31. The fixed coil of dynamometer type wattmeter is made up of
Thin wire
Thick Wire
Either Thin wire and Thick wire
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.
32. The moving coil of dynamometer type wattmeter is made up of
Thin wire
Thick Wire
Either Thin wire and Thick wire
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.
33. The fixed coil in dynamometer type wattmeter is also called as ______
Pressure Coil
Current Coil
Power Coil
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.
34. The moving coil in dynamometer type wattmeter is also called as ______
Pressure Coil
Current Coil
Power Coil
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.
35. A dynamometer type wattmeter has
Square law scale
Non-linear scale
Logarithmic scale
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.
High degree of accuracy can be obtained by careful design; hence these are used for calibration purposes.
36. When the current is reversed in dynamometer type wattmeter then the direction of deflection torque _____
Becomes Negative
Becomes More Positive
Remain Unchanged
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.
37. Induction-type wattmeter instruments are used for _______
AC Measurement
DC Measurement
AC and DC Measurement
None of the above
Answer.1. AC Measurement
Explanation:
The induction type wattmeter can be used to measure AC power only. The working of induction type wattmeter is based on the principle of electromagnetic induction. The induction wattmeter consists of two laminated electromagnets viz. Shunt Magnet and Series Magnet.
38. The two laminated iron-core electromagnets are _____
Shunt Magnets
Series Magnets
Shunt and Series Magnets
Bar Magnets
Answer.3. Shunt and Series Magnets
Explanation:
The induction type wattmeter can be used to measure AC power only. The working of induction type wattmeter is based on the principle of electromagnetic induction. The induction wattmeter consists of two laminated electromagnets viz. Shunt Magnet and Series Magnet.
The shunt magnet is excited by the current, proportional to the voltage across the load. flowing through the pressure coil and the series magnet is excited by the load current or a definite fraction of it flowing through the current coil.
39. The disc of Induction type wattmeter is made up of _____
Copper
Aluminum
Either copper and Aluminium
Steel
Answer.3. Either copper and Aluminium
Explanation:
A thin disc made of copper or aluminum pivoted at the center is placed between the shunt and series magnets so that it cuts the flux from both of the magnets. The deflecting torque is produced by the interaction of eddy currents induced in the discs and the flux inducing it.
In order to cause the resultant flux in the shunt magnet to lag in phase by exactly 90° behind the applied voltage. one or more copper rings, known as copper-shading bands are provided on one limb of the shunt magnet.
40. The deflecting torque in shunt and series magnets is produced due to _____
Hysteresis Current
Eddy Current
Electromagnetic Current
Both Eddy and Hysteresis current
Answer.2. Eddy Current
Explanation:
A thin disc made of copper or aluminum pivoted at the center is placed between the shunt and series magnets so that it cuts the flux from both of the magnets. The deflecting torque is produced by the interaction of eddy currents induced in the discs and the flux inducing it.
In order to cause the resultant flux in the shunt magnet to lag in phase by exactly 90° behind the applied voltage. one or more copper rings, known as copper-shading bands are provided on one limb of the shunt magnet.
