Question

Which of these is the most likely use of an electromagnetic wave which has frequency lesser than ultraviolet rays but greater than infrared radiations?

heat food safely
make objects visible to humans
transmit radio and cellular phone signals
detect the location of objects which emit heat

Answer 1

Frequency between infra-red and ultraviolet includes radiowaves, microwaves and visible light.

So radios and cellular phones use radiowaves, while we see with the aid of visible light.

Heating food safely might be done with microwaves.

Answer 2

So heat food safely?

Answer 3

What I have mentioned makes the top 3 options correct.

However, the last is also correct, depending on whether your teacher accepts blackbody radiation. Depending on how hot the object is, they will emit different proportions of the different frequencies of light. If you heat a metal, at first you won't see anything because the radiation is in the infrared range, but as you continue to heat, it becomes red hot then yellow and eventually blue. Some stars are so hot that they give off ultraviolet.

Answer 4

humm.. okay. Thanks!

Answer 5

Many people migrated from Location A after the dam was constructed. Which of these statements best explains why people avoided living in location A after the construction of the dam? The dam may have

caused floods which harmed the ecology and agriculture.
polluted the atmosphere by emitting harmful gases.
produced acid rains because of harmful chemical reactions.
made land infertile because of toxic gases released by the power plant.

Answer 6

Visible light lies between ultra-violet and infra-red radiation in the spectrum. Making objects visible to humans is the most likely use of visible light among the choices.

Answer 7

That was another anyone can help??

Answer 8

Thanks @kropot72

Answer 9

oh... i got it wrong. radiowaves have lower energy than infra red :V so only seeing is the answer. sorry

Answer 10

You're welcome :)

Answer 11

Its alright :)

Answer 12

power plants do not emit poison. so floods is the only option.

Answer 13

Why cant it be B or C though?

Answer 14

hydro stations do not rely on chemical reactions and thus do no emit harmful gases.

Answer 15

but why was there a powerplant in the back of the picture giving out smoke

Answer 16

these stations simply "drop" the water, converting gravitational potential energy into kinetic energy which turns the turbines, which have magnets. These magnets exert a magnetic force on the electrons in the circuit making them move... but you'll learn more about the relation between magnets and charges later on.

Answer 17

So are you sure it is the floods?

Answer 18

Those are cooling towers.
http://en.wikipedia.org/wiki/Cooling_tower

Answer 19

Wow thanks!!! you are smart!!! :):)