Which of the following statements are true?
1. Electromagnetic waves must be propagated through
solid, liquid, or gas particles.
II. Electromagnetic waves are generated over a range of frequencies.
III. Electromagnetic waves do not require a medium through which to travel.
IV. All electromagnetic waves travel at the speed of light.
A.
I and IV only
B. I. II and IV only
c. II and IV only
(D.
ll and Ill only

Astudent pours 10.0 g of salt into a container of water and observes the amount of time it takes for the salt to dissolve. she then repeats the process using the same amounts of salt and water but this time she slowly stirs the mixture while it is dissolving. the student performs the experiment one more time but this time she stirs the mixture rapidly. the dependent variable in this experiment is: time for salt to dissolve speed of stirring amount of water mass of salt