JEE Main Alternating Current PYQ

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16. (AIEEE 2006)

In an $A C$ generator, a coil with $N$ turns, all of the same area $A$ and total resistance $R,$ rotates with frequency $ω$ in a magnetic field $B .$ The maximum value of $e m f$ generated in the coil is

A. $N . A . B . R .$ $ω$

B. $N . A . B$

C. $N . A . B . R .$

D. $N . A . B .$ $ω$

Correct Option is (D)

$e = - \frac{d ϕ}{d t} = - \frac{d (N \vec{B} . \vec{A})}{d t}$

$= - N \frac{d}{d t} (B A \cos ω t) = N B A ω \sin ω t$

$\Rightarrow e_{max} = N B A ω$

17. (AIEEE 2004)

Alternating current can not be measured by $D . C .$ ammeter because

A. Average value of current for complete cycle is zero

B. $A . C .$ Changes direction

C. $A . C .$ can not pass through $D . C .$ Ammeter

D. $D . C .$ Ammeter will get damaged.

Correct Option is (A)

$D . C .$ ammeter measure average current in $A C$ current, average current is zero for complete cycle. Hence reading will be zero.