Lesson: Chapter - 4

Half-Lives

In discussions of radioactivity, the half-life of an isotope refers to the time it takes for one-half of the sample to decay. If we start with 100 g of a radioactive substance whose half-life is 15 days, after 15 days 50 g of the substance will remain. After 30 days, 25 g will remain, and after 45 days, 12.5 g remains, and so on.

Example

A radioactive substance has a half-life of 20 minutes. If we begin with a 500 g sample, how much of the original sample remains after two hours?

Explanation

The easiest way to attack these questions is to start with the original amount of the sample, then draw arrows representing each half-life. Two hours is 120 minutes, so that’s six half-lives. At the end of the stated time period, 7.8 g remains. 500 g ? 250g ? 125g ? 62.5g ? 31.25g ? 15.625g ?7.8125g

Back Next

Next to display next topic in the chapter.

Practice Questions

Test Prep Lessons With Video Lessons and Explained MCQ

Large number of solved practice MCQ with explanations. Video Lessons and 10 Fully explained Grand/Full Tests.

Quantitative Aptitude Reasoning English General Knowledge Picture Patterns

Jobs in Pakistan Induction process Test Prep Sections Practice MCQs Admission Tests Test Sections Success on Tests Study in USA Pak Universities Employment ISSB Preliminaries Articles and Essays Schools & Colleges Study Abroad Career News

Arithmetic Geometry Data Interpretation Problem Solving Data Sufficiency Quant. Comparison

English Vocabulary English Correction Antonyms Synonyms Analogies Fill in the Blanks Critical Reading Text Completion

Number Series Picture Pattern Critical Reasoning Analytical Reasoning

Writing

Physics Chemistry Biology Mathematics Pak Penal Code Islamic Hudood Laws

Chemistry Strategies Chemistry Lessons Practice MCQs The Structure of Matter The States of Matter Reaction Types Stoichiometry Chemical Equilibrium and Reaction Rates Thermodynamics Descriptive Laboratory Basic Measurement and Calculation Review Chemical Formulas Review Nomenclature and Formula Writing Practice Tests

MCQ with question Explanations Scholarships and Financial Aid

Lesson: Chapter - 4

Half-Lives

Example

Explanation

Test Prep Lessons With Video Lessons and Explained MCQ

Current Menu

More for You

Develop English Vocabulary

Issue Analysis

Chemistry for Test Preparation

You may be interested in

Colleges in Lahore

Queen Mary College - Lahore

Admissions News and Info

USA Study Visa

PAF - Engineering

GRE Chemistry

LUMS - Business Degrees

Universities in Islamabad

About us

Quick Test Prep

Study Abroad

Lesson: Chapter - 4

Half-Lives

Example

Explanation

Test Prep Lessons With Video Lessons and Explained MCQ

Current Menu

Main Menu (Click/Tap to Open)

Current Menu

Quantitative

Verbal

Logical/Reasoning

Writing

Subjects

Chemistry

More for You

Develop English Vocabulary

Issue Analysis

Chemistry for Test Preparation

You may be interested in

About us

Quick Test Prep

Study Abroad