| 1. |
In electric circuits, ‘inductance’ is the property of a circuit which:
| A. |
produces a voltage in a conductor |
| B. |
causes the circuit current to increase |
| C. |
remains at a constant value at switch on and switch off |
| D. |
prevents any opposition to voltage flow |
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| 2. |
Inductors have the effect of storing current as an electromagnetic field whenever the current increases and:
| A. |
storing voltage when the current decreases |
| B. |
giving it back when the current decreases |
| C. |
remaining constant when the current decreases |
| D. |
storing current as resistance when the current decreases |
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| 3. |
Look at the diagram: 
The following diagram shows the symbol for a:
| B. |
ferrite cored indictor |
| D. |
epoxy-resin cored inductor |
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| 4. |
An EMF can be induced in a conductor if there is a relative movement between a conductor and:
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| 5. |
Faraday’s Law of electromagnetic induction states that the value of the EMF induced in a circuit depends on the number of conductors in the circuit and the rate of change of the:
| A. |
magnetic flux linking the conductors |
| B. |
electrostatic flux linking the conductors |
| C. |
voltage linking the conductors |
| D. |
magnetic current flowing through the air-gap |
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| 6. |
The following formula can be used to determine the voltage induced in a conductor by a moving magnetic field: 
In the formula, the ø stands for the:
| A. |
change in magnetic voltage |
| B. |
magnetic flux in webers |
| C. |
time period for the magnetic change |
| D. |
number of conductors cut by the magnetic field |
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| 7. |
A coil of 400 turns is cut by a magnetic field of 0.15 Wb in 4 seconds. The voltage induced in the coil will be:
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| 8. |
The EMF generated in a conductor can be determined using the following formula: 
In the formula the θ symbol stands for the:
| A. |
flux density of the magnetic field in teslas |
| B. |
velocity of the conductor in metres per second |
| C. |
length of the conductors being cut by the magnetic field |
| D. |
angle at which the magnetic field cuts the conductors |
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| 9. |
A 15 cm conductor is rotated within a magnetic field of a constant density of 0.8 Tesla. If the velocity relative to the field is 12 m per second, then the voltage generated at a cutting angle of 45º will be:
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| 10. |
The inductive effect of Lenz’s law is such that the induced current will appear in such a direction that it:
| A. |
is always in the same direction as the change that produced it |
| B. |
opposes the change that produced it |
| C. |
acts to assist the change that produced it |
| D. |
not induce a voltage in the conductor |
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| 11. |
Magnetic inductance occurs when a magnet:
| A. |
is used as a compass to find direction |
| B. |
has been demagnetized by a physical force |
| C. |
induces a magnetic field in another material |
| D. |
loses its magnetism due to rough handling |
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| 12. |
In an electric circuit, inductance occurs when a current in one circuit causes:
| A. |
a short circuit in an another circuit |
| B. |
the resistance of the circuit to collapse |
| C. |
the supply voltage to alternate with another circuit |
| D. |
another current to be created in that same circuit |
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| 13. |
The value of inductance in an inductor is a function of the size and number of turns in the coil, the magnetic effects of the core and the:
| A. |
flux density at which it is operating |
| B. |
size of the induction coil |
| C. |
type of core that the coil is using |
| D. |
initial resistance of the conductor in the coil |
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| 14. |
Look at the following photo: 
The photo shows:
| B. |
a laminated iron-cored inductor |
| C. |
a powered ferrite cored inductor |
|
| 15. |
The henry is the inductance of a closed circuit in which an EMF of 1 volt is produced when the electric current flowing in the circuit varies uniformly at the rate of:
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| 16. |
The EMF generated in an inductor can be determined using the following formula: 
In the formula the L symbol stands for the:
| A. |
length of the coil in meters |
| B. |
length of the conductors in meters |
| C. |
amount of time since the last induction |
| D. |
inductance of the coil in Henry |
|
| 17. |
If the current through an inductor of 1.2 H is reduced uniformly from 6 A to 1 A in 0.4s, then the value of the induced EMF will be:
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| 18. |
The current in a 150 turn coil changes from 4 amps to zero amps causing a flux change of 200 mWb. The inductance of the coil is:
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| 19. |
The following formula can be used to determine the inductance of a coil from physical quantities. 
In the formula the term μo stands for the:
| A. |
zero reference magnetic flux |
| D. |
cross section area of the coil |
|
| 20. |
An air cored coil with 50 turns of wire has been wound over a length of 100 mm on a plastic pipe with an outside diameter of 25 mm. The inductance of coil will be:
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| 21. |
The term ‘self-inductance’ is used when a conductor has a voltage induced in it by:
| A. |
its own magnetic field |
| B. |
a nearby magnetic field |
| C. |
its own electromotive force |
| D. |
a nearby electromotive force |
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| 22. |
When voltage is applied, to an inductor, a magnetic field builds up and in doing so, produces a generated voltage that:
| A. |
assists the voltage producing it |
| B. |
opposes the applied voltage |
| C. |
prevents any current flow |
| D. |
acts to keep the circuit resistive |
|
| 23. |
The inclusion of an iron core within a coil:
| A. |
prevents any build up of a magnetic field when current flow |
| B. |
decreases the field strength produced for a given current flow |
| C. |
increases the field strength produced for a given current flow |
| D. |
increases the voltage flow produced for a given current flow |
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| 24. |
With an inductor, the value of any induced voltage depends on the:
| A. |
resistance of the circuit |
| B. |
frequency of the applied voltage |
| C. |
amount of time the current is steady |
| D. |
rate of change of flux linkages |
|
| 25. |
The following diagram illustrates the relative directions and values of induced voltage during ‘circuit make’ and ‘circuit break: 
The very high self-induced voltage occurring at ‘switch off’ is due to the:
| A. |
collapsing magnetic field |
| B. |
increasing supply voltage |
| C. |
current commencing to build up |
| D. |
voltage and current locking into synchronism |
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| 26. |
When opening highly inductive circuits, it is necessary to use a bypass circuit through which the high self induced voltage may be discharged. This bypass circuit is called a:
| C. |
magnetic release circuit |
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| 27. |
Any two coils sharing a part of a magnetic field will experience:
| A. |
an increase of supply voltage |
| C. |
mutual inductance to some extent |
| D. |
some change in the number of turns |
|
| 28. |
When inductors are placed in series, the total value of the inductance is determined by:
| B. |
the inverse of the sum of the inverse inductance values |
| C. |
combining the values in parallel |
| D. |
addition of the individual inductor values |
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| 29. |
The voltage across the inductor rises almost instantaneously to a maximum when switched on:
| A. |
but the current flow takes some time to reach its maximum value |
| B. |
and will then decrease to zero instantly |
| C. |
and the current flow rises at the same rate as the applied voltage |
| D. |
and reduces to zero instantly the supply is switched off |
|
| 30. |
An inductor is therefore said to have a time constant τ = tau) which is found from the formula: 
In the formula the symbol ‘L’ stands for the:
| A. |
length of the coil in meters |
| B. |
inductance of the coil in Henry |
| C. |
length of time the current flows |
| D. |
resistance of the circuit in ohms |
|
| 31. |
The following diagram shows a time constant curve applied to the rise of current in an inductive circuit: 
Three time-constants after switch on, the current will be:
| A. |
63.2% of its final value |
| B. |
86.4% of its final value |
| C. |
98.2% of its final value |
| D. |
99.3% of its final value |
|
| 32. |
A 0.75 H choke has an internal resistance of 20 Ω. The time constant of the choke is:
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| 33. |
The energy that can be stored in the electromagnetic field around an inductor can be calculated from the following formula: 
In the formula the term ‘I’ stands for:
| A. |
current flowing in the inductor |
| B. |
intensity of the magnetic field |
| C. |
interval between the time constants |
| D. |
coil inductance in henrys |
|
| 34. |
A 6 H electromagnet with an internal resistance of 40 Ω has a current flowing through it of 5A. The energy stored in its fully charged magnetic field is:
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| 35. |
Care must be taken when working with large inductors as the energy in an inductor can be discharged very fast. This will result in the:
| A. |
build up of coil turns |
| C. |
generation of a very high voltage |
| D. |
lines of magnetic force becoming stationary |
|
| 36. |
Coils often have a magnetic core, such as laminated iron or ferrite added to:
| C. |
assist in mounting the coil |
| D. |
increase the inductance |
|
| 37. |
Toroidal cores of ceramic materials are popular in many areas of electronics and electrical engineering mainly because:
| A. |
very high value inductors are available in small physical sizes |
| B. |
very low value inductors are available in large physical sizes |
| C. |
they are not suitable for both a.c and d.c. applications |
| D. |
they can be manufactured without using any windings |
|
| 38. |
Look at the following diagram: 
The diagram illustrates the principle of operation of a Kettering ignition system. The operation of this system is based on, which is based on:
| C. |
Piezo-electric principles |
|
| 39. |
If the insulation on an inductor breaks down, it can present two common problems-shorted turns and:
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| 40. |
Broken conductors can occur in inductors, usually due to:
| C. |
the current being too small |
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| 41. |
The insulation resistance of inductors with more than one coil should be tested between coils and an insulation value greater than:
| A. |
1 MΩ should be expected |
| B. |
2 MΩ should be expected |
| C. |
5 MΩ should be expected |
| D. |
10 MΩ should be expected |
|
| 42. |
The resistance of inductors can be measured to ensure that the coil has continuity. This test ensures that the:
| A. |
current will continue through to the Earthing medium |
| B. |
resistance of the coil is the correct value |
| C. |
insulation resistance of the coil is low enough |
| D. |
applied voltage will not be connected to the frame |
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| 43. |
Before putting into service, relays using induction coils, should be given an insulation resistance test, a continuity test and:
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