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TUTOR WAVE
PHY 102 – CHAPTER 4
ELECTRIC FLUX, GAUSS'S LAW AND APPLICATIONS
A. IMPORTANT KEYWORDS
Electric Flux (Φ)
Electric Field Intensity (E)
Gauss's Law
Gaussian Surface
Closed Surface
Area Vector
Electric Field Lines
Permittivity of Free Space (ε₀)
Surface Charge Density (σ)
Linear Charge Density (λ)
Dielectric Constant (K)
Electric Charge
Positive Charge
Negative Charge
Electric Field
Coulomb's Law
Infinite Line Charge
Plane Sheet Charge
Charged Ring
Charged Conductor
Symmetrical Charge Distribution
Net Electric Flux
Electric Source
Electric Sink
Electric Potential
Parallel Plate Capacitor
Condenser
Field Direction
Flux Density
Electrostatics
B. IMPORTANT FORMULAS
1. Electric Flux
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Where:
Φ = Electric Flux
E = Electric Field
A = Area
θ = Angle between E and A
Unit = N·m²/C
2. Gauss's Law
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3. Charge Enclosed
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4. Infinite Line Charge
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Where:
λ = Linear Charge Density
r = Distance from line charge
5. Electric Field Due to Charged Ring
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6. Plane Sheet Charge
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7. Plane Charged Conductor
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8. Surface Charge Density
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9. Linear Charge Density
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C. 50 CBT QUESTIONS
1.
Electric flux is represented by: A. E B. Φ C. σ D. λ
Answer: B
2.
The SI unit of electric flux is: A. N·m²/C B. N/C C. J/C D. C/N
Answer: A
3.
Electric flux is a: A. Vector B. Tensor C. Scalar D. Force
Answer: C
4.
Gauss's law applies to: A. Open surfaces B. Closed surfaces C. Conductors only D. Insulators only
Answer: B
5.
The symbol ε₀ represents: A. Charge B. Area C. Permittivity of free space D. Flux
Answer: C
6.
Electric flux measures: A. Potential difference B. Number of field lines C. Resistance D. Current
Answer: B
7.
The area vector of a closed surface points: A. Inward B. Downward C. Upward D. Outward
Answer: D
8.
Flux is zero when the surface is: A. Perpendicular to E B. Parallel to E C. Circular D. Closed
Answer: B
9.
The Gaussian surface must be: A. Open B. Closed C. Flat D. Conducting
Answer: B
10.
Gauss's law relates flux to: A. Voltage B. Resistance C. Enclosed charge D. Current
Answer: C
11.
The charge enclosed by a Gaussian surface is: A. Φ/ε₀ B. Φε₀ C. EA D. qE
Answer: B
12.
A positive charge acts as: A. Sink B. Source C. Conductor D. Capacitor
Answer: B
13.
A negative charge acts as: A. Source B. Sink C. Flux D. Current
Answer: B
14.
The field lines from a positive charge: A. Enter B. Leave C. Disappear D. Rotate
Answer: B
15.
The field lines toward a negative charge: A. Leave B. Remain constant C. Enter D. Rotate
Answer: C
16.
The electric field at the centre of a charged ring is: A. Infinite B. Zero C. Maximum D. Constant
Answer: B
17.
The symbol λ denotes: A. Surface charge density B. Flux C. Linear charge density D. Potential
Answer: C
18.
The symbol σ denotes: A. Surface charge density B. Flux C. Area D. Charge
Answer: A
19.
The dielectric constant is represented by: A. E B. λ C. K D. Φ
Answer: C
20.
Electric flux is maximum when θ equals: A. 0° B. 45° C. 60° D. 90°
Answer: A
21.
cos 90° equals: A. 1 B. 0 C. 2 D. -1
Answer: B
22.
If no charge is enclosed, net flux is: A. Infinite B. One C. Zero D. Negative
Answer: C
23.
Gauss's law is a restatement of: A. Ohm's law B. Newton's law C. Coulomb's law D. Hooke's law
Answer: C
24.
The electric field of an infinite line charge varies as: A. r² B. r C. 1/r D. 1/r²
Answer: C
25.
The field between capacitor plates is: A. Zero B. Uniform C. Circular D. Infinite
Answer: B
26.
Electric field lines never: A. Cross one another B. Originate from charges C. Terminate on charges D. Show field direction
Answer: A
27.
The electric field due to a positively charged infinite plane sheet is: A. Zero B. Variable C. Circular D. Uniform
Answer: D
28.
The unit of surface charge density (σ) is: A. C/m B. C/m² C. N/C D. V/m
Answer: B
29.
The unit of linear charge density (λ) is: A. C/m² B. N/C C. C/m D. J/C
Answer: C
30.
For electric flux, θ is the angle between: A. Electric field and area vector B. Charge and area C. Field and charge D. Flux and area
Answer: A
31.
Electric flux through a surface is negative when: A. Field leaves the surface B. Field enters the surface C. Surface area is zero D. Charge is positive
Answer: B
32.
The total flux through a closed surface depends on: A. Surface shape B. Surface area C. Position of charges outside D. Net enclosed charge
Answer: D
33.
A spherical Gaussian surface is most suitable for: A. Line charge B. Plane charge C. Point charge D. Ring charge
Answer: C
34.
The electric field inside a hollow conducting shell is: A. Zero B. Infinite C. Maximum D. Variable
Answer: A
35.
Electric field lines are directed from: A. Negative to positive B. Positive to negative C. East to west D. North to south
Answer: B
36.
The SI unit of permittivity is: A. N/C B. C/m² C. V/m D. C²/(N·m²)
Answer: D
37.
For an infinite line charge, doubling the distance r causes E to: A. Double B. Remain constant C. Reduce by half D. Become zero
Answer: C
38.
The symbol Φ represents: A. Electric Flux B. Electric Field C. Potential Difference D. Charge Density
Answer: A
39.
A Gaussian surface can be: A. Open only B. Any closed surface C. Circular only D. Rectangular only
Answer: B
40.
The electric field due to an infinite plane sheet is: A. Inversely proportional to distance B. Directly proportional to distance C. Inversely proportional to square of distance D. Independent of distance
Answer: D
41.
The area vector of a surface has magnitude equal to: A. Electric field B. Flux C. Surface area D. Charge
Answer: C
42.
When θ = 0°, electric flux is: A. Maximum B. Minimum C. Zero D. Negative
Answer: A
43.
When θ = 90°, electric flux is: A. Maximum B. Zero C. Negative D. Infinite
Answer: B
44.
A charge enclosed within a Gaussian surface produces: A. No flux B. Negative flux only C. Positive flux only D. Net electric flux
Answer: D
45.
The electric field outside a positively charged conductor is: A. Toward the conductor B. Zero C. Away from the conductor D. Circular
Answer: C
46.
Gauss's law is particularly useful for calculating electric fields of: A. Symmetrical charge distributions B. Irregular charge distributions C. Random charges D. Moving charges only
Answer: A
47.
The electric field at the centre of a uniformly charged ring is: A. Infinite B. Zero C. Maximum D. Negative
Answer: B
48.
Which quantity is a scalar? A. Electric Field B. Area Vector C. Force D. Electric Flux
Answer: D
49.
Electric field intensity is measured in: A. C/m² B. J/C C. N/C D. N·m²/C
Answer: C
50.
According to Gauss's law, if enclosed charge doubles, the electric flux: A. Remains constant B. Becomes zero C. Doubles D. Halves
Answer: C
MASTER REVISION TIP
Most Important Exam Formulas
Φ = EA cosθ
∮E·dS = q/ε₀
Q = Φε₀
E = λ/(2π ε₀ r)
E = σ/(2ε₀K)
E = σ/ε₀
σ = Q/A
λ = Q/L