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 breakdown
B.
The ability of the material to conduct electric current easily
C.
The amount of charge stored by the material
D.
The resistance of the material to mechanical stretching
Correct Answer:
The maximum electric field the material can withstand without breakdown
Explanation:
Dielectric strength is the maximum electric field that an insulator can withstand before it undergoes electrical breakdown.
2. What happens when the electric field in an insulator exceeds its dielectric strength?
A.
The insulator becomes perfectly non-polar
B.
Electrical breakdown occurs
C.
The electric field becomes zero immediately
D.
The insulator gains infinite resistance
Correct Answer:
Electrical breakdown occurs
Explanation:
If the applied electric field exceeds the dielectric strength, the insulating material breaks down and may begin to conduct electricity.
3. Which of the following is a common unit of dielectric strength?
A.
Volt per metre
B.
Coulomb
C.
Ohm
D.
Farad
Correct Answer:
Volt per metre
Explanation:
Dielectric strength is an electric field, so it is commonly measured in volts per metre, although volts per millimetre is also used.
4. An insulator has a dielectric strength of 3 × 10^6 V/m. What is the maximum electric field it can withstand without breakdown?
A.
1 × 10^6 V/m
B.
2 × 10^6 V/m
C.
3 × 10^6 V/m
D.
6 × 10^6 V/m
Correct Answer:
3 × 10^6 V/m
Explanation:
The dielectric strength directly gives the maximum electric field that the insulator can withstand without electrical breakdown.
5. Which material is generally suitable for use as an insulator because it has high dielectric strength?
A.
Copper
B.
Aluminium
C.
Mica
D.
Iron
Correct Answer:
Mica
Explanation:
Mica is an insulating material with high dielectric strength, so it can withstand strong electric fields without breakdown.
6. A material with a higher dielectric strength can withstand:
A.
A stronger electric field before breakdown
B.
A weaker electric field before breakdown
C.
No electric field at all
D.
Only mechanical pressure
Correct Answer:
A stronger electric field before breakdown
Explanation:
A higher dielectric strength means that the material can tolerate a greater electric field without losing its insulating property.
7. The dielectric strength of an insulator is mainly related to its ability to resist:
A.
Electrical breakdown
B.
Magnetic attraction
C.
Gravitational force
D.
Thermal expansion only
Correct Answer:
Electrical breakdown
Explanation:
Dielectric strength measures how effectively an insulating material resists electrical breakdown under a strong electric field.
8. If the dielectric strength of an insulating sheet is 2 × 10^6 V/m and its thickness is 0.01 m, what maximum potential difference can it withstand approximately?
A.
2 × 10^4 V
B.
2 × 10^6 V
C.
2 × 10^8 V
D.
2 × 10^2 V
Correct Answer:
2 × 10^4 V
Explanation:
The maximum potential difference is given by V = E d. Thus, V = (2 × 10^6)(0.01) = 2 × 10^4 V.
9. Electrical breakdown of an insulator means that the material:
A.
Starts conducting significantly under a strong electric field
B.
Becomes completely transparent
C.
Loses all of its mass
D.
Stops responding to an electric field permanently in every case
Correct Answer:
Starts conducting significantly under a strong electric field
Explanation:
During electrical breakdown, a strong electric field causes the insulator to conduct a substantial current.
10. For safe insulation, the applied electric field should be:
A.
Greater than the dielectric strength
B.
Equal to or greater than the dielectric strength
C.
Less than the dielectric strength
D.
Unrelated to the dielectric strength
Correct Answer:
Less than the dielectric strength
Explanation:
To prevent electrical breakdown, the applied electric field must remain below the dielectric strength of the insulating material.