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1 markRadioactivity

CAPE Physics Unit 2 · 2018 · Paper 2 · Question 3(b)(ii)

An investigation provides elapsed time and count rate data for a radioactive isotope in Table 3.

Draw the tangent to the curve at the point where t = 0 and produce the tangent to intersect the t-axis.

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Other parts of this question

  1. 3(a)(i)Write the exponential decay equation for radioactive materials.[1 mark]
  2. 3(a)(ii)Identify the decay constant in the equation in (a)(i) and state the units in which it is usually quoted.[2 marks]
  3. 3(b)(i)On the grid provided in Figure 4, plot a graph of count rate versus elapsed time, and draw a best smooth curve through the points.[3 marks]
  4. 3(b)(iii)Read off the value of t at the point of intersection.[1 mark]
  5. 3(c)It can be shown that the half-life is 0.69τ where τ is the value of t at the point of intersection with the tangent. Calculate the half-life using this formula.[1 mark]
  6. 3(d)Determine the half-life by directly reading off from your graph and suggest a reason for any discrepancy between this value and the value calculated in (c).[2 marks]
  7. 3(e)If the initial sample contained 50 grams of the radioisotope at the start of the experiment, determine the quantity remaining after 4 hours.[4 marks]

More practice: the rest of this paper · more Radioactivity questions · all CAPE Physics Unit 2 past papers