2026 TESU Physics 116 Final Exam New Latest
Version with All the Questions and answers
Question 1
In electrostatic equilibrium, the electric field anywhere inside a conductor must be:
A) Zero
B) Constant but non-zero
C) Equal to the surface field
D) Directed tangentially
Correct Answer: A) Zero
Rationale: Free charges inside a conductor rearrange themselves until any internal electric field
is completely cancelled. If E were not zero, charges would continue moving — contradicting the
condition of electrostatic equilibrium. This is why cavities inside conductors are natural Faraday
shields.
Question 2
The SI unit of electric potential difference is:
A) Volt (V)
B) Ampere (A)
C) Ohm (Ω)
D) Coulomb (C)
Correct Answer: A) Volt (V)
Rationale: Electric potential difference is work done per unit charge: 1 V = 1 J/C. All other
options are units of current, resistance, or charge.
Question 3
Two point charges +Q and –Q are placed 2d apart. At the exact midpoint between them, the net
electric field is:
A) Zero
B) Directed toward +Q
C) Directed toward –Q
D) Infinite
Correct Answer: A) Zero
Rationale: Both charges produce electric fields of equal magnitude at the midpoint but in
exactly opposite directions → vector sum = 0. This point lies on the perpendicular bisector of an
electric dipole.
Question 4
Gauss’s law in SI units states that the net electric flux through any closed surface equals:
A) Qₑₙcₗₒₛₑd / ε₀
B) Qₑₙcₗₒₛₑd × ε₀
C) Qₑₙcₗₒₛₑd / μ₀
D) Zero always
Correct Answer: A) Qₑₙcₗₒₛₑd / ε₀
Rationale: ∮ E · dA = Qₑₙcₗₒₛₑd / ε₀ is one of Maxwell’s four equations and the mathematical
statement of Gauss’s law.
Question 5
A parallel-plate capacitor has capacitance C. If the plate separation is doubled (area and charge
,unchanged), the new capacitance becomes:
A) C/2
B) C/4
C) 2C
D) Remains C
Correct Answer: A) C/2
Rationale: C = ε₀A/d. Doubling d halves the capacitance because electric field strength halves
for the same charge, so V doubles and C = Q/V halves.
(Continuing immediately with the same ultra-clean spacing)
Question 6
The stored energy in a charged capacitor is correctly given by all of the following EXCEPT:
A) ½ CV²
B) ½ QV
C) Q²/(2C)
D) CV
Correct Answer: D) CV
Rationale: The three equivalent correct expressions are ½ CV² = ½ QV = Q²/(2C). CV has
incorrect dimensions for energy (it would be charge × voltage²).
Question 7
The time constant τ of a series RC circuit is:
A) RC
B) R/C
C) 1/RC
D) √(RC)
Correct Answer: A) RC
Rationale: τ = RC has units of seconds and determines how fast the capacitor charges or
discharges (63% in one time constant, 99.3% in 5τ).
Question 8
When a fully charged capacitor discharges through a resistor, the current in the circuit:
A) Decays exponentially to zero
B) Decays linearly to zero
C) Remains constant
D) Increases with time
Correct Answer: A) Decays exponentially to zero
Rationale: The discharge equation is I(t) = (V₀/R) e^(–t/RC) = I₀ e^(–t/τ). The current drops to
37% of its initial value after one time constant and approaches zero exponentially.
Question 9
A straight wire carrying current I is placed perpendicular to a uniform magnetic field B. The
magnitude of the force on the wire of length L is:
A) ILB
B) ILB sinθ (θ = 90° → maximum)
C) Zero
D) μ₀I/(2πr)
Correct Answer: A) ILB
Rationale: F = I(L × B) → magnitude ILB sinθ. Since θ = 90°, sin90° = 1 → maximum force
ILB.
, Question 10
The direction of the magnetic force on a positive charge moving with velocity v in magnetic field
B is correctly given by:
A) Right-hand rule (fingers in v, curl toward B, thumb = F)
B) Left-hand rule
C) Either hand
D) There is no force
Correct Answer: A) Right-hand rule
Rationale: Standard convention for F = q(v × B). For positive charge, right-hand rule gives the
correct direction.
Question 11
The magnetic field inside a long solenoid (n turns per unit length, current I) is:
A) B = μ₀nI (uniform and parallel to axis)
B) B = μ₀I/(2πr)
C) B = 0
D) B = μ₀I only
Correct Answer: A) B = μ₀nI
Rationale: Derived using Ampère’s law on a rectangular loop; field outside is essentially zero,
inside uniform μ₀nI.
Question 12
Faraday’s law of electromagnetic induction is expressed as:
A) ε = –dΦ_B/dt
B) ε = –N dΦ_B/dt (for a coil of N turns)
C) Both are correct
D) ε = Bℓv only
Correct Answer: C) Both are correct
Rationale: Single loop: ε = –dΦ/dt. For N identical turns: ε = –N dΦ/dt.
Question 13
Lenz’s law states that the induced current flows in a direction so that its own magnetic field:
A) Opposes the change in external magnetic flux
B) Adds to the change in external flux
C) Is perpendicular to the change
D) Is zero
Correct Answer: A) Opposes the change in external magnetic flux
Rationale: Direct consequence of energy conservation. If it reinforced the change, energy would
increase indefinitely.
Question 14
In an ideal transformer, if the secondary has 5 times as many turns as the primary, the voltage is:
A) Stepped up by a factor of 5
B) Stepped down by a factor of 5
C) Unchanged
D) Stepped up by a factor of 25
Correct Answer: A) Stepped up by a factor of 5
Rationale: Vₛ/Vₚ = Nₛ/Nₚ = 5 → Vₛ = 5 Vₚ (current is stepped down by the same factor).
Question 15
The speed of all electromagnetic waves in free space is:
Version with All the Questions and answers
Question 1
In electrostatic equilibrium, the electric field anywhere inside a conductor must be:
A) Zero
B) Constant but non-zero
C) Equal to the surface field
D) Directed tangentially
Correct Answer: A) Zero
Rationale: Free charges inside a conductor rearrange themselves until any internal electric field
is completely cancelled. If E were not zero, charges would continue moving — contradicting the
condition of electrostatic equilibrium. This is why cavities inside conductors are natural Faraday
shields.
Question 2
The SI unit of electric potential difference is:
A) Volt (V)
B) Ampere (A)
C) Ohm (Ω)
D) Coulomb (C)
Correct Answer: A) Volt (V)
Rationale: Electric potential difference is work done per unit charge: 1 V = 1 J/C. All other
options are units of current, resistance, or charge.
Question 3
Two point charges +Q and –Q are placed 2d apart. At the exact midpoint between them, the net
electric field is:
A) Zero
B) Directed toward +Q
C) Directed toward –Q
D) Infinite
Correct Answer: A) Zero
Rationale: Both charges produce electric fields of equal magnitude at the midpoint but in
exactly opposite directions → vector sum = 0. This point lies on the perpendicular bisector of an
electric dipole.
Question 4
Gauss’s law in SI units states that the net electric flux through any closed surface equals:
A) Qₑₙcₗₒₛₑd / ε₀
B) Qₑₙcₗₒₛₑd × ε₀
C) Qₑₙcₗₒₛₑd / μ₀
D) Zero always
Correct Answer: A) Qₑₙcₗₒₛₑd / ε₀
Rationale: ∮ E · dA = Qₑₙcₗₒₛₑd / ε₀ is one of Maxwell’s four equations and the mathematical
statement of Gauss’s law.
Question 5
A parallel-plate capacitor has capacitance C. If the plate separation is doubled (area and charge
,unchanged), the new capacitance becomes:
A) C/2
B) C/4
C) 2C
D) Remains C
Correct Answer: A) C/2
Rationale: C = ε₀A/d. Doubling d halves the capacitance because electric field strength halves
for the same charge, so V doubles and C = Q/V halves.
(Continuing immediately with the same ultra-clean spacing)
Question 6
The stored energy in a charged capacitor is correctly given by all of the following EXCEPT:
A) ½ CV²
B) ½ QV
C) Q²/(2C)
D) CV
Correct Answer: D) CV
Rationale: The three equivalent correct expressions are ½ CV² = ½ QV = Q²/(2C). CV has
incorrect dimensions for energy (it would be charge × voltage²).
Question 7
The time constant τ of a series RC circuit is:
A) RC
B) R/C
C) 1/RC
D) √(RC)
Correct Answer: A) RC
Rationale: τ = RC has units of seconds and determines how fast the capacitor charges or
discharges (63% in one time constant, 99.3% in 5τ).
Question 8
When a fully charged capacitor discharges through a resistor, the current in the circuit:
A) Decays exponentially to zero
B) Decays linearly to zero
C) Remains constant
D) Increases with time
Correct Answer: A) Decays exponentially to zero
Rationale: The discharge equation is I(t) = (V₀/R) e^(–t/RC) = I₀ e^(–t/τ). The current drops to
37% of its initial value after one time constant and approaches zero exponentially.
Question 9
A straight wire carrying current I is placed perpendicular to a uniform magnetic field B. The
magnitude of the force on the wire of length L is:
A) ILB
B) ILB sinθ (θ = 90° → maximum)
C) Zero
D) μ₀I/(2πr)
Correct Answer: A) ILB
Rationale: F = I(L × B) → magnitude ILB sinθ. Since θ = 90°, sin90° = 1 → maximum force
ILB.
, Question 10
The direction of the magnetic force on a positive charge moving with velocity v in magnetic field
B is correctly given by:
A) Right-hand rule (fingers in v, curl toward B, thumb = F)
B) Left-hand rule
C) Either hand
D) There is no force
Correct Answer: A) Right-hand rule
Rationale: Standard convention for F = q(v × B). For positive charge, right-hand rule gives the
correct direction.
Question 11
The magnetic field inside a long solenoid (n turns per unit length, current I) is:
A) B = μ₀nI (uniform and parallel to axis)
B) B = μ₀I/(2πr)
C) B = 0
D) B = μ₀I only
Correct Answer: A) B = μ₀nI
Rationale: Derived using Ampère’s law on a rectangular loop; field outside is essentially zero,
inside uniform μ₀nI.
Question 12
Faraday’s law of electromagnetic induction is expressed as:
A) ε = –dΦ_B/dt
B) ε = –N dΦ_B/dt (for a coil of N turns)
C) Both are correct
D) ε = Bℓv only
Correct Answer: C) Both are correct
Rationale: Single loop: ε = –dΦ/dt. For N identical turns: ε = –N dΦ/dt.
Question 13
Lenz’s law states that the induced current flows in a direction so that its own magnetic field:
A) Opposes the change in external magnetic flux
B) Adds to the change in external flux
C) Is perpendicular to the change
D) Is zero
Correct Answer: A) Opposes the change in external magnetic flux
Rationale: Direct consequence of energy conservation. If it reinforced the change, energy would
increase indefinitely.
Question 14
In an ideal transformer, if the secondary has 5 times as many turns as the primary, the voltage is:
A) Stepped up by a factor of 5
B) Stepped down by a factor of 5
C) Unchanged
D) Stepped up by a factor of 25
Correct Answer: A) Stepped up by a factor of 5
Rationale: Vₛ/Vₚ = Nₛ/Nₚ = 5 → Vₛ = 5 Vₚ (current is stepped down by the same factor).
Question 15
The speed of all electromagnetic waves in free space is:
