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# Multiple choice question for engineering

## Set 1

1. What is a permeable substance?
a) Any good conductor
c) Any strong magnet
d) Any substance through which the magnetic lines of force can pass easily

Answer: d [Reason:] A permeable substance is one through which the magnetic lines of force can pass through easily.

2. Materials having good retentivity are?
a) Strong magnets
b) Weak magnets
c) Temporary magnets
d) Permanent magnets

Answer: c [Reason:] Materials having low retentivity are temporary magnets because they can retain the magnetic strength for only some time.

3. Magnetic field exists along which of the following?
a) Moving charges
b) Stationary charges
c) Copper
d) Iron

Answer: a [Reason:] Moving charges have a magnetic field associated with them because they have magnetic flux lines associated with it.

4. The direction of magnetic lines of force are?
a) From north pole to south pole
b) From south pole to north pole
c) No specific direction
d) From one end of the magnet to the other

Answer: a [Reason:] Magnetic lines of force originate at the north pole and terminate at the south pole hence they are from the north pole to the south pole.

5. Magnetic force lines ___________ at the north pole.
a) Emerge
b) Converge
c) Neither emerge nor converge
d) Either emerge or converge

Answer: a [Reason:] Magnetic force lines emerge at the north pole. Force lines seem to emerge at the north pole because they originate at the north pole.

6. When a bar magnet is broken into two pieces, which of the following are true?
a) The magnet loses its magnetism
b) The magnet has only north pole left
c) The magnet has only south pole left
d) The magnet turns into two new bar magnets

Answer: d [Reason:] When a bar magnet is broken into two pieces, it forms two differ bar magnets. This happens because the broken pieces of the magnet forms a separate north and south pole for itself as monopoles do not exist.

7. When an electric current flows into the page, what is the direction of the magnetic field?
a) Clockwise
b) Anti-clockwise
c) Cannot be determined
d) Parallel to the current

Answer: a [Reason:] when the current flows into the page, the magnetic field is clockwise because of the right hand thumb rule, we orient our thumb into the page and our fingers curl in the clockwise direction.

8. When an electric current flows out of the page, what is the direction of the magnetic field?
a) Clockwise
b) Anti-clockwise
c) Cannot be determined
d) Parallel to the current

Answer: b [Reason:] when the current flows out of the page, the magnetic field is anti-clockwise because of the right hand thumb rule, we orient our thumb out of the page and our fingers curl in the anti-clockwise direction.

9. Which of the following is used to determine the direction of magnetic field in a current carrying conductor?
a) Left hand thumb rule
b) Right hand thumb rule
c) Right hand palm rule
d) Left hand palm rule

Answer: b [Reason:] The right hand thumb rule determines the direction of magnetic field in a current carrying conductor. The rule states that when we align our right thumb in the direction of the current and curl our fingers around it, the direction of our fingers is the direction of the magnetic field.

10. The relation between the direction of current and the direction of magnetic field is?
a) Same direction
b) Opposite direction
c) Perpendicular
d) Unrelated

Answer: c [Reason:] When a conductor carries a certain value of current, the force developed in the conductor, the current in the conductor and the magnetic field in the conductor are mutually perpendicular to each other.

## Set 2

1. The formula for induced emf is ______
a) emf=B2l
b) emf=Bil
c) emf=Blv
d) emf=B2v

Answer: c [Reason:] The formula for induced emf is: emf=Blv, where B is the magnetic field, l is the length of the conductor and v is the velocity with which it is moving in the magnetic field.

2. Which, among the following, is the formula for induced emf?
a) e=d(phi)/dt
b) e=dt/d(phi)
c) e=t*phi
d) e=t2phi

Answer: a [Reason:] The formula foe induced emf is e=d(phi)/dt because the induced emf is the flux linkage per unit time.

3. Find the length of a conductor which is moving with a velocity 0.4m/s in a magnetic field of 8T, inducing an emf of 20V.
a) 50m
b) 5m
c) 6.25m
d) 0.5m

Answer: c [Reason:] The formula for induced emf is: emf=Blv. Substituting the values of B, emf and v from the question, we get l=6.25m.

4. If a conductor 0.2m long moves with a velocity of 0.3m/s in a magnetic field of 5T, calculate the emf induced.
a) 0.3V
b) 0.03V
c) 30V
d) 3V

Answer: a [Reason:] The formula for induced emf is: emf=Blv. Substituting the values of B, l and v from the question, we get emf=0.3V.

5. What is emf?
a) Force
b) Voltage
c) Current
d) Flux

Answer: b [Reason:] Electromotive force is not actually a force. It is basically a voltage. It is the voltage developed by any source of electrical energy.

6. Find the strength of magnetic field in a conductor 0.5m long moving with a velocity of 10m/s, inducing an emf of 20V.
a) 1T
b) 2T
c) 3T
d) 4T

Answer: d [Reason:] The formula for induced emf is: emf=Blv. Substituting the values of l, emf and v from the question, we get B=4T.

7. The emf induced in a coil having N turns is?
a) e=phi/t
b) e=N*phi/t
c) e=N*phi*t
d) e=N2*phi*t

Answer: b [Reason:] The emf induced in a coil having N turns is, e=N*phi/t. This is because, the emf in a single coil is the flux linkage per unit time, that is, phi/t. Hence the flux induced in N turns is N*phi/t.

8. An E.M.F. can be induced by _______
a) Change in magnetic field
b) Change in the area of cross section
c) Change in angle between magnetic field and area
d) Change in magnetic field, area and angle

Answer: d [Reason:] The dot product of magnetic field vector and area vector. emf=BAcos(theta), hence if either of the three, that is, magnetic field, area or angle changes, thee emf will change.

9. What is the consequence of motor effect?
a) Current
b) Voltage
c) Electromagnetic induction
d) EMF

Answer: c [Reason:] Motor effect is when a current carrying conductor in a magnetic field experiences a force, hence its consequence is electromagnetic induction.

10. The total number of magnetic field lines passing through an area is termed as _______
a) Voltage
b) EMF
c) Magnetic flux
d) Magnetic flux density

Answer: b [Reason:] The number of magnetic flux lines per unit area is the magnetic flux, because flux is the number of field lines per unit area.

## Set 3

1. The maximum power drawn from source depends on__________
a) Value of source resistance
c) Both source and load resistance
d) Neither source or load resistance

Answer: b [Reason:] The maximum power transferred is equal to: I2RL, when load resistance is variable. Es2/4RL, when load impedance is variable. In both the cases, the maximum power depends on the load resistance.

2. The maximum power is delivered to a circuit when source resistance is __________ load resistance.
a) Greater than
b) Equal to
c) Less than
d) Greater than or equal to

Answer: b [Reason:] The circuit can draw maximum power only when source resistance is equal to the load resistance.

3. If source impedance is a complex number Z, then load impedance is equal to _________
a) Z’
b) -Z
c) -Z’
d) Z

Answer: a [Reason:] When Source impedance is equal to Z, its load impedance is the complex conjugate of Z which is Z’. Only under this condition maximum power can be drawn from the circuit.

4. If ZL=Zs’, then RL=?
a) -RL
b) Rs
c) -Rs
d) 0

Answer: b [Reason:] Rs is the real part of the complex number ZL. Hence when we find the complex conjugate the real part remains the same whereas the complex part acquires a negative sign.

5. Calculate the value of RL across A and B.

a) 3.45ohm
b) 2.91ohm
c) 6.34ohm
d) 1.54ohm

Answer: b [Reason:] On shorting the voltage sources: RL=3||2+4||5.

6. Calculate Eth.

a) 3.43V
b) 4.57V
c) 3.23V
d) 5.34V

Answer: b [Reason:] The two nodal equations are: (VA-10)/3+VA/2=0 (VB-20)/4+VB/3=0 On solving the two equations, we get VA=4V, VB=8.571V. VAB=VA-VB= 4.57V.

7. Calculate the maximum power transferred.

a) 1.79W
b) 4.55W
c) 5.67W
d) 3.78W

Answer: a [Reason:] The maximum power transferred= Eth2/4RL. From the previous solutions, we have Eth=4.57V and RL=2.91ohm. Substituting the given values in the formula, we get Pmax= 1.79W.

8. Does maximum power transfer imply maximum efficiency?
a) Yes
b) No
c) Sometimes
d) Cannot be determined

Answer: b [Reason:] Maximum power transfer does not imply maximum efficiency. If the load resistance is smaller than source resistance, power dissipated at the load is reduced while most of the power is dissipated at the source then the efficiency becomes lower.

9. Under the condition of maximum power efficiency is?
a) 100%
b) 0%
c) 30%
d) 50%

Answer: d [Reason:] Efficiency=output/input*100. Under maximum power conditions: Output=I2RL; Input=2*I2RL. Thus efficiency=50%.

10. Name some devices where maximum power has to be transferred to the load rather than maximum efficiency.
a) Amplifiers
b) Communication circuits
c) Both amplifiers and communication circuits
d) Neither amplifiers nor communication circuits

Answer: c [Reason:] Maximum power transfer to the load is preferred over maximum efficiency in both amplifiers and communication circuits since in both these cases the output voltage is more than the input.

## Set 4

1. The B/H characteristics can be determined using _______
a) Ammeter
b) Fluxmeter
c) Voltmeter
d) Multimeter

Answer: b [Reason:] The fluxmetter is an electronic display instrument used to measure magnetic flux of permanent magnets hence it can be used to determine B/H characteristics.

2. The B/H curve can be used to determine?
a) Iron loss
b) Hysteresis loss
c) Voltage loss
d) Eddy current loss

Answer: b [Reason:] Hysteresis loss is basically a heat loss due to the reversal of magnetisation of the transformer core whenever it is subjected to a changing magnetic field. It can be determined using the B/H curve.

3. The B/H ratio is not constant for ________
a) Diamagnetic materials
b) Ferromagnetic materials
c) Paramagnetic materials
d) Non-magnetic materials

Answer: b [Reason:] The ferromagnetic material is magnetised with varied polarity as the magnetic field is a varying one.

4. When using a fluxmeter, if the flux changes from Φ to -Φ, what happens to the current?
a) Becomes zero
b) Becomes infinity
c) Remains the same
d) Reverses

Answer: d [Reason:] When the flux changes from Φ to -Φ, the current direction will change as the direction of flux is changing.

5. Why is the coil of a ballistic galvanometer wound on a non- metallic former?
a) To minimise damping when high resistance is connected in series
b) To maximise damping when high resistance is connected in series
c) To minimise damping when high resistance is connected in parallel
d) To maximise damping when high resistance is connected in parallel

Answer: a [Reason:] The coil of ma ballistic galvanometer is wound on a nonmagnetic former in order to minimise damping when high resistance is connected in series.

6. The ballistic galvanometer is usually lightly damped so that ________
a) It can oscillate
b) It will remain stable
c) Amplitude of the first swing is very large
d) Amplitude of the first swing is very small

Answer: c [Reason:] The ballistic galvanometer is usually lightly damped so that the amplitude of its first swing is very large.

7. PMMC instruments can be used as a fluxmeters by _______
a) Using a low resistance shunt
b) Removing the control spring
c) Making the control springs having large moment of inertia
d) Using a high resistance in series

Answer: b [Reason:] A PMMC or a permanent moving magnet coil instrument can be used as a fluxmeter by removing the control spring.

8. Hysteresis loss is determined from _______
a) B/H curve
b) H/B curve
c) BH curve
d) B2H curve

Answer: c [Reason:] Hysteresis loss is basically a heat loss due to the reversal of magnetisation of the transformer core whenever it is subjected to a changing magnetic field. It can be determined using the B/H curve.

9. What is a PMMC instrument?
a) Permanent moving magnet coil instrument
b) Permanent machine magnet coil instrument
c) Permanent moving machine coil instrument
d) Premature moving magnet coil instrument

Answer: a [Reason:] A PMMC instrument is a permanent moving magnet coil instrument. It uses two magnets to create a stationary magnetic field.

10. B/H curve shows the relationship between?
a) Magnetic field strength and magnetic flux
b) Magnetic field strength and magnetic flux density
c) Current and magnetic flux density
d) Voltage and magnetic flux density

Answer: b [Reason:] The B/H curve shows the reaction between magnetic field strength and magnetic flux density.

## Set 5

1. What is the value of current in an inductive circuit when there is no applied voltage?
a) Minimum
c) Maximum
c) Zero
d) Cannot be determined

Answer: b [Reason:] The current in an inductive circuit is maximum when there is no voltage applied because the coils of the inductor store electric flux.

2. What is the current in an inductive circuit when the applied voltage is maximum?
a) Infinity
c) Maximum
c) Zero
d) Cannot be determined

Answer: c [Reason:] The current in an inductive circuit is zero or minimum when the value of the applied voltage is maximum.

3. In an inductive circuit, the voltage_______ the current?
b) Lags
c) Is greater than
d) Is less then

Answer: a [Reason:] In a pure inductive circuit the voltage leads the current and the current lags the voltage by a phase difference of 90 degrees.

4. In an inductive circuit, the current________ the voltage?
b) Lags
c) Is greater than
d) Is less then

Answer: b [Reason:] In a pure inductive circuit the voltage leads the current and the current lags the voltage by a phase difference of 90 degrees.

5. Inductor does not allow sudden changes in?
a) Voltage
b) Current
c) Resistance
d) Inductance

Answer: b [Reason:] The inductor does not allow sudden changes in current because if current changes in the inductor occurs in zero time, the voltage becomes zero which is not possible.

6. In case of Inductive circuit, Frequency is ______________ to the current.
a) Directly proportional
b) Inversely proportional
c) Unrelated
d) Much greater than

Answer: b [Reason:] Inductance is inversely proportional to current since, as the inductance increases, current decreases.

7. In a pure inductive circuit, the power factor is?
a) Maximum
b) Minimum
c) 0
d) Infinity

Answer: c [Reason:] In a pure inductive circuit, current is lagging by 90 degrees from the voltage. The power factor is the cosine of the angle in between the voltage and the current. If the angle between the voltage and current is 90, then cos90=0. Hence, the power factor is zero.

8. What is the power in a pure inductive circuit?
a) Maximum
b) Minimum
c) 0
d) Infinity

Answer: c [Reason:] The power in a pure inductive circuit is zero because the phase angle is zero, due to which the power factor is zero and hence the power is zero.

9. What is the unit for inductive reactance?
a) Henry
b) Ohm
d) Volts