1.) Uranium 238 has a half life of 1.41 x 10^17 sec if the earth is 5.5 billion years old what fraction of the original uranium 238 that was on earth when it formed is left

2.) hydrogen emits red light at a wavelength of 656 nm if M = 2 what value of n does this wavelength represents?

3.) you want to use a converging lens to magnify that an object 3 times. the lens has a focal length of 10 cm where should it be placed