This Portion of Electrical andElectronic Measurements and Measuring instruments contains Magnetic Measurements MCQs (Multiple Choice Questions and Answers) / Objective Type Questions and Answers.

This Section covers below lists of topics.

1. Types of Tests
2. Ballistic Tests
3. Permeameters
4. Measurement of Leakage Factor with Flux Meter
5. Alternating Current Magnetic Testing
6. Methods of measurement of Iron Losses
7. Methods of measurement of Air Gap Flux
8. Testing of Permanent Magnets

PRACTICE IT NOW TO SHARPEN YOUR CONCEPT AND KNOWLEDGE

#### 1. Which of the following measures the magnetic flux density?

• Ballistic galvanometer
• Grassot fluxmeter
• Permeameter
• All of the above

#### 2. When a magnetic material is subjected to alternating field, loss of power occurs owing to

• hysteresis only
• eddy current only
• both hysteresis and eddy currents
• none of the above

#### 3. The area of the hysteresis loop in magnetic specimen indicates

• hysteresis and eddy current loss
• hysteresis loss
• hysteresis loss per unit volume
• hysteresis loss per unit volume per cycle of frequency

#### 4. The ratio of total flux to the useful flux in a magnetic circuit is called

• form factor
• leakage factor
• utility factor
• dispersion factor

#### 5. Maxwell’s bridge method is used to measure

• iron loss and permeability
• copper loss
• copper loss and iron loss
• none of these

#### 6. Ballistic tests are used in magnetic measurements for :

• Determination of B-H curve of the specimen only
• Determination of hysteresis loop of the specimen only
• Determination of flux density, magnetizing force and B-H curve and hysteresis loop of the specimen
• Finding out iron losses in the specimen.

#### 7. The true value of flux density in a ring specimen is ____________ Where B’ = measured value of the flux density, H = magnetizing force. As = area of cross section of specimen Ac = area of cross section of coil producing magnetizing force.

• B = B’ + µ0H(Ac/As -1)
• B = B’ - µ0H(Ac/As -1)
• B = B’ + µ0H(As/Ac -1)
• B = B’ - µ0H(As/Ac -1)

#### 8. The reason for using ring type specimens for ballistic tests is :

• They are free from end effects
• They require less labour to prepare as compared with bar type specimens
• They can be used for large quantities of materials of very small permeability
• All the above.

#### 9. Burrow’s  permeameter is preffered to other permeameters as it :

• Incorporate arrangement for uniform distribution of mmf over the entire length of the specimen
• Incorporate arrangement for elimination of leakage flux at the joints
• Is very accurate and can serve as reference standard
• All the above.

#### 10. In an Epstein square, used for finding the iron loss in a stack of laminations, the laminations are so arranged that

• Plane of each lamination is perpendicular to the plane of the square
• Plane of each lamination is parallel to the plane of square
• The plane of laminations may be either parallel or perpendicular to the plane of the square
• The plane of laminations may be at any angle to the plane of square.

#### 11. In a Lloyd Fisher square used for determination of iron loss in a specimen of iron laminations, the current coil of the wattmeter is connected in the primary winding circuit, while the pressure coil is connected in the secondary winding circuit. This is done so that :

• The I2R losses in the current coil are not included in the wattmeter reading
• The I2R losses in the pressure coil circuit are not included in the wattmeter reading
• The I2R losses both in current coil and pressure coil circuit are not included in the wattmeter reading
• The wattmeter reads only the iron losses in the specimen of laminations.

#### 12. Iron losses in a specimen of iron are determined by using co-ordinate type of potentiometer. The loss component of no load current is ready by :

• Inphase potentiometer
• Either by inphase or Quadrature potentiometer.
• None of the above.

#### 13. The iron loss when measured in the specimen of laminations at a constant maximum flux density of 1.3 Wb/m2 are : 20W at 40 Hz and 40 W a 60 Hz. What are the hysteresis and eddy current losses at 50Hz and a flux density of 1.3 Wb/m2 ?

• 10W, 20 W
• 7.38W, 212.8 W
• 8.38W, 20.8W
• 5W,25W

• H = f / vp
• H = 2πf / h
• H = fh / 4π
• H = 2πf / vp

#### 15. Permanent magnets are tested by :

• Ballistic methods
• Using an electric circuit having a mutual inductance
• Potentiometric methods
• Betteridge apparatus.

Share with :