calculate the percent activity of the radioactive isotope iodine-131 remaining after 5 half-lives.

after 1^st half life 50% will decay away.

after 2^nd halflife only 25% of the original atom will remain

after another half-life only 12.5% of the original half-life will remain.

after 4^th half-life only  6.25% will remain

and after the 5^th half-life only the 3.125% will remain.

therefore after 5 halflifes only 3.125% of the original samle will remain

compared with a simple galvanometer, an electric motor is _________.

an electric motive detect magnetic field lines or (electric current).

is it correct to say that a transformer boosts electric energy? defend your answer.

no, transformer only step up or step down electrical voltages,  step up transformer increases electrical voltages while step down voltages decreases electrical voltages.

what is induced by the rapid alternation of a magnetic field?

electrical current.

what must change in order for electromagnetic induction to occur in a wire coil?

the mire or the magnetic bar must move  continuously perpendicularly  to the coil before  electromagnetic induction can occur.

who discovered electromagnetic induction, and who put it to practical use?

it was discovered by Michael faraday and put into practical use by fleming.