Year 10 Science · Unit 2 · Lesson 24

Radioactive Half-Life

Challenge Worksheet

Name
Date
Class

Learning Goals

Go Deeper

Find the mistakes

A student wrote these five statements in their revision notes

  1. "Half-life is the time it takes for all of the radioactive nuclei in a sample to decay."
  2. "After two half-lives, none of the original sample is left because half plus half makes a whole."
  3. "You can shorten an isotope's half-life by heating the sample or grinding it into a powder."
  4. "A 100 g sample with a half-life of 5 days will have 50 g left after 5 days and 0 g after 10 days."
  5. "Carbon-14 dating works because carbon-14 has a very short half-life of only a few days."

1. Identify the error in statement 1 and write the correct definition of half-life.

Challenge 1 mark

2. Correct statement 2. State the fraction of the original sample that actually remains after two half-lives, and explain why.

Challenge 1 mark

3. Correct statement 3. Explain what half-life actually depends on and why physical conditions do not change it.

Challenge 1 mark

Go Deeper (continued)

4. Correct statement 4. Work out how much of the 100 g sample is actually left after 10 days, showing your working.

Challenge 2 marks

5. Correct statement 5. State the approximate half-life of carbon-14 (146C) and explain why this value makes it useful for dating old objects.

Challenge 2 marks

Show What You Know

1. A sample of carbon-14 has decayed until only 1/16 of the original amount remains. Using a half-life of about 5730 years, calculate the approximate age of the sample. Show how many half-lives have passed and your full working.

Challenge 3 marks

Wrap Up

Why would an isotope with a half-life of a few hours be useless for dating a fossil thousands of years old? Explain in one or two sentences.

HSCScience · Year 10 Science · Unit 2 · Lesson 24 · Challenge Worksheet