Dhaka Board HSC Physics 2nd Paper MCQ Solution 2025: Your Ultimate Guide
Let’s be honest: sitting in that exam hall, staring at a circuit diagram or a half-life problem, your heart rate spikes just a little. You’ve put in the hours, but the Dhaka Board HSC Physics 2nd Paper MCQ has a reputation for being a “brain-bender.”
Whether you are here to double-check your marks or you’re a future candidate looking for the “logic” behind the magic, this guide is your roadmap. At Teachingbd24.com, we believe that knowing the answer is good, but understanding the why is what gets you into BUET or Dhaka Medical College. Let’s dive into the 2025 Dhaka Board solutions with the precision of a laser.
Table of Contents
1. The Power of Current Electricity: Why Did My Resistance Change?
One of the most discussed questions in the 2025 set involved a $16\Omega$ wire. The board loves this because it tests two concepts at once: resistance and geometry.
The Scenario
You take a $16\Omega$ wire, snip it in half, and tie those halves together in parallel.
The Expert Breakdown
When you cut the wire, the resistance of each piece drops because resistance is directly proportional to length ($R \propto L$). Consequently, each piece becomes $8\Omega$. However, when you connect them in parallel, you create more “paths” for electricity, which slashes the total resistance even further.
Table 1: Resistance Transformation Logic
| Step | Action | Resulting Resistance |
| Initial | Full length wire | $16\Omega$ |
| Step 1 | Cut into 2 equal parts | $8\Omega$ each piece |
| Step 2 | Connect in Parallel | $4\Omega$ (Final Answer) |
Pro-Tip: If you had connected them in series instead, you’d be back at $16\Omega$. Always read the connection type carefully!
2. Modern Physics: Is That Rocket Shrinking?
Einstein’s Special Theory of Relativity often feels like science fiction, but for Dhaka Board candidates, it’s a standard math problem. Question 6 asked about a rocket whose length “decreases by 1%.”
The Conversational Logic
Imagine you are standing on Earth with a stopwatch. A rocket zooms past. To you, the rocket looks shorter than it actually is. This isn’t an optical illusion; it’s Length Contraction.
Because the length decreased by 1%, the observed length $L$ is $0.99$ of the original $L_0$.
$$L = L_0 \sqrt{1 – \frac{v^2}{c^2}}$$
By solving this, we find the velocity is roughly $0.141c$. In simpler terms, that rocket is moving at 14.1% of the speed of light!
3. Thermodynamics: The Secret to Staying Cool
Question 18 touched on a fundamental truth of the universe: Entropy. If you want to make water colder than its surroundings, you have to fight nature.
Why the 2nd Law of Thermodynamics?
Heat naturally flows from hot to cold. To reverse this—to pull heat out of cold water and dump it into a warmer room—you need an external power source (like your fridge’s compressor). This is why the Second Law of Thermodynamics is the correct anchor for this phenomenon.
Table 2: Quick Reference for Laws of Thermodynamics
| Law | Focus Point | Practical Example |
| Zeroth | Thermal Equilibrium | How a Thermometer works |
| First | Energy Conservation | Why a gas piston heats up |
| Second | Entropy & Heat Flow | Why refrigerators need electricity |
4. Case Study: The Photoelectric Effect (Questions 16-17)
Let’s look at a “High-Value” cluster from the exam. The 2025 paper featured a graph showing the relationship between frequency and kinetic energy.
The Problem
Many students get confused between Threshold Frequency and Work Function:
- The Threshold: The minimum “entry fee” (frequency) needed to kick an electron off the metal surface.
- The Work Function: The energy equivalent of that fee.
Case Study Analysis
In the 2025 Dhaka Board paper, the graph provided a specific intercept on the x-axis. Students who correctly identified this point as the threshold frequency ($f_0$) were able to calculate the work function ($\Phi$) using $\Phi = h f_0$.
Crucial Note: The slope of an $E_k$ vs $f$ graph is always Planck’s Constant ($h$)!
5. Nuclear Physics: Tracking the Decay of Tritium
Tritium (an isotope of Hydrogen) appeared in Question 8. With a half-life of 12.5 years, what happens to 1 gram after 25 years?
Shutterstock
The Simple Way to Think
- After 12.5 years (1st half-life): $0.5\text{ gm}$ remains.
- After another 12.5 years (total 25 years): Half of $0.5$ remains, which is $0.25\text{ gm}$.
This is exponential decay in its purest form. While the math is simple, the board uses it to see if you can manage time without overcomplicating the formula.
6. The “Gotcha” Questions: Small Details, Big Impact
Physics is a game of units. Question 25 focused on Current Density. Many students confuse Current ($A$) with Current Density ($J$). While Current is a scalar, Density is a vector representing current per unit area. Therefore, the unit is $A/m^2$ or $Am^{-2}$.
Table 3: Unit Traps to Avoid
| Physical Quantity | Common Wrong Unit | Correct Unit (SI) |
| Current Density | $Am$ | $Am^{-2}$ |
| Pointing Vector | $W/m$ | $W/m^2$ ($MT^{-3}$) |
| Magnetic Flux | $T$ | $Wb$ (Tesla is for Field) |
High-Performance Checklist for HSC Physics MCQs
Use this checklist to avoid “silly mistakes” in your reviews:
- [ ] Unit Check: Did I convert cm to m or grams to kg?
- [ ] Graph Axes: What is on the X-axis? (e.g., Is it $\lambda$ or $1/\lambda$?)
- [ ] Vector vs. Scalar: Does the question ask for magnitude only?
- [ ] Calculator Mode: Is my calculator in Degrees or Radians?
- [ ] The “Not” Filter: Did the question ask “Which is not correct?”
Authoritative Resources for Further Study
- HyperPhysics (Georgia State University): Explore Physics Concepts
- MIT OpenCourseWare: Advanced Physics Lectures
- NIST: Physical Measurement Laboratory
Final Thoughts: Moving Beyond the Paper
The Dhaka Board HSC Physics 2nd Paper MCQ 2025 was a fair but rigorous test. Physics isn’t about being a human calculator; it’s about seeing the patterns in the universe.
By analyzing these solutions, you are building the analytical mindset required for a career in engineering, research, or medicine. Keep practicing, keep questioning, and always look for the logic behind the numbers.
Stay tuned to Teachingbd24.com for the most accurate subject-wise solutions and admission guidelines!
