Astudent has an 80 g sample of a radioactive material that has a half-life of 20 seconds. how much material will he have left after one minute?
a) 40 g
b) 1.33 g
c) 5 g
d) 10 g

= 10 g

Explanation:

Half life is the time taken by a radioactive substance to decay by half of the original mass or initial amount.

Therefore, to get the new mass after decay;

New mass = Original mass × (1/2)^n ; where n is the number of half lives.

n = 60 seconds/20 seconds

  = 3

Therefore;

New mass = 80 g × (1/2)^3

                   = 80 g × 1/8

                   = 10 g

when insulating materials rub against each other, they may become electrically charged . electrons , which are negatively charged, may be 'rubbed off' one material and on to the other. the material that gains electrons becomes negatively charged. the material that loses electrons is left with a positive charge.

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