors'.
  • a)
    Both A and R are true and R is a correct explanation of A.
  • b)
    Both A and R are true but R is not a correct explanation of A.
  • c)
    A is true but R is false.
  • d)
    A is false but R is true.
Correct answer is option 'A'. Can you explain this answer?
Most Upvoted Answer
Assertion (A): Armature resistance control method of speed control of ...
Assertion (A): Armature resistance control method of speed control of DC motors is wasteful and inefficient.

Reason (R): Large amount of power is wasted in the control resistances, specially in case of shunt motors.

Explanation:

The given assertion and reason state that the armature resistance control method of speed control of DC motors is wasteful and inefficient because a large amount of power is wasted in the control resistances, especially in the case of shunt motors. Let's analyze this statement in detail.

Armature Resistance Control Method:
In the armature resistance control method, the speed of a DC motor is controlled by varying the armature resistance. This is achieved by inserting a variable resistance in series with the armature winding. By changing the resistance, the voltage drop across the armature winding is varied, which in turn affects the motor speed.

Power Loss in Control Resistances:
The control resistances used in the armature resistance control method cause a significant power loss. This power loss happens due to the voltage drop across the resistance and the current flowing through it. The power loss can be calculated using the formula: Power Loss = Voltage Drop * Current.

Shunt Motors:
Shunt motors are a type of DC motors where the field winding is connected in parallel (shunt) with the armature winding. In shunt motors, the armature resistance control method is commonly used for speed control.

Explanation of Assertion and Reason:
The assertion states that the armature resistance control method is wasteful and inefficient. This is because a large amount of power is wasted in the control resistances. The reason provided further explains that this wastage of power is particularly significant in the case of shunt motors.

The armature resistance control method causes power loss due to the voltage drop across the control resistances. This power loss is undesirable as it reduces the overall efficiency of the motor and leads to wastage of energy. In the case of shunt motors, where the armature resistance control method is commonly used, the power loss can be even higher.

Conclusion:
Based on the above explanation, both the assertion and reason are true, and the reason correctly explains the assertion. The armature resistance control method of speed control of DC motors is indeed wasteful and inefficient due to the power loss in the control resistances, especially in the case of shunt motors.
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Assertion (A): Armature resistance control method of speed control of dc motors is wasteful and inefficient.Reason (R): Large amount of power is wasted in the control resistances, specially in case of shunt motors.a)Both A and R are true and R is a correct explanation of A.b)Both A and R are true but R is not a correct explanation of A.c)A is true but R is false.d)A is false but R is true.Correct answer is option 'A'. Can you explain this answer?
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