Physics

Problem

A primary coil

P

is closely coupled to two identical secondary coils

S_1

and

S_2

wound on the same core. The coils

S_1

and

S_2

are connected in series so that their induced emfs add. Mutual inductances are

M_1 = 0.10\,\text{H}

for

P

with

S_1

and

M_2 = 0.15\,\text{H}

for

P

with

S_2

. The current in

P

varies as

I_p = 5e^{-20t}\,\text{A}

(

t

in seconds). Determine the emf across the series combination of

S_1

and

S_2

t = 0

. a)

+15\,\text{V}

+25\,\text{V}

+5\,\text{V}

-25\,\text{V}