Carbon-14 is a radioactive isotope that occurs naturally - Edexcel - GCSE Physics - Question 4 - 2013 - Paper 1
Question 4
Carbon-14 is a radioactive isotope that occurs naturally.
Scientists use carbon-14 to help find the age of old pieces of wood.
This technique is called carbon datin... show full transcript
Worked Solution & Example Answer:Carbon-14 is a radioactive isotope that occurs naturally - Edexcel - GCSE Physics - Question 4 - 2013 - Paper 1
Step 1
Which of these describes half-life?
96%
114 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The correct answer is A: the time it takes for half of the undecayed nuclei to decay. This definition captures the essence of half-life in radioactive decay.
Step 2
Sketch a graph to show how the activity of a radioactive isotope changes with time.
99%
104 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The graph should show a downward curve that approaches zero over time, starting from point P. The y-axis represents activity, which decreases exponentially as time increases along the x-axis.
Step 3
Calculate the activity of the carbon-14 in the comb when it was new.
96%
101 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
To calculate the initial activity, we use the decay formula:
A_t = A_0 e^{- rac{t}{T_{1/2}}}
where:
At=0.55Bq (current activity)
t=11400years (time elapsed)
T1/2=5700years (half-life)
By rearranging and solving for A0, we find:
Explain why this is necessary to improve the accuracy of the investigation.
98%
120 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
Taking several readings of background radiation helps to average out any random fluctuations and ensure that the measurements are consistent. This is essential for accurately distinguishing the activity levels of the sample from ambient radiation.
Step 5
Suggest a reason for this change.
97%
117 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
Measuring the mass of undecayed carbon-14 is more reliable than measuring its activity, especially because old objects emit very low levels of radiation that can easily be confused with background radiation.
