Question

Ten years ago, the magnitude of the electric field of the electromagnetic waves produced by a particular microwave oven was E_o. Today, the oven outputs only half the electric field (in amplitude) it used to. The amount of time it takes to cook things in the microwave is proportional to the intensity of the waves. How much longer does it take to cook things in this microwave oven now, compared with the time it took 10 years ago? HINT: Think about how the electric field amplitude is related to intensity, and think about whether you expect the cooking time to be longer or shorter after 10 years.

- twice as long

- half the time   

-four times as long

-one fourth the time

Answer 1

The intensity of the Electromagnetic waves is proportional to square of the amplitude of the electric field.

where Eo is the amplitude of the electric field.

As the amount of time, it takes to cook things in the microwave is proportional to the intensity of the waves and now the output of the electric field in amplitude is half as 10 years ago.

So cooking time will four-times as long compared to 10 years ago because intensity will be one fourth as 10 ten years ago.

Thus 3rd option four-times as long is correct.