Answering "Show That" Questions

"Show that" questions are a distinctive feature of physics exams. Unlike standard calculations where you work towards an unknown answer, in a "show that" question you are given the answer and your job is to prove it through clear, logical working. These questions are common across all three Edexcel papers and appear frequently in mechanics, fields, waves, and energy calculations.

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What Makes "Show That" Different

In a standard calculation, you work from known values to find an unknown. In a "show that" question, the answer is provided — but this does not make it easier. In fact, many students find these questions harder because:

1. You cannot work backwards. Examiners can tell when a student has started from the given answer and reverse-engineered the working. This approach often earns zero marks even if the arithmetic appears correct.
2. Every step must be shown. You cannot skip steps that would be acceptable in a normal calculation.
3. You must show more precision. Your final answer should have at least one more significant figure than the given answer.

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The Correct Approach

Follow this process for every "show that" question:

Step 1: Identify the relevant physics