What is the half life of a substance that 2.5 grams left from 10 grams in 24 hours

Two friends at different locations want to communicate with each other by sending low energy signals. which of the following methods can they use to communicate? a) produce x-rays using colliding electrons and send them to radios, which capture sound b) send messages using infrared radiation, which travel in the form of waves c) send radio waves through intervening media like radio and television d) produce sound waves using microwaves from heated objects

What must occur for air masses to form fronts

What was bohr’s contribution to the planetary model