Homework Help: physics

Posted by physics on Saturday, March 14, 2009 at 10:57am.

please check these:
Which interaction of nature binds atoms and molecules by attracting unlike charges and repulsing like charges?
a. strong b. weak c. electromagnetic d. gravitational
i got A, but someone said C , so i just want to make sure

How is a motor's mechanical energy able to perform mechancical work?
a. mechanical energy is converted into electrical energy
b. a current is generated by a rotating loop in a magnetic field
c. electrical energy is ocnverted into a magnetic force
d. a shaft connected to the rotating coil is attached to some external force

D

the rms current in an ac current is 3.6A. Find the maximum current

5.1 A

Which of the following statements about electromagnetic radiation is true?
a. it transfers energy to objects in the path of the electromagnetic waves
b. it can be converted to other energy forms
c. it transports the enrgy of electromagnetic waves
d. all of the above

B

What causes the dark lines in the absorption spectrum of an element to occur?
a. photons are absorbed when electrons jump from a higher-energy to a lower-energy state
b. photons are emitted when electrons jump from a higher-energy to a lower-energy state
c. photons are absorbed when electrons jump from a lower-energy to a higher-energy state
d. photons are emitted when electrons jump from a lower-energy to a higher-energy state

C

thanks!

physics - GanonTEK, Saturday, March 14, 2009 at 11:32am
Force is C - Electromagnetic
The Strong force binds gluons inside protons and neutrons

Yes, I think D is right for the mechanical force one.

Yes 5.1

I think it's D - All of the above
Here is an example
a - UV radiation causes sunburn
b - UV radiation is used by Solar panels
and it does transport the energy.

Does that make sense?

And finally C is correct.
It's not B and D anyway as an emitted photon would make some light and it's not A as going from higher to lower releases energy
physics - physics, Saturday, March 14, 2009 at 11:35am
ok, thanks...i just want few other people to reply to this post...just to be sure
i agree with you but int the one "which of the following statements about electromagenetic..."
i'm not sure between B and D
thanks again
physics - GanonTEK, Saturday, March 14, 2009 at 11:54am
I'm fairly certain it's D i'll explain my reasons again - hope fully better :)

Ok, my example is going to be UV radiation from the sun.

a. it transfers energy to objects in the path of the electromagnetic waves

When you are outside in the sun UV radiation is, for lack of a better word, hitting you your skin absorbs the energy and gets hotter causing the skin to eventually burn - tanning then sunburn. So that proves 'a'.

b. it can be converted to other energy forms

When UV light falls on a solar panel the radiation is converted into electrical energy which can be used to heat water for example or power lights.
Solar lights are another example - they absorb UV and light and convert it to electrical energy too.

I hope that makes sense.

c. it transports the energy of electromagnetic waves

Energy is transferred in one of 3 ways - conduction, convection and radiation.
Conduction is what occurs if you touch a hot coal. [solids touching]

Convection is what heats a room when radiator is on. [A radiator should actually be called a convector as it does not radiate energy.] [heated gases usually]

Radiation is what heats the earth, for example. Electromagnetic radiation transferring energy.

The earth is surrounded by nothing really - no gases to heat the earth by convection or hot solids touching the earth and giving energy by conduction.
It's radiation from the sun that makes the earth warm.

I hope that makes more sense!

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