Dynamometer Type Wattmeter MCQ || Dynamometer Type Wattmeter Questions and Answers

1. A dynamometer wattmeter is almost universally used for the measurement of  _______

  1. AC Power Only
  2. DC Power Only
  3. Both AC and DC Power
  4. Frequency

Answer.3. Both AC and DC Power

Explanation:

A dynamometer wattmeter is almost universally used for the measurement of d.c. as well as a.c. power. It works on the dynamometer principle i.e. mechanical force exists between two current-carrying conductors or coils.

 

2.  In A.C. circuits, power consumed is ________

  1. Product of voltage and current
  2. It depends on the p.f. of the circuit in addition to voltage and current
  3. It depends on the supply voltage
  4. It depends on the magnitude of the circuit current

Answer.2. It depends on the p.f. of the circuit in addition to voltage and current

Explanation:

Power developed in an ac circuit can be expressed as P=VI cos ∅.

where

V is the voltage across the circuit

I is the current flowing through the circuit

cos∅ is the power factor of the circuit.

Hence in AC circuit power consumed depends on the p.f. of the circuit in addition to voltage and current.

 

3. When the moving coil in a Dynamometer type wattmeter deflects ________

  1. Pointer moves
  2. Pointer doesn’t move
  3. Current flows
  4. Voltage is generated

Answer.1. Pointer moves

Explanation:

In a Dynamometer type wattmeter, the current coil carries the load current and the potential coil carries current proportional to the load voltage. Due to currents in the coils, mechanical force exists between them. The result is that the movable coil moves the pointer over the scale. The pointer comes to rest at a position where deflecting torque is equal to the controlling torque.

 

4.  In D.C. circuits, power is measured using ________

  1. Ohmmeter and galvanometer
  2. Ohmmeter and voltmeter
  3. Ammeter and voltmeter
  4. Ammeter and galvanometer

Answer.3. Ammeter and voltmeter

Explanation:

  • A voltmeter is an instrument used for measuring the electrical potential difference between two points in an electric circuit.
  • An ammeter is a measuring device used to measure the electric current in a circuit.

From Ohm’s Law

R = V/I  and P = VI

So we can measure resistance and power from the voltmeter and ammeter used together. Resistance is proportional to voltage and inversely proportional to current but power is directly proportional to both voltage and current.

A dynamometer wattmeter is almost universally used for the measurement of d.c. as well as a.c. power. It works on the dynamometer principle i.e. mechanical force exists between two current-carrying conductors or coils.

 

5. When a current-carrying coil in Dynamometer type wattmeter is placed in the magnetic field?

  1. No force is exerted
  2. Voltage is produced
  3. Power is generated
  4. A force is exerted

Answer.4. A force is exerted

Explanation:

In a Dynamometer type wattmeter, the current coil carries the load current and the potential coil carries current proportional to the load voltage. Due to currents in the coils, mechanical force exists between them. As a result, a deflection torque is generated and the moving coil undergoes deflection. The result is that the movable coil moves the pointer over the scale. The pointer comes to rest at a position where deflecting torque is equal to the controlling torque.

 

6. A dynamometer type wattmeter consists of ________

  1. Only potential coil
  2. Potential and current coils
  3. Only current coil
  4. No coils

Answer.2. Potential and current coils

Explanation:

When a dynamometer instrument is used as a wattmeter, the fixed coils are connected in series with the load and carry the load current while the moving coil is connected across the load through a series multiplier R and carries a current proportional to the load voltage. The fixed coil (or coils) is called the current coil and the movable coil is known as the potential coil.

 

7. In a Dynamometer type wattmeter, the fixed coil is split into ________ Parts.

  1. 4
  2. 3
  3. 2
  4. 1

Answer.2. Potential and current coils

Explanation:

The dynamometer-type wattmeter essentially consists of two coils called fixed coil and moving coil. The fixed coil is split into two equal parts that are placed parallel to each other. The two fixed coils are air-cored to avoid hysteresis effects when used on AC. moving coil. The fixed coil is also called the current coil as it is connected in series with the load.

 

8. Controlling torque in Dynamometer type wattmeter is provided by _____

  1. Spiral Spring
  2. Hair Spring
  3. Gold Spring
  4. Control Spring

Answer.1. Spiral Spring

Explanation:

In Dynamometer type wattmeter the controlling torque is provided by a pair of spiral type hair springs fixed on the spindle. These hairs prings also provide the path for the current flow into and out of the moving coil, M.

 

9.  The controlling torque in Dynamometer type wattmeter is provided by the

  1. Eddy current Damping
  2. Air Friction Damping
  3. Fluid Friction Damping
  4. Electromagnetic Damping

Answer.2. Air Friction Damping

Explanation:

In Dynamometer type wattmeter for controlling torque the damping of the moving system is provided using an air friction damping mechanism. Here, the moving system carries a light aluminum vane that moves in a sector-shaped enclosure providing damping.

 

10. The fixed coil of dynamometer type wattmeter is made up of

  1. Thin wire
  2. Thick Wire
  3. Either Thin wire and Thick wire
  4. None of the above

Answer.2. Thick Wire

Explanation:

In Dynamometer type wattmeter the fixed coils carry the load current which may be high. So the winding wires used should be thick enough so that the coil can carry that current.

 

11. The moving coil of dynamometer type wattmeter is made up of

  1. Thin wire
  2. Thick Wire
  3. Either Thin wire and Thick wire
  4. None of the above

Answer.1. Thin wire

Explanation:

In Dynamometer type wattmeter the moving coil is connected in parallel with the load and carries the current proportional to the voltage applied across the load. It is, therefore, called a potential coil.

Generally, a high resistance is connected in series with the moving coil to limit the current through it. By limiting the current, the moving coil is made thin and light in weight which in turn increases the sensitivity of the instrument.

 

12. The fixed coil in dynamometer type wattmeter is also called as ______

  1. Pressure Coil
  2. Current Coil
  3. Power Coil
  4. Resistance Coil

Answer.2. Current Coil

Explanation:

An electrodynamometer-type wattmeter is made up of two coils, namely, a fixed coil and a moving coil. The fixed coil is split into two parts. The fixed coil is also called the current coil as it is connected in series with the load. It carries the load current.

The moving coil is connected in parallel with the load. Full voltage is applied across the moving coil and hence it is also called the pressure coil.

 

13. The moving coil in dynamometer type wattmeter is also called as ______

  1. Pressure Coil
  2. Current Coil
  3. Power Coil
  4. Resistance Coil

Answer.1. Pressure Coil

Explanation:

An electrodynamometer-type wattmeter is made up of two coils, namely, a fixed coil and a moving coil.  The moving coil is connected in parallel with the load. Full voltage is applied across the moving coil and hence it is also called the pressure coil.

 

14. A dynamometer type wattmeter has

  1. Square law scale
  2. Non-linear scale
  3. Logarithmic scale
  4. Uniform scale

Answer.4. Uniform scale

Explanation:

In dynamometer type wattmeter, the scale of the instrument is uniform because deflecting torque is proportional to the true power in both DC as well as AC and the instrument is spring controlled.

${T_d} = \frac{P}{{{R_s}}}\frac{{dM}}{{d\theta }}#

High degree of accuracy can be obtained by careful design; hence these are used for calibration purposes.

 

15. When the current is reversed in dynamometer type wattmeter then the direction of deflection torque _____

  1. Becomes Negative
  2. Becomes More Positive
  3. Remain Unchanged
  4. All of the above

Answer.3. Remain Unchanged

Explanation:

In dynamometer type wattmeter reversal of current reverses currents in both the fixed coils and the movable coil so that the direction of deflecting torque remains unchanged. Hence, such instruments can be used for the measurement of d.c. as well as a.c. power.

In the case of the AC system, the direction of flow of current is reversed in both the coils simultaneously in the negative half cycle, but the direction of deflecting torque produced in the moving system remains the same. Hence, the dynamometer-type wattmeter can be used on DC as well as on the AC supply systems.

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