MathematicsChapter 2: Logarithms
Light-Time Example
Distance 1.5 x 10^8 km divided by speed 3.0 x 10^5 km/s is (1.5/3.0) x 10^(8-5) = 0.5 x 10^3.
Learning objectives
- Define and explain light-time example.
- Apply light-time example to a focused FBISE question.
- Check the answer for correct terms, evidence, working, and units.
Definition
Distance 1.5 x 10^8 km divided by speed 3.0 x 10^5 km/s is (1.53.0) x 10(8-5) = 0.5 x 103. Rewrite 0.5 x 103 as 5 x 102, which is 500. So the time is 500 s. The same pattern works for any divide-then-adjust case.
Where / symbols
- Light-Time Example
- Distance 1.5 x 10^8 km divided by speed 3.0 x 10^5 km/s is (1.5/3.0) x 10^(8-5) = 0.5 x 10^3. Rewrite 0.5 x 10^3 as 5 x 10^2, which is 500. So the time is 500 s. The same pattern works for any divide-then-adjust case.
Overview
Learn the idea, then use it:
Core Understanding
Distance 1.5 x 10^8 km divided by speed 3.0 x 10^5 km/s is (1.53.0) x 10(8-5) = 0.5 x 103. Rewrite 0.5 x 103 as 5 x 102, which is 500. So the time is 500 s. The same pattern works for any divide-then-adjust case.
Examples 1.5 x 10^8 · 3.0 x 10^5 · 500 s · LIGHT-TIME EXAMPLE: Distance 1.5 x 10^8 km divided by speed 3.0 x 10^5 km/s is (1.5/3.0) x 10^(8-5) = 0.5 x 10^3. Rewrite 0.5 x 10^3 as 5 x
Exam Application
State the correct term, connect it to the chapter rule or evidence, and use a clear example or calculation.
Examples Define first · Show the rule or evidence · Check units, labels, and conclusion
WHAT — LIGHT-TIME EXAMPLE
Distance 1.5 x 10^8 km divided by speed 3.0 x 10^5 km/s is (1.53.0) x 10(8-5) = 0.5 x 103. Rewrite 0.5 x 103 as 5 x 102, which is 500. So the time is 500 s. The same pattern works for any divide-then-adjust case.
HOW — Use the idea
Identify what is given, select this topic's rule or evidence, apply it one step at a time, and check the result.
In simple words
Do not merge light-time example with a neighbouring idea that uses a different definition, rule, or method.
Key points
- 1.5 x 10^8
- 3.0 x 10^5
- 500 s
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Light-Time Example
Sticky Notes · Quick Revision
Core Idea
- Distance 1.5 x 10^8 km divided by speed 3.0 x 10^5 km/s is (1.53.0) x 10(8-5) = 0.5 x 103.
Key Points
- 1.5 x 10^8
- 3.0 x 10^5
- 500 s
Simple Check
- Explain light-time example in your own words and connect it to one chapter example.
How to Answer
- Define the idea, show the main rule or evidence, apply it, and check the final statement.
Common Mistake
- Do not merge light-time example with a neighbouring idea that uses a different definition, rule, or method.
FBISE Exam Tip
- Use the exact term, show working where needed, and include units or labelled evidence.
60-second revision
- Distance 1.5 x 108 km divided by speed 3.0 x 105 km/s is (1.53.0) x 10(8-5) = 0.5 x 103.
- 1.5 x 10^8
- 3.0 x 10^5
- 500 s
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