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21. (JEE Main 2022 (Online) 26th July Evening Shift)

In a coil of resistance 8 Ω , the magnetic flux due to an external magnetic field varies with time as ϕ = 2 3 ( 9 t 2 ) . The value of total heat produced in the coil, till the flux becomes zero, will be _____________ J .

Correct answer is 2

R = 8 Ω

ϕ = 2 3 ( 9 t 2 )

At t = 3 , ϕ = 0

ε = | d ϕ d t | = 4 3 t

H = 0 3 V 2 R d t = 0 3 1 8 × 16 9 t 2 d t

= 2 9 × ( t 3 3 ) 0 3 = 2 9 × 3 × 27 = 2 J

22. (JEE Main 2022 (Online) 25th July Evening Shift)

Magnetic flux (in weber) in a closed circuit of resistance 20 Ω varies with time t(s) at ϕ = 8t2 9t + 5. The magnitude of the induced current at t = 0.25 s will be ____________ mA.

Correct answer is 250

R = 20 Ω

ϕ = 8 t 2 9 t + 5

ε = | d ϕ d t | = | 16 t 9 | = | 16 ( 0.25 ) 9 | = 5

i = ε R = 5 20 = 0.25 A = 0.25 10 3 × 10 3 A = 250 m A

23. (JEE Main 2022 (Online) 24th June Evening Shift)

A circular coil of 1000 turns each with area 1m2 is rotated about its vertical diameter at the rate of one revolution per second in a uniform horizontal magnetic field of 0.07T. The maximum voltage generation will be ___________ V.

Correct answer is 440

V max = N A B ω

= 1000 × 1 × 0.07 × ( 2 π × 1 )

440 volts

24. (JEE Main 2021 (Online) 31st August Evening Shift )

A coil is placed in a magnetic field B as shown below :

JEE Main 2021 (Online) 31st August Evening Shift Physics - Electromagnetic Induction Question 56 English

A current is induced in the coil because B is :

A. Outward and decreasing with time

B. Parallel to the plane of coil and decreasing with time

C. Outward and increasing with time

D. Parallel to the plane of coil and increasing with time

Correct Option is (A)

B must not be parallel to the plane of coil for non zero flux and according to lenz law if B is outward it should be decreasing for anticlockwise induced current.

25. (JEE Main 2021 (Online) 27th August Morning Shift )

A bar magnet is passing through a conducting loop of radius R with velocity υ . The radius of the bar magnet is such that it just passes through the loop. The induced e.m.f. in the loop can be represented by the approximate curve :

JEE Main 2021 (Online) 27th August Morning Shift Physics - Electromagnetic Induction Question 60 English

A. JEE Main 2021 (Online) 27th August Morning Shift Physics - Electromagnetic Induction Question 60 English Option 1

B. JEE Main 2021 (Online) 27th August Morning Shift Physics - Electromagnetic Induction Question 60 English Option 2

C. JEE Main 2021 (Online) 27th August Morning Shift Physics - Electromagnetic Induction Question 60 English Option 3

D. JEE Main 2021 (Online) 27th August Morning Shift Physics - Electromagnetic Induction Question 60 English Option 4

Correct Option is (C)

JEE Main 2021 (Online) 27th August Morning Shift Physics - Electromagnetic Induction Question 60 English Explanation
When magnet passes through centre region of solenoid, no current / Emf is induced in loop.

While entering flux increases so negative induced emf

While leaving flux decreases so positive induced emf.