Practice important
Dielectric Strength
MCQ questions and answers.
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MCQ Questions
1. What is meant by the dielectric strength of an insulating material?
A.
The maximum electric field the material can withstand without electrical breakdown
B.
The amount of heat stored by the material
C.
The resistance of the material to mechanical bending
D.
The ability of the material to conduct electric current easily
Correct Answer:
The maximum electric field the material can withstand without electrical breakdown
Explanation:
Dielectric strength is the maximum electric field an insulator can withstand before it breaks down and starts conducting significantly.
2. What is the SI unit of dielectric strength?
A.
Ohm
B.
Volt per metre
C.
Coulomb
D.
Farad
Correct Answer:
Volt per metre
Explanation:
Dielectric strength is a maximum electric field, and electric field is measured in volts per metre (V/m).
3. An insulator with a higher dielectric strength can withstand:
A.
A stronger electric field before breakdown
B.
A lower temperature only
C.
Less electric field before breakdown
D.
No electric field at all
Correct Answer:
A stronger electric field before breakdown
Explanation:
A higher dielectric strength means the insulator can tolerate a greater electric field without losing its insulating property.
4. What happens when the electric field applied to an insulator exceeds its dielectric strength?
A.
The insulator becomes a perfect vacuum
B.
Electrical breakdown occurs
C.
The electric field becomes zero automatically
D.
The material becomes colder
Correct Answer:
Electrical breakdown occurs
Explanation:
Exceeding the dielectric strength causes electrical breakdown, allowing the insulator to conduct a significant current.
5. Which material is generally used as an insulator because it has high dielectric strength?
A.
Copper
B.
Aluminium
C.
Porcelain
D.
Silver
Correct Answer:
Porcelain
Explanation:
Porcelain is an insulating material with high dielectric strength, so it can withstand strong electric fields before breakdown.
6. If the dielectric strength of an insulating material is 2 x 10^6 V/m, what does this value indicate?
A.
The material breaks down at an electric field of about 2 x 10^6 V/m
B.
The material conducts perfectly at 2 V/m
C.
The material stores 2 x 10^6 coulombs
D.
The material has a resistance of 2 x 10^6 ohms
Correct Answer:
The material breaks down at an electric field of about 2 x 10^6 V/m
Explanation:
The dielectric strength gives the approximate maximum electric field the insulator can withstand before electrical breakdown.
7. For the same applied voltage, which insulator is less likely to undergo breakdown?
A.
The one with lower dielectric strength
B.
The one with higher dielectric strength
C.
The one with zero dielectric strength
D.
The one that is already conducting
Correct Answer:
The one with higher dielectric strength
Explanation:
An insulator with higher dielectric strength can withstand a larger electric field, making breakdown less likely under the same conditions.
8. If the thickness of an insulating layer is increased while its dielectric strength remains constant, its breakdown voltage will generally:
A.
Increase
B.
Decrease to zero
C.
Remain unrelated to the thickness
D.
Become equal to its resistance
Correct Answer:
Increase
Explanation:
The breakdown voltage is approximately the product of dielectric strength and thickness, so a thicker insulating layer can withstand a higher voltage.
9. Which of the following is a common example of electrical breakdown in an insulator?
A.
A spark passing through air at a sufficiently high electric field
B.
A bulb glowing because of a battery
C.
A magnet attracting iron
D.
Water freezing in a container
Correct Answer:
A spark passing through air at a sufficiently high electric field
Explanation:
Air normally acts as an insulator, but when the electric field exceeds its dielectric strength, it breaks down and a spark can pass through it.
10. Which property is most important when selecting an insulating material for high-voltage use?
A.
High dielectric strength
B.
High electrical conductivity
C.
Very low melting point
D.
Low resistance to breakdown
Correct Answer:
High dielectric strength
Explanation:
High-voltage insulation must withstand strong electric fields without electrical breakdown, so high dielectric strength is essential.