CUET UG Physics Booster Test 3-Faraday’s Laws and Lenz’s Law -

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CUET UG Physics Booster Test 3-Faraday’s Laws and Lenz’s Law

⏱️ 30 Minutes

❓ 20 Questions

📌 Answers are locked once submitted — results and explanations appear at the end.

CUET UG Physics Booster Test 3-Faraday’s Laws and Lenz’s Law

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QUESTION 1 OF 20

In Faraday's experiments, under which of the following conditions is an induced current observed in a coil?
1.A magnet is moved towards a stationary coil.
2.A magnet is held stationary inside the coil.
3.A current-carrying coil is moved towards another coil.
4.A steady current flow continuously in a nearby stationary coil.

Answer Review

1 In Faraday's experiments, under which of the following conditions is an induced current observed in a coil?
1.A magnet is moved towards a stationary coil.
2.A magnet is held stationary inside the coil.
3.A current-carrying coil is moved towards another coil.
4.A steady current flow continuously in a nearby stationary coil.

A 1 and 3 only

B 1 and 2 only

C 2 and 4 only

D 1, 3 and 4 only

💡 Short Explanation

1. Short Explanation

Induced current is produced only when magnetic flux changes.

Relative motion between a magnet and coil changes flux.

Relative motion between two coils changes flux.

Stationary situations with constant flux do not induce current.

✅ Correct Answer Explanation

Statement 1 is correct.

Moving a magnet towards a coil changes the magnetic flux linked with the coil, inducing current.

Statement 2 is incorrect.

A stationary magnet inside the coil produces constant flux, so no induced current is observed.

Statement 3 is correct.

Moving a current-carrying coil towards another coil changes the magnetic flux through the second coil, inducing current.

Statement 4 is incorrect.

A steady current in a stationary coil produces a constant magnetic field and hence no change in flux.

Therefore, induced current is observed only in statements 1 and 3.

Correct Answer: A. 1 and 3 only

❓ Why Other Options Are Incorrect

Option B: Includes statement 2, where flux remains constant.

Option C: Both statements involve constant flux conditions.

Option D:

🎯 Strategy

Flux-Change Analysis

Application:

Check whether magnetic flux linked with the coil changes.

Final Logic:

Changing flux → Induced current.

Constant flux → No induced current.

🧠 Memory Trick

"Change Flux → Get Current" "No Flux Change → No Induction"

📚 Class XII Physics – Part I Chapter: Electromagnetic Induction

2 Question: Match List I with List II for Faraday's Experiments

List I	List II
(1) Magnet held stationary inside coil	(a) Deflection in opposite direction compared to North pole
(2) Magnet pulled away from coil	(b) Deflection direction reverses compared to pushing
(3) Magnet pushed faster towards coil	(c) Larger deflection in galvanometer
(4) South pole pushed towards coil	(d) Zero deflection in galvanometer

A 1-d, 2-b, 3-c, 4-a

B 1-d, 2-a, 3-b, 4-c

C 1-c, 2-d, 3-a, 4-b

D 1-a, 2-b, 3-c, 4-d

💡 Short Explanation

A stationary magnet produces no change in magnetic flux. Pulling the magnet away reverses the direction of induced current. Faster motion increases the rate of flux change and induced emf. Reversing the pole reverses the direction of galvanometer deflection.

✅ Correct Answer Explanation

(1) Magnet held stationary inside coil No change in magnetic flux occurs through the coil. Hence, no induced emf is produced and the galvanometer shows zero deflection. → 1 → d → (2) Magnet pulled away from coil The change in magnetic flux is opposite to that produced when the magnet is pushed towards the coil. Therefore, the induced current and galvanometer deflection reverse direction. → 2 → b → (3) Magnet pushed faster towards coil A faster-moving magnet causes a greater rate of change of magnetic flux. Hence, a larger induced emf and larger galvanometer deflection are produced. → 3 → c → (4) South pole pushed towards coil The direction of flux change is opposite to that produced by a North pole approaching the coil. Therefore, the galvanometer deflects in the opposite direction. → 4 → a Therefore: 1 → d 2 → b 3 → c 4 → a Hence, Option A is correct.

❓ Why Other Options Are Incorrect

Option B: Incorrectly matches the effects of pulling the magnet and faster motion.
Option C: Incorrectly assigns zero deflection and opposite-direction deflection.
Option D: Incorrectly matches the stationary magnet case.

🎯 Strategy

Used

Option Grouping

Application:

Analyze how each action affects the magnetic flux through the coil.

Final Logic:

No flux change → No deflection.
Reverse motion → Reverse deflection.
Faster motion → Greater deflection.
Opposite pole → Opposite deflection.

🧠 Memory Trick

"Stationary → Zero, Faster → Bigger, South → Opposite"

📚 Topic: Experimental Observations of Induced Current in Faraday's Experiments.

3 Choose the correct EMF Magnitude Equation statements.
1. The emf is independent of the resistance of the circuit.
2. The induced current depends on the resistance of the circuit.
3. The emf depends on the total change in flux, not the rate of change.
4. Emf can be induced even in an open circuit.

A (1), (2), (4)

B (1), (2), (3)

C (2), (3), (4)

D (1), (3), (4)

💡 Short Explanation

�� EMF depends on flux change rate. �� Current depends on resistance. �� EMF exists even in open circuits.

✅ Correct Answer Explanation

Statement 1 is correct because emf depends on dΦ/dt, not resistance. → Statement 2 is correct because I = ε/R. → Statement 3 is incorrect because emf depends on the rate of change of flux. → Statement 4 is correct because emf can exist without current in an open circuit.

❓ Why Other Options Are Incorrect

�� Option B → Includes incorrect Statement 3.
�� Option C → Includes incorrect Statement 3.
�� Option D → Includes incorrect Statement 3.

🎯 Strategy

Used

�� Elimination

Application:

�� Identify the statement contradicting Faraday's law.

Final Logic:

�� EMF depends on rate of flux change.

🧠 Memory Trick

EMF Needs Flux Rate

📚 Class XII – Physics Part I – Chapter: Electromagnetic Induction – Topic: Faraday's Law

4 Identify the incorrect statement about the time derivative of flux:

A ε = -dΦB/dt signifies the time rate of change.

B A steady magnetic flux results in a zero time derivative and zero emf.

C The time derivative can be non-zero even if the magnetic field magnitude is strictly constant.

D The time derivative is maximized when a coil is held stationary in a constant magnetic field.

💡 Short Explanation

�� Stationary coil means constant flux. �� Constant flux gives zero derivative. �� No induced emf is produced.

✅ Correct Answer Explanation

When a coil is stationary in a constant magnetic field, magnetic flux remains constant. → Therefore: dΦ/dt = 0 → Hence induced emf is zero. → Option D is incorrect and is the correct answer.

❓ Why Other Options Are Incorrect

�� Option A → Correct statement of Faraday's law.
�� Option B → Correct consequence of constant flux.
�� Option C → Angle or area may change while B remains constant.

🎯 Strategy

Used

�� Elimination

Application:

�� Check which statement contradicts Faraday's law.

Final Logic:

�� Constant flux cannot produce maximum emf.

🧠 Memory Trick

Constant Flux = Zero EMF

📚 Class XII – Physics Part I – Chapter: Electromagnetic Induction – Topic: Time Derivative of Flux

5 Choose the correct statements about multiple turn coils:
Statements
1. The induced emfs in each turn of a tightly wound coil add up in series.
2. N turns decrease the total induced emf by a factor of 1/N.
3. The total induced emf formula is ε = -N(dΦB/dt).
4. The flux through each turn is vastly different in a closely wound coil.

A (1), (3)

B (2), (4)

C (1), (2), (3)

D (3), (4)

💡 Short Explanation

�� Emfs add in series. �� EMF increases with turns. �� Same flux passes through turns.

✅ Correct Answer Explanation

Statement 1 is correct because individual turn emfs add. → Statement 3 is correct because: ε = -N(dΦ/dt) → Statement 2 is incorrect because increasing N increases emf. → Statement 4 is incorrect because closely wound coils experience nearly identical flux.

❓ Why Other Options Are Incorrect

�� Option B → Both statements are false.
�� Option C → Includes false Statement 2.
�� Option D → Includes false Statement 4.

🎯 Strategy

Used

�� Elimination

Application:

�� Check dependence of emf on N.

Final Logic:

�� More turns produce greater total emf.

🧠 Memory Trick

More Turns = More EMF

📚 Class XII – Physics Part I – Chapter: Electromagnetic Induction – Topic: Multiple Turn Coils

6 If the magnetic field Bi varies across different area elements dAi of a surface, the total magnetic flux ΦB is mathematically represented by the summation

A Σ (Bi · dAi)

B Σ (Bi × dAi)

C Σ (Bi / dAi)

D Σ (dAi / Bi)

💡 Short Explanation

�� Flux is a dot product. �� Sum contributions from all elements. �� Basis of surface integration.

✅ Correct Answer Explanation

Magnetic flux is defined as: Φ = ∫ B·dA → For discrete elements: Φ = Σ(Bi·dAi) → Therefore, Option A is correct.

❓ Why Other Options Are Incorrect

�� Option B → Cross product does not define flux.
�� Option C → No physical meaning.
�� Option D → Not a flux expression.

🎯 Strategy

Used

�� Conceptual Recall

Application:

�� Recall mathematical definition of magnetic flux.

Final Logic:

�� Flux is obtained using a dot product.

🧠 Memory Trick

Flux = B Dot A

📚 Class XII – Physics Part I – Chapter: Electromagnetic Induction – Topic: Magnetic Flux

7 When a current-carrying coil C₂ connected to a tapping key is placed near a stationary coil C₁,...

A a constant current in C₂ induces a steady current in C₁

B pressing the key induces a momentary current in C₁ due to the rapidly increasing magnetic field

C releasing the key has no effect on the magnetic flux through C₁

D inserting an iron core between the coils completely stops the flux change

💡 Short Explanation

�� Changing current changes magnetic flux. �� Induction occurs only during change. �� Mutual induction is involved.

✅ Correct Answer Explanation

When the key is pressed, current in C₂ rises from zero to a finite value. → This produces a rapidly changing magnetic field around C₂. → The changing magnetic flux linked with C₁ induces an emf and a momentary current. → Once the current becomes steady, the magnetic field becomes constant and induction stops. → Therefore Option B is correct.

❓ Why Other Options Are Incorrect

�� Option A → A constant current produces a constant magnetic field and no induced current.
�� Option C → Releasing the key decreases current and changes magnetic flux, producing induction.
�� Option D → An iron core increases flux linkage; it does not stop flux change.

🎯 Strategy

Used

�� Conceptual Recall

Application:

�� Apply the principle of mutual induction.

Final Logic:

�� Only changing current produces induced emf.

🧠 Memory Trick

Key Press = Flux Change

📚 Class XII – Physics Part I – Chapter: Electromagnetic Induction – Topic: Mutual Induction

8 A loop is situated in a magnetic field of 0.10 T. If it is shrunk such that its effective area perpendicular to the field decreases by 5.0 × 10⁻³ m² in 0.20 s, what is the magnitude of the induced emf?

A 2.5 × 10⁻³ V

B 1.0 × 10⁻⁴ V

C 2.5 × 10⁻⁴ V

D 5.0 × 10⁻³ V

💡 Short Explanation

�� Use Faraday's law. �� Flux change occurs due to area change. �� Direct substitution.

✅ Correct Answer Explanation

Given: B = 0.10 T ΔA = 5.0 × 10⁻³ m² Δt = 0.20 s → Since the field is perpendicular: ΔΦ = BΔA = (0.10)(5.0 × 10⁻³) = 5.0 × 10⁻⁴ Wb → Induced emf: ε = ΔΦ/Δt = (5.0 × 10⁻⁴)/(0.20) = 2.5 × 10⁻³ V → Therefore Option A is correct.

❓ Why Other Options Are Incorrect

�� Option B → Too small due to incorrect division.
�� Option C → One-tenth of correct value.
�� Option D → Twice the correct value.

🎯 Strategy

Used

�� Substitution

Application:

�� Apply ε = BΔA/Δt.

Final Logic:

�� ε = 2.5 × 10⁻³ V.

🧠 Memory Trick

Area Change ÷ Time = EMF

📚 Class XII – Physics Part I – Chapter: Electromagnetic Induction – Topic: Area Variation Method

9 Regarding rotating coils in fields, which one is correct?
Statements
1. Earth's steady magnetic field cannot induce an emf in a rotating coil.
2. The induced emf reaches its maximum magnitude when the rate of change of flux is zero.
3. Rotating a coil varies the angle θ, creating a time-varying flux.
4. The instantaneous induced emf is completely independent of the rotation speed.

A (1)

B (2)

C (3)

D (4)

💡 Short Explanation

�� Rotation changes θ. �� Flux becomes time-dependent. �� Induced emf is produced.

✅ Correct Answer Explanation

For a rotating coil: Φ = BA cosθ → Rotation continuously changes θ. → Therefore magnetic flux changes with time. → A changing flux induces emf. → Hence Statement 3 is correct.

❓ Why Other Options Are Incorrect

�� Option A→ A rotating coil in Earth's field can induce emf.
�� Option B→ Maximum emf occurs when rate of change of flux is maximum.
�� Option D→ Emf depends directly on angular speed.

🎯 Strategy

Used

�� Elimination

Application:

�� Evaluate the effect of rotation on magnetic flux.

Final Logic:

�� Rotation changes θ, causing induction.

🧠 Memory Trick

Rotate → Flux Changes

📚 Class XII – Physics Part I – Chapter: Electromagnetic Induction – Topic: Rotating Coils

10 For a coil placed in a uniform magnetic field, magnetic flux is given by:
Φ = BA cos θ
If B and A remain constant, what are the values of magnetic flux when the angle θ changes from 0° to 180°?

A Flux is +BA, Flux is -BA

B Flux is 0, Flux is BA

C Flux is -BA, Flux is +BA

D Flux is BA, Flux is 0

💡 Short Explanation

�� Flux depends on cosθ. �� cos0° = 1. �� cos180° = −1.

✅ Correct Answer Explanation

Magnetic flux: Φ = BA cosθ → At θ = 0°: Φ = BA cos0° = +BA → At θ = 180°: Φ = BA cos180° = −BA → Therefore, Option A is correct.

❓ Why Other Options Are Incorrect

�� Option B → Flux is not zero at θ = 0°.
�� Option C → Reverses initial and final values.
�� Option D → Flux at 180° is −BA, not zero.

🎯 Strategy

Used

�� Substitution

Application:

�� Substitute angle values into Φ = BA cosθ.

Final Logic:

�� Flux changes from +BA to −BA.

🧠 Memory Trick

0° = +BA, 180° = −BA

📚 Class XII – Physics Part I – Chapter: Electromagnetic Induction – Topic: Angle Dependence of Magnetic Flux

11 Match List I with List II regarding Lenz's law

List I	List II
(1) Polarity of induced emf	(a) 1834
(2) Open circuit in changing flux	(b) Opposes the change in magnetic flux
(3) Negative sign in Faraday's law	(c) Emf is induced but no current flows
(4) Lenz's law deduction year	(d) Represents Lenz's law mathematically

A 1-b, 2-c, 3-d, 4-a

B 1-a, 2-b, 3-c, 4-d

C 1-d, 2-c, 3-b, 4-a

D 1-c, 2-a, 3-d, 4-b

💡 Short Explanation

Lenz's law determines the polarity of the induced emf. An open circuit can have induced emf without current. The negative sign in Faraday's law represents opposition to flux change. Lenz proposed his law in 1834.

✅ Correct Answer Explanation

(1) Polarity of induced emf According to Lenz's law, the induced emf always acts to oppose the change in magnetic flux producing it. → 1 → b → (2) Open circuit in changing flux Even though magnetic flux changes and an emf is induced, the circuit is open, so no current can flow. → 2 → c → (3) Negative sign in Faraday's law Faraday's law is: ε = − dΦ/dt The negative sign mathematically represents Lenz's law. → 3 → d → (4) Lenz's law deduction year Lenz proposed the law in 1834. → 4 → a Therefore: 1 → b 2 → c 3 → d 4 → a Hence, Option A is correct.

❓ Why Other Options Are Incorrect

Option B: Incorrectly matches polarity with the year 1834 and misassigns other concepts.
Option C: Confuses polarity with the mathematical representation of Lenz's law.
Option D: Incorrectly associates an open circuit with the year 1834.

🎯 Strategy

Used

Matching Logic

Application:

Associate each concept with its precise physical meaning and historical fact.

Final Logic:

Polarity → Opposes flux change.
Open circuit → EMF without current.
Negative sign → Mathematical form of Lenz's law.
1834 → Year of Lenz's law.

🧠 Memory Trick

"Negative Sign = Opposition Sign"

📚 Topic: Lenz's Law and Polarity of Induced EMF.

12 Identify the correct statements regarding the direction of induced current according to Lenz's law.
(1) Current direction depends on whether flux is increasing or decreasing.
(2) Current flows counter-clockwise to oppose a North pole approaching.
(3) Current flows clockwise to oppose a North pole withdrawing.
(4) Induced current direction always aligns to increase the original magnetic field.

A 1, 2, 3

B 2, 3, 4

C 1, 3, 4

D 1, 2, 3

💡 Short Explanation

�� Current direction depends on flux change. �� Approaching and receding magnets produce opposite currents. �� Lenz's law opposes change.

✅ Correct Answer Explanation

(1) Correct — direction depends on increasing or decreasing flux. (2) Correct — an approaching North pole is opposed by creating a North face, requiring counter-clockwise current. (3) Correct — withdrawing North pole is opposed by creating a South face, requiring clockwise current. (4) Incorrect — induced field opposes flux change, not necessarily increases the original field.

❓ Why Other Options Are Incorrect

�� Option 2 → Includes incorrect statement 4.
�� Option C → Includes incorrect statement 4.
�� Option D → Includes incorrect statement 4.

🎯 Strategy

Used

Elimination

Application:

Reject statements violating Lenz's law.

Final Logic:

Induced current always opposes the flux variation.

🧠 Memory Trick

Oppose the Change

📚 Class XII – Physics Part I – Chapter: Electromagnetic Induction – Topic: Direction of Induced Current

13 Which of the following statement about Lenz's law and the induced magnetic effects that counter changes in magnetic flux is incorrect?

A An increasing flux through a loop induces a current that creates opposing flux.

B A decreasing flux through a loop induces a current that creates supporting flux.

C The magnetic moment of the induced current always points parallel to the changing external field.

D Lenz's law dictates that the induced effect always attempts to counter the original flux variation.

💡 Short Explanation

�� Magnetic moment may be parallel or antiparallel. �� It depends on flux change. �� Lenz's law opposes the change.

✅ Correct Answer Explanation

The induced magnetic moment is determined by the need to oppose the change in flux. It may be parallel or antiparallel depending on whether flux is increasing or decreasing. Therefore statement C is incorrect.

❓ Why Other Options Are Incorrect

�� Option A → Correct application of Lenz's law.
�� Option B → Correct because induced field supports decreasing flux.
�� Option D → Fundamental statement of Lenz's law.

🎯 Strategy

Used

Extreme Word Filter

Application:

The word "always" often signals an incorrect statement.

Final Logic:

Magnetic moment direction depends on the nature of flux change.

🧠 Memory Trick

Increase → Oppose, Decrease → Support

📚 Class XII – Physics Part I – Chapter: Electromagnetic Induction – Topic: Opposition Principle

14 Choose the correct statements about magnetic polarity of coils
(1) A coil facing an approaching North pole develops a North polarity.
(2) The developed North polarity causes an attractive force on the magnet.
(3) A receding North pole induces a South polarity on the facing side of the coil.
(4) The induced polarities act to accelerate the magnet's motion naturally.

A (1), (3)

B (2), (4)

C (1), (2)

D (3), (4)

💡 Short Explanation

�� Approaching North pole → induced North pole. �� Receding North pole → induced South pole. �� Induced force opposes motion.

✅ Correct Answer Explanation

(1) Correct — approaching North pole is opposed by forming a North pole. (3) Correct — receding North pole is opposed by forming a South pole. (2) Incorrect — North-North interaction is repulsive. (4) Incorrect — induced effects oppose motion rather than accelerate it.

❓ Why Other Options Are Incorrect

�� Option B → Both statements violate Lenz's law.
�� Option C → Contains incorrect statement 2.
�� Option D → Contains incorrect statement 4.

🎯 Strategy

Used

Elimination

Application:

Apply magnetic pole interaction and Lenz's law.

Final Logic:

Induced poles always resist the change producing them.

🧠 Memory Trick

Approach → Repel, Recede → Attract

📚 Class XII – Physics Part I – Chapter: Electromagnetic Induction – Topic: Magnetic Polarity by Lenz's Law

15 If the hypothetical scenario of a perpetual-motion machine were possible through electromagnetic induction where induced current supported flux change, the kinetic energy K of an approaching magnet after a gentle push would theoretically

A K → ∞

B K = 0

C K = constant

D K < 0

💡 Short Explanation

�� Supporting flux change would accelerate motion. �� Energy would be created without input. �� This violates conservation of energy.

✅ Correct Answer Explanation

If induced currents aided rather than opposed the motion, the magnet would gain kinetic energy continuously without external work. Its kinetic energy would keep increasing indefinitely, implying perpetual motion and violation of energy conservation. Hence K → ∞.

❓ Why Other Options Are Incorrect

�� Option B → Energy would not become zero.
�� Option C → Energy would continuously increase.
�� Option D → Kinetic energy cannot be negative.

🎯 Strategy

Used

Contextual/Tonal Matching

Application:

Analyze the hypothetical consequence of violating Lenz's law.

Final Logic:

Unlimited acceleration implies unlimited kinetic energy.

🧠 Memory Trick

No Lenz = Perpetual Motion

📚 Class XII – Physics Part I – Chapter: Electromagnetic Induction – Topic: Energy Conservation and Lenz's Law

16 The work done against the repulsive force between an approaching magnet and an induced current...

A demonstrates that induction is an energy-free process

B is the sole reason why induction violates energy conservation

C provides the energy that is dissipated as Joule heating in the coil

D is recovered entirely when the magnet is held stationary

💡 Short Explanation

�� Mechanical work supplies energy. �� Energy converts to electrical energy. �� Coil dissipates energy as heat.

✅ Correct Answer Explanation

The external agent moving the magnet performs work against the induced magnetic force. This mechanical work is converted into electrical energy and eventually dissipated as Joule heat in the coil. Hence option C is correct.

❓ Why Other Options Are Incorrect

�� Option A → Induction requires energy input.
�� Option B → Induction does not violate energy conservation.
�� Option D → Energy is dissipated, not fully recovered.

🎯 Strategy

Used

Energy Accounting

Application:

Trace the source and destination of energy.

Final Logic:

Mechanical work becomes electrical and thermal energy.

🧠 Memory Trick

Work In = Heat Out

📚 Class XII – Physics Part I – Chapter: Electromagnetic Induction – Topic: Work Done Against Induced Forces

17 If a person does 3.0 × 10⁻² J of work in moving a magnet, and the induced current in the 5.0 Ω closed coil lasts for 0.60 s, what is the estimated constant induced current assuming all work converts to Joule heating? (Using W = I²Rt)

A 1.0 × 10⁻¹ A

B 2.0 × 10⁻¹ A

C 1.0 × 10⁻² A

D 3.0 × 10⁻¹ A

💡 Short Explanation

�� Use W = I²Rt. �� Solve for I. �� Substitute values carefully.

✅ Correct Answer Explanation

W = I²Rt 3.0 × 10⁻² = I²(5)(0.60) 3.0 × 10⁻² = 3I² I² = 1.0 × 10⁻² I = 0.10 A Thus: I = 1.0 × 10⁻¹ A

❓ Why Other Options Are Incorrect

�� Option B → Gives four times larger power.
�� Option C → Too small by factor of 10.
�� Option D → Produces excessive energy.

🎯 Strategy

Used

Substitution

Application:

Insert values into Joule heating formula.

Final Logic:

Direct calculation gives 0.10 A.

🧠 Memory Trick

W = I²Rt

📚 Class XII – Physics Part I – Chapter: Electromagnetic Induction – Topic: Energy Conversion in Induction

18 In the context of mechanical to electrical conversion, which one is correct?
Choose correct:

A electrical energy can be generated without expending mechanical work

B an open circuit dissipates large amounts of Joule heating

C the energy spent by an external agent moving the magnet is precisely the source of electrical energy

D Lenz's law implies that mechanical energy is always destroyed during induction

💡 Short Explanation

�� Energy must come from somewhere. �� Mechanical work is the source. �� Energy is transformed, not destroyed.

✅ Correct Answer Explanation

In electromagnetic induction, the electrical energy generated originates from the mechanical work done by the external agent moving the magnet or conductor. This ensures conservation of energy.

❓ Why Other Options Are Incorrect

�� Option A → Violates conservation of energy.
�� Option B → Open circuit carries no current.
�� Option D → Energy is transformed, not destroyed.

🎯 Strategy

Used

Elimination

Application:

Remove statements violating conservation principles.

Final Logic:

Mechanical work is converted into electrical energy.

🧠 Memory Trick

Generator = Work → Electricity

📚 Class XII – Physics Part I – Chapter: Electromagnetic Induction – Topic: Mechanical to Electrical Energy Conversion

19 Rectangular loop moving out of uniform field into field-free region at constant velocity; Circular loop moving similarly:

A Constant induced emf, Variable induced emf

B Variable induced emf, Constant induced emf

C Constant induced emf, Constant induced emf

D Variable induced emf, Variable induced emf

💡 Short Explanation

�� Rectangular area decreases uniformly. �� Circular area decreases non-uniformly. �� Emf depends on rate of flux change.

✅ Correct Answer Explanation

For a rectangular loop moving out at constant speed, overlapping area decreases linearly with time. Hence: dΦ/dt is constant, giving constant emf. For a circular loop, the overlapping area changes nonlinearly, producing variable emf.

❓ Why Other Options Are Incorrect

�� Option B → Reverses the actual behavior.
�� Option C → Circular loop does not give constant emf.
�� Option D → Rectangular loop gives constant emf.

🎯 Strategy

Used

Geometrical Analysis

Application:

Examine how overlap area changes with time.

Final Logic:

Linear area change gives constant emf.

🧠 Memory Trick

Rectangle → Uniform Loss

📚 Class XII – Physics Part I – Chapter: Electromagnetic Induction – Topic: Moving Loops in Magnetic Fields

20 Match List I with List II for moving loops in a magnetic field

List I	List II
(1) Rectangular loop moving out of field	(a) Induced current opposes decreasing flux
(2) Triangular loop moving out of field	(b) No induced current exists
(3) Loop completely inside uniform field	(c) Rate of change of area is constant
(4) Irregular loop moving out of field	(d) Rate of change of area is variable

A 1-c, 2-d, 3-b, 4-a

B 1-a, 2-b, 3-c, 4-d

C 1-d, 2-c, 3-a, 4-b

D 1-b, 2-a, 3-d, 4-c

💡 Short Explanation

A rectangular loop loses area uniformly while leaving the field. A triangular loop loses area non-uniformly. A loop entirely inside a uniform magnetic field experiences no flux change. An irregular loop moving out of the field experiences decreasing flux, inducing current.

✅ Correct Answer Explanation

(1) Rectangular loop moving out of field The area inside the magnetic field decreases uniformly with time. Therefore, the rate of change of area is constant. → 1 → c → (2) Triangular loop moving out of field The area inside the field changes non-uniformly as the loop exits. Therefore, the rate of change of area is variable. → 2 → d → (3) Loop completely inside uniform field The magnetic flux remains constant because both the field and enclosed area remain unchanged. Hence, no induced current exists. → 3 → b → (4) Irregular loop moving out of field The magnetic flux decreases as the loop leaves the field. According to Lenz's law, the induced current opposes this decrease. → 4 → a Therefore: 1 → c 2 → d 3 → b 4 → a Hence, Option A is correct.

❓ Why Other Options Are Incorrect

Option B: Incorrectly assigns no induction to the triangular loop and constant area change to the loop inside the field.
Option C: A loop completely inside a uniform field cannot have induced current.
Option D: A rectangular loop moving out of the field does not correspond to no induction.

🎯 Strategy

Used

Matching Logic

Application:

Analyze how the area enclosed within the magnetic field changes for different loop geometries.

Final Logic:

Rectangle → Constant area loss.
Triangle → Variable area loss.
Uniform field with no flux change → No induction.
Decreasing flux → Current opposes the decrease.

🧠 Memory Trick

"No Flux Change = No Current"

📚 Topic: Flux Change Due to Motion of Loops in a Magnetic Field.

CUET UG Physics Booster Test 3-Faraday’s Laws and Lenz’s Law

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