A. Point charge
B. Sheet charge
C. Line charge
D. Point, sheet, and line charge
Answer: D
Gauss law states that the total electric flux through any closed surface is equal to the charge enclosed by that surface. Hence it applies to all points, surfaces, and volumes.
82. “Total electric flux through any closed surface is equal to the charge enclosed by that surface divided by permittivity”. This is the statement for?
A. Gauss law
B. Lenz law
C. Columb’s law
D. Faraday’s law
Answer: A
The total electric flux through any closed surface is equal to the charge enclosed by that surface divided by permittivity is the statement for Gauss law because, among the four laws, Gauss law deals with electric flux.
83. Electric flux density is a function of _______
A. Volume
B. Charge
C. Current
D. Voltage
Answer: B
Electric flux density is the charge per unit area. Hence it is a function of charge and not any of the other values.
84. As charge increases, what happens to flux density?
A. Increases
B. Decreases
C. Remains constant
D. Becomes zero
Answer: A
Electric flux density is the charge per unit area.
The expression for flux density is:
D = Q/A.
Electric flux is directly proportional to charge, hence as charge increases, electric flux also increases.
85. As the area increases, what happens to electric flux density?
A. Increases
B. Decreases
C. Remains constant
D. Becomes zero
Answer: B
Electric flux density is the charge per unit area.
The expression for flux density is:
D = Q/A.
Electric flux is inversely proportional to area, hence an area increases, electric flux decreases.
86. Which among the following is the correct expression for electric flux density?
A. D = ε × E
B. D = ε/E
C. D2 = ε × E
D. D = ε × E2
Answer: A
Electric flux density is directly proportional to the electric field, ε(permittivity of free space) being the constant of proportionality.
Hence D = ε × E.
87. Strength of the electric field is ___________
A. Directly proportional to the force applied
B. Inversely proportional to the force applied
C. Directly proportional to the square of the force applied
D. Inversely proportional to the square of the force applied
Answer: A
The strength of the electric field is directly proportional to the force applied.
Electric field intensity is the force per unit charge, hence it is directly proportional to the force applied.
88. The force applied to a conductor is 10N if the charge in the conductor is 5C, what is the electric field intensity?
A. 10V/m
B. 2V/m
C. 3V/m
D. 15V/m
Answer: B
Electric field intensity is the force per unit charge. The formula is:
E = F/Q = 10/5 = 2V/m.
89. What is the electric flux density in free space if the electric field intensity is 1V/m?
A. 7.76 × 10-12C/m2
B. 8.85 × 10-12C /m2
C. 1.23 × 10-12C /m2
D. 3.43 × 10-12C /m2
Answer: B
The formula for electric filed density is:
D = ε × E = 1 × 8.85 × 10-12
= 8.85 × 10-12C /m2.
90. If the charge in a conductor is 16C and the area of the cross-section is 4m2. Calculate the electric flux density.
A. 64C/m2
B. 16C/m2
C. 4C/m2
D. 2C/m2
Answer: C
Electric Flux density is the charge per unit area. The formula is:
D = Q/A
= 16/4 = 4C/m2.
91. In order to obtain a high value for capacitance, the permittivity of the dielectric medium should be?
A. Low
B. High
C. Zero
D. Unity
Answer: B
Form the expression of the capacitance of a parallel plate capacitor
C = ε × A/d.
From this expression, it is seen that capacitance is directly proportional to the permittivity, hence for the capacitance value to be high, the permittivity value should be high.
92. Find the capacitance of a capacitor whose area of a cross-section of the plates is 4m2 and the distance of separation between the plates is 2m. The capacitor is placed in a vacuum.
A. 1.77 × 10-11F
B. 1.34 × 10-11F
C. 2.33 × 10-11F
D. 5.65 × 10-11F
Answer: A
The expression for the capacitance of a parallel plate capacitor is
C = ε × A/d.
The medium is free space hence,
ε = 8.85 × 10-12.
∴ C = 8.85 × 10-12 × 4/2 = 1.77 × 10-12F
= 1.77 × 10-11F.
93. What is relative permittivity?
A. Equal to the absolute permittivity
B. Ratio of actual permittivity to absolute permittivity
C. Ratio of absolute permittivity to actual permittivity
D. Equal to the actual permittivity
Answer: B
Relative permittivity is the ratio of actual permittivity to absolute permittivity. As the actual permittivity increases, the relative permittivity also increases.
94. What happens to relative permittivity when actual permittivity decreases?
A. Increases
B. Decreases
C. Remains the same
D. Becomes zero
Answer: B
Relative permittivity is the ratio of actual permittivity to absolute permittivity. Relative permittivity is directly proportional to actual permittivity. Hence, as actual permittivity decreases, relative permittivity also decreases.
95. What is the relative permittivity when the actual permittivity is 4F/m?
A. 4.57 × 10-11
B. 4.57 × 1012
C. 4.57 × 1011
D. 4.57 × 10-12
Answer: C
Relative permittivity = Actual permittivity/ Absolute permittivity.
96. What happens to absolute permittivity when relative permittivity increases?
A. Increases
B. Decreases
C. Remains the same
D. Becomes zero
Answer: C
Absolute permittivity does not depend on the value of relative permittivity. Absolute permittivity is the permittivity of free space and it is a constant value = 8.85 × 10-12F/m.
97. Calculate the actual permittivity of a medium whose relative permittivity is 5.
A. 4.43 × 10-11F/m
B. 4.43 × 10-12F/m
C. 4.43 × 1011F/m
D. 4.43 × 1012F/m
Answer: A
Actual permittivity = Relative permittivity × absolute permittivity.
Relative permittivity is the ratio of actual permittivity to the relative permittivity of the medium. Since it is a ratio, and we know that a ratio does not have any unit, relative permittivity does not have any unit.
99. Which among the following will be unity in free space?
A. Absolute permittivity
B. Relative permittivity
C. Actual permittivity
D. Both absolute and relative permittivity
Answer: B
Relative permittivity is constant for a particular medium. For air or free space, it is unity. Absolute permittivity does not depend on the medium, its value is always constant = 8.85 × 10-12F/m.
Actual permittivity is the product of relative permittivity and absolute permittivity.
100. Which among the following do not have any unit?
A. Absolute permittivity
B. Relative permittivity
C. Actual permittivity
D. Both absolute and relative permittivity
Answer: B
Relative permittivity is the ratio of actual permittivity to the relative permittivity of the medium.
Since it is a ratio, and we know that a ratio does not have any unit, relative permittivity does not have any unit.
