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QLDPhysicsQuick questions
Unit 1: Thermal, nuclear and electrical physics
Quick questions on Half-life and exponential radioactive decay (QCE Physics Unit 1)
8short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is the activity after $24$ days?Show answer
($T_{1/2} = 8.0$ days.)
What is treating decay as linear?Show answer
Half of the remaining sample decays each half-life, not half of the original. After $2$ half-lives, $25\%$ remains, not $0\%$.
What is mixing units of time?Show answer
If $T_{1/2}$ is in days and $t$ is in seconds, the ratio is nonsense. Convert before substituting.
What is using natural log in the wrong direction?Show answer
$\lambda = \ln 2 / T_{1/2}$, not $T_{1/2} / \ln 2$.
What is treating activity as constant?Show answer
Activity drops exponentially along with $N$. The activity now is much smaller than the activity at $t = 0$.
What is iA1 data test?Show answer
Often a decay curve to read (activity vs time), with a half-life to extract and a future activity to predict.
What is eA Paper 1?Show answer
Multiple choice on $(1/2)^n$ for integer $n$.
What is eA Paper 2?Show answer
A two-part calculation: convert $T_{1/2}$ to $\lambda$, then find activity or number remaining at a non-integer number of half-lives using the exponential formula.