10 Common Mistakes in A-Level Physics and How to Avoid Them

A-Level Physics is unforgiving when it comes to small errors. This guide identifies the most common mistakes and shows you exactly how to avoid them.

1. Not Converting Units Correctly

One of the most frequent errors in Physics exams is failing to convert units properly. Questions often give measurements in different units (like mm and meters, or minutes and seconds), and forgetting to convert loses easy marks.

How to Avoid This:

• Always write down the given values with their units
• Convert everything to SI units (meters, kilograms, seconds) before calculating
• Circle or highlight units in different formats in the question
• Double-check your final answer units make sense

2. Significant Figures Errors

Questions often specify "give your answer to 2 significant figures" or similar. Missing this instruction or rounding incorrectly costs marks, even if your calculation is perfect.

How to Avoid This:

• Highlight the required precision when reading the question
• Keep full precision during calculations; only round the final answer
• If no precision is specified, use 2 or 3 significant figures
• Check your answer looks sensible (e.g., 0.003 not 0.0)

3. Forgetting to Show Working

Even if your final answer is wrong, you can earn method marks by showing clear working. Students who jump straight to answers lose these valuable marks when they make calculation errors.

How to Avoid This:

• Write down the equation you're using
• Show substitution of values with units
• Display each step of calculation separately
• Never do complex calculations in your head

4. Sign Errors in Vector Problems

Direction matters in Physics. Forgetting negative signs for vectors pointing in opposite directions or downward acceleration leads to incorrect answers in kinematics and forces questions.

How to Avoid This:

• Define a positive direction at the start (e.g., "taking up as positive")
• Draw a diagram showing all vectors with arrows
• Be consistent with your chosen direction throughout
• Check final velocity/acceleration directions make physical sense

5. Confusing Similar Concepts

Physics has many paired concepts that students mix up: distance vs displacement, speed vs velocity, mass vs weight, EMF vs potential difference, power vs energy.

How to Avoid This:

• Learn the precise definition of each term
• Create comparison tables for similar concepts
• Practice questions specifically testing these distinctions
• Read questions carefully—they're written precisely

6. Not Resolving Forces Correctly

In mechanics questions involving inclined planes or multiple force angles, students often forget to resolve forces into perpendicular components or do it incorrectly.

How to Avoid This:

• Always draw a force diagram first
• Resolve forces perpendicular to the plane of motion separately
• Use F cos θ for the component parallel to something at angle θ
• Use F sin θ for the component perpendicular to it
• Check both components separately before combining

7. Misreading Graph Axes

Velocity-time graphs, displacement-time graphs, and other plots have specific meanings. Students often confuse what the gradient or area represents.

How to Avoid This:

• Always read axis labels carefully
• Remember: gradient = y-axis ÷ x-axis
• For v-t graphs: gradient = acceleration, area = displacement
• For s-t graphs: gradient = velocity
• Practice interpreting different graph types regularly

8. Incorrect Rearrangement of Equations

Algebraic errors when rearranging physics equations are very common, especially with squared terms or when dealing with reciprocals.

How to Avoid This:

• Write the equation first before substituting numbers
• Rearrange algebraically before putting in values
• Check rearrangements by substituting back
• Be extra careful with 1/x terms and squared terms

9. Not Drawing Diagrams

Many students skip drawing diagrams for forces, circuits, or ray diagrams. This leads to missing information and conceptual errors.

How to Avoid This:

• Always draw a diagram even if not asked
• Label all quantities (forces, distances, angles)
• Use standard symbols for circuit components
• Make diagrams large enough to be clear

10. Forgetting Assumptions and Conditions

Physics equations often require specific conditions. Using SUVAT with non-constant acceleration or forgetting "in the absence of air resistance" leads to incorrect approaches.

How to Avoid This:

• Learn the conditions for each equation or law
• Check the question for stated conditions
• State assumptions you're making in your answer
• Look for key phrases like "constant acceleration" or "frictionless"

General Exam Strategy

Beyond these specific mistakes, follow these general principles:

• Read each question at least twice before starting
• Budget your time based on marks available
• Do easier questions first to build confidence
• If stuck, move on and return later
• Always write something—blank answers get zero marks
• Check answers for physical reasonableness

Practice Makes Perfect

The best way to avoid these mistakes is through extensive practice with past papers and topical questions. Use ExamWise to practice specific topics where you're prone to errors, and review mark schemes to understand exactly what examiners want.

Track the types of mistakes you make and consciously focus on avoiding them in future questions. Over time, you'll develop strong exam technique alongside your Physics knowledge.