A radioactive substance initially measures 3 grams and has a half-life of 250 years. Find a formula for the amount of substance left in grams after t years.

Respuesta :

Answer:

[tex]\bf\displaystyle N=3\cdot \left(\frac{1}{2} \right)^{\frac{t}{250} }[/tex]

Explanation:

Half-life means the time require for a radioactive to have half of its particles disintegrated. Therefore it forms a geometric sequence with:

  • the 1st Term (Uā‚) = initial number of particles
  • ratio (r) = [tex]\frac{1}{2}[/tex]
  • n = multiple of half-life

Therefore, the general formula for the amount left:

[tex]\boxed{N=N_o\cdot \left(\frac{1}{2} \right)^n}[/tex]

where:

  • N = amount left
  • Nā‚€ = initial amount
  • n = multiple of half-life

For t years, it has a multiple of half-life:

[tex]\boxed{n=\frac{t}{T} }[/tex] where, T = half-life

Therefore, we can also write the formula as:

[tex]\boxed{N=N_o\cdot \left(\frac{1}{2} \right)^{\frac{t}{T} }}[/tex]

Now, we can find the formula by substituting the given data:

[tex]\displaystyle N=N_o\cdot \left(\frac{1}{2} \right)^{\frac{t}{T} }[/tex]

[tex]\bf\displaystyle N=3\cdot \left(\frac{1}{2} \right)^{\frac{t}{250} }[/tex]