1
MCQ (Single Correct Answer)

JEE Main 2018 (Online) 16th April Morning Slot

A coil of cross-sectional area A having n turns is placed in a uniform magnetic field B. When it is rotated with an angular velocity $$\omega ,$$ the maxium e.m.f. induced in the coil will be:
A
3 nBA$$\omega $$
B
$${3 \over 2}$$ nBA$$\omega $$
C
nBA$$\omega $$
D
$${1 \over 2}$$ nBA$$\omega $$

Explanation

Flux in the coil, $$\phi $$ = nBA sin($$\omega $$t)

When n = no. of turns

$$\,\,\,\,\,\,\,\,\,\,\,\,\,\,$$ A = Area of coil

$$\,\,\,\,\,\,\,\,\,\,\,\,\,\,$$$$\omega $$ = angular speed

Induced emf,

$$\left| e \right| = {{d\phi } \over {dt}}$$

= nBA$$\omega $$ cos$$\omega $$t

$$\therefore\,\,\,$$ emax = nBA$$\omega $$
2
MCQ (Single Correct Answer)

JEE Main 2018 (Online) 16th April Morning Slot

A power transmission line feeds input power at 2300 V to a step down transformer with its primary windings having 4000 turns, giving the output power at 230 V. If the current in the primary of the transformer is 5 A, and its efficiency is 90%, the output current would be ;
A
50 A
B
45 A
C
25 A
D
20 A

Explanation

Efficiency n = 0.9 = $${{{P_s}} \over {{P_p}}}$$

as $$\,\,\,\,\,\,$$ P = VI

$$\therefore\,\,\,$$ Ps = 0.9 $$ \times $$ Pp

$$ \Rightarrow $$ $$\,\,\,\,$$ Vs Is = 0.9 $$ \times $$ Vp Ip

$$ \Rightarrow $$ $$\,\,\,\,$$ Is = $${{0.9 \times 2300 \times 5} \over {230}}$$

= $$\,\,\,\,$$ 45 A
3
MCQ (Single Correct Answer)

JEE Main 2018 (Online) 16th April Morning Slot

A plane electromagnetic wave of wavelength $$\lambda $$ has an intensity I. It is propagatting along the positive Y-direction. The allowed expressions for the electric and magnetic fields are givn by :
A
B
C
D
4
MCQ (Single Correct Answer)

JEE Main 2019 (Online) 9th January Evening Slot

A power transmission line feeds input power at 2300 V to a srep down transformer with its primary windings having 4000 turns. The output power is delivered at 230 V by the transformer. If the current in the primary of the transformer is 5A and its efficiency is 90%, the output current would be :
A
50 A
B
45 A
C
35 A
D
25 A

Explanation

Given,

Primary voltage (VP) = 2300 V

Primary current (IP) = 5A

Secondary voltage (VS) = 230 V

efficiency ($$\eta $$) = 90%

We know,

Efficiency ($$\eta $$) = $${{{\mathop{\rm Sec}\nolimits} ondary\,Power} \over {\Pr imary\,\,Power}}$$

$$ \therefore $$   $$\eta $$ = $${{{P_S}} \over {{P_P}}}$$ = $${{{V_S}\,{I_S}} \over {{V_P}\,{I_P}}}$$

$$ \Rightarrow $$   0.9 = $${{230 \times {{\rm I}_S}} \over {2300 \times 5}}$$

$$ \Rightarrow $$   I = 45 A

Questions Asked from Alternating Current and Electromagnetic Induction

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