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1. (JEE Main 2024 (Online) 9th April Evening Shift )

A square loop of side 15   cm being moved towards right at a constant speed of 2   cm / s as shown in figure. The front edge enters the 50   cm wide magnetic field at t = 0 . The value of induced emf in the loop at t = 10   s will be :

JEE Main 2024 (Online) 9th April Evening Shift Physics - Electromagnetic Induction Question 4 English

A. zero

B. 4.5 mV

C. 0.3 mV

D. 3 mV

Correct Option is (A)

Time taken to cross the field region

= 50 2 = 25   s

At 10   s the loop is inside field and flux is not changing.

ε induced  = 0

2. (JEE Main 2024 (Online) 31st January Morning Shift )

A coil is places perpendicular to a magnetic field of 5000   T . When the field is changed to 3000   T in 2   s , an induced emf of 22   V is produced in the coil. If the diameter of the coil is 0.02   m , then the number of turns in the coil is:

A. 35

B. 70

C. 7

D. 140

Correct Option is (B)

ε = N ( Δ ϕ t ) Δ ϕ = ( Δ B ) A B i = 5000   T ,   B f = 3000   T   d = 0.02   m r = 0.01   m Δ ϕ = ( Δ B ) A = ( 2000 ) π ( 0.01 ) 2 = 0.2 π ε = N ( Δ ϕ t ) 22 = N ( 0.2 π 2 ) N = 70

3. (JEE Main 2024 (Online) 27th January Morning Shift )

A rectangular loop of length 2.5   m and width 2   m is placed at 60 to a magnetic field of 4   T . The loop is removed from the field in 10   sec . The average emf induced in the loop during this time is

A. -2V

B. +2V

C. +1V

D. -1V

Correct Option is (

According to Faraday's Law of Electromagnetic Induction, the induced emf in a closed circuit is equal to the negative rate of change of magnetic flux through the circuit. Mathematically, it is expressed as:

ε = d Φ d t

Where ε is the induced emf, and Φ is the magnetic flux.

To find the magnetic flux Φ through the rectangular loop, we use the formula:

Φ = B A cos ( θ )

Where:

  • B is the magnetic field strength,
  • A is the area of the loop, and
  • θ is the angle between the magnetic field lines and the normal (perpendicular) to the plane of the loop.

The area A of the rectangular loop is:

A = length × width = 2.5   m × 2   m = 5   m 2

Given the angle θ = 60 , we can calculate the initial magnetic flux Φ i n i t i a l :

Φ i n i t i a l = B A cos ( 60 )

Φ i n i t i a l = 4   T 5   m 2 cos ( 60 )

Φ i n i t i a l = 4 5 1 2 = 10   Wb

(Since cos ( 60 ) = 1 2 )

When the loop is removed from the magnetic field, the final magnetic flux Φ f i n a l is zero, because the loop is no longer within the magnetic field. Thus, the change in magnetic flux Δ Φ is:

Δ Φ = Φ f i n a l Φ i n i t i a l = 0 10   Wb = 10   Wb

The loop is removed from the field in t = 10 seconds, so the rate of change of magnetic flux is:

d Φ d t = Δ Φ Δ t = 10   Wb 10   s = 1   Wb / s

Now we can find the average induced emf ε :

ε = d Φ d t

ε = ( 1   Wb / s )

ε = + 1   V

Therefore, the average induced emf in the loop during this time is + 1   V . The correct answer is:

Option C

+ 1   V

)

4. (JEE Main 2024 (Online) 1st February Evening Shift)

A coil of 200 turns and area 0.20   m 2 is rotated at half a revolution per second and is placed in uniform magnetic field of 0.01   T perpendicular to axis of rotation of the coil. The maximum voltage generated in the coil is 2 π β volt. The value of β is _______.

Correct answer is 5

ϕ = NAB cos ( ω t ) ε = d ϕ dt = NAB ω sin ( ω t ) ε max = NAB ω = 200 × 0.2 × 0.01 × π = 4 π 10 = 2 π 5 volt

5 (JEE Main 2024 (Online) 31st January Evening Shift)

The magnetic flux ϕ (in weber) linked with a closed circuit of resistance 8 Ω varies with time (in seconds) as ϕ = 5 t 2 36 t + 1 . The induced current in the circuit at t = 2   s is __________ A.

Correct answer is 2

ε = ( d ϕ dt ) = 10 t 36  at  t = 2 , ε = 16   V i = ε R = 16 8 = 2   A