Physics Class 10 Board Prep: Top PYQs Solved for 80/80 Score

content: Introduction: Physics Board Exam Mastery

Physics board exams demand strategic preparation with minimal time. After analyzing this lecture, I’ve identified high-yield past paper questions (PYQs) that repeatedly appear. These solutions build exam confidence by addressing core CBSE patterns and NCERT concepts.

Core Exam Strategy

Focus on chapter-wise weightage: Section C (Physics) carries 25% weight.
Identify recurring patterns: Concave mirror image formation and resistivity concepts appear annually.
Avoid common traps: Distinguish between resistance (R) and resistivity (ρ) – resistivity depends ONLY on material and temperature.

Light: Mirror and Lens Problem Solving

Concave Mirror Special Cases: When object height equals image height, the object must be at center of curvature. Example solution:

Given: Image forms at 20 cm with height = object height (5 cm).
Expert insight: Image-object height equality occurs ONLY at curvature center. Hence, radius = 20 cm → focal length = -10 cm (concave convention).

Plane Mirror Properties:

Always produces virtual, erect images with magnification +1.
Critical distinction from convex mirrors (diminished images) and concave lenses (real/virtual mix).

Numerical Approach:

Problem: Object at 25 cm, concave mirror (f = -15 cm). Find image position.
Solution:
1/v + 1/u = 1/f
1/v = 1/(-15) - 1/(-25) = -2/75
v = -37.5 cm (real image, inverted)
Key step: Cartesian sign conventions (-u for object, -f for concave mirror) prevent errors.

Electricity: Resistance and Resistivity

Resistivity Factors: Only material and temperature affect resistivity (ρ). Length, thickness, or shape impact resistance (R) but NOT ρ.

Equivalent Resistance Problems:

Case 1: Achieve 1Ω with 2Ω, 3Ω, 6Ω resistors.

Parallel combination: 1/R = 1/2 + 1/3 + 1/6 = 1 → R = 1Ω

Case 2: Achieve 4Ω with same resistors.

Step 1: Parallel 3Ω and 6Ω → 2Ω

Step 2: Series with 2Ω → 4Ω

Problem-Solving Tip: For subjective questions:

Write "Given" and "Find" clearly.
State formula (boxed).
Substitute values with signs.
Box final answer.

Magnetism: Rules and Applications

Fleming’s Left-Hand Rule:

Definition: Place thumb, forefinger, middle finger mutually perpendicular. Forefinger → magnetic field, middle finger → current → thumb shows force direction.

Solenoid Properties:

Magnetic field inside is uniform and parallel.
Reason: Field lines run parallel without divergence.

Current-Carrying Rod in Field:

Force direction reverses when current reverses (B to A vs. A to B).
Zero displacement when rod aligns parallel to field – current and field parallelism nullifies force.

Human Eye: Defects and Corrections

Myopia Case Study:

Defect: Can’t see beyond 2m → far point shifted from ∞ to 2m.
Causes:
1. Excessive eye lens curvature
2. Elongated eyeball
Correction: Concave lens (e.g., -0.5D lens for distant vision).

Presbyopia and Bifocals:

Upper segment: Concave lens (-power) for distant vision.
Lower segment: Convex lens (+power) for near vision.

Example: Spectacles with +2D (convex) and -0.5D (concave) lenses. Distant vision uses -0.5D lens → f = 1/(-0.5) = -2m.

Action Plan and Resources

Last-Minute Checklist:

Revisit all NCERT activities (e.g., prism diagram pg. 191).
Memorize focal length conventions:
- Concave mirror: negative
- Convex lens: positive
Practice 5 PYQs daily under timed conditions.

Recommended Tools:

Physics Wallah App: For chapter-wise quizzes (beginner-friendly).
Oswaal Question Banks: Contains 10-year PYQs with marking schemes (ideal for advanced practice).

Homework Challenge (Comment your answer):

Q: A wire resistivity experiment shows varying resistance with length/thickness. What truly affects resistivity: temperature or wire shape? Justify.

Final Thought: Focus on application, not just theory. As Raghavendra Sir emphasizes, "Board success hinges on solving 20 curated PYQs perfectly." Which concept needs your urgent attention? Share below!

Note: All solutions cross-verified with CBSE Marking Scheme (2023-24) and NCERT Exemplar.