Doubtify – JEE Ki Taiyaari, Simple Bhasha Mein

  🎬 Restitution ka Concept – Ekdum Easy! "Jab do objects takraate hain, to unke bounce back karne ki ability ko hi bolte hain Coefficient of Restitution!" ⚡ What is Coefficient of Restitution (e)? Formula: e = (Relative speed after collision) / (Relative speed before collision) It tells us how “bouncy” a collision is. Simple! 🧠 Important Points to Remember: 0 < e < 1 → Partially Elastic Collision (thoda bounce, thoda energy loss) e = 1 → Perfectly Elastic Collision (poora bounce, no energy loss) e = 0 → Perfectly Inelastic Collision (no bounce, objects stick together) 🧪 Real-Life Example: Let’s say a ball hits the ground : If e = 0.8 → Ball bounce karegi, par speed thodi kam hogi If e = 0 → Ball bilkul waapas nahi aayegi (stick to ground) ❗ Memory Trick (Easy Yaad Karne Ke Liye): e = After / Before Numerator = After collision Denominator = Before collision Bas itna yaad rakho! 📢 Conclusion: "Bounce kitna hoga?...

  ⚡ Newton’s Third Law of Motion “For every action, there is an equal and opposite reaction.” This is Newton’s Third Law — simple to hear, yet powerful in real life! 🧠 What It Means: Whenever one body exerts a force on another body, the second body simultaneously exerts a force equal in magnitude but opposite in direction on the first body. Key Points: Action = Force applied Reaction = Equal force in opposite direction Forces always occur in pairs They act on different objects , not the same one! 🧪 Real-Life Examples: 🚀 Rocket Launch: The rocket expels gases downward (action), and in return, it is pushed upward (reaction). 🚶 Walking: You push the ground backward with your foot (action), and the ground pushes you forward (reaction). 🔫 Gun Recoil: The bullet is fired forward (action), and the gun jerks backward (reaction). 🐦 Bird Flying: The bird pushes air down with its wings (action), and the air pushes it upward (reaction). ❗ Commo...

  🧠 Physics in Real Life: How to Find the Unknown Mass of a Cube Using Archimedes’ Principle

  ⚙️ de-Broglie Wavelength vs Time – Charged Sheet Problem | Doubtify JEE 📌 Question: An electron is released from rest near an infinite non-conducting sheet of uniform negative charge density (−σ) . The rate of change of de-Broglie wavelength associated with the electron varies inversely as the nᵗʰ power of time . 👉 Find the numerical value of n . 📸 Question Image:

  🔬 Bulk Modulus Concept – Find Initial Volume | Doubtify JEE 📌 Question: A sample of a liquid is kept at 1 atm . It is compressed to 5 atm , which leads to a change of volume of 0.8 cm³ . If the bulk modulus of the liquid is 2 GPa , the initial volume of the liquid was ______ litre . (Take 1 atm = 10⁵ Pa) 🖼️ Question Image:

  ⚙️ A Thin Rotating Disk – Torque & Diameter Problem | Doubtify JEE 📌 Question: A thin solid disk of mass 1 kg is rotating along its diameter axis at the speed of 1800 rpm . An external torque of 25π Nm is applied for 40 seconds , increasing the speed to 2100 rpm . Find the diameter of the disk. 📸 Question Image:

🚆 Train Crossing Concept in 59 Seconds | Doubtify JEE Shorts 📌 Question: Ever wondered how long one train takes to pass another or a platform? The Train Crossing Concept helps solve such questions in seconds using speed-distance fundamentals.

  🧲 Magnetic Field at Centre of Square Loop with Unequal Resistance | JEE Concept 📌 Question: Figure shows a current-carrying square loop ABCD of edge length ‘a’ lying in a plane. If the resistance of the path ABC is r and the path ADC is 2r, find the magnitude of the resultant magnetic field at the centre of the square loop. 🖼️ Question Image: 💡 Concept Used: Unequal resistance in different paths means current divides unequally in branches. Use current division rule and Biot-Savart Law or symmetry to find net magnetic field at center. Magnetic field due to a straight segment at center of square is: B = μ 0 I 4 π R ⋅ 2 sin ⁡ ( θ / 2 ) or use full loop formula if current is symmetrical. 🧠 Approach: Let total current be I. Since resistances are in parallel: Current in ABC: I 1 = 2 3 I I_1 = \frac{2}{3}I I 1 ​ = 3 2 ​ I Current in ADC: I 2 = 1 3 I I_2 = \frac{1}{3}I I 2 ​ = 3 1 ​ I Both paths form half-loops and contribute to B at center ....

  📌 Newton’s Law of Cooling – Explained for JEE | Formula + Graph + Example 🖼️ Image:

⚡ Gauss’s Law – Flux Through a Cube | JEE Physics | Doubtify 📌 Question: An infinitely long wire has uniform linear charge density λ = 2 nC/m. The net flux through a Gaussian cube of side length √3 cm, if the wire passes through any two corners of the cube, that are maximally displaced from each other, would be x Nm²C⁻¹, where x is: 🖼️ Question Image:

  🧪 Young’s Modulus from Wire Extension | JEE Physics | Doubtify 📌 Question: A 3 m long wire of radius 3 mm shows an extension of 0.1 mm when loaded vertically by a mass of 50 kg in an experiment to determine Young's modulus. The value of Young’s modulus of the wire as per this experiment is P × 10¹¹ N/m² , where the value of P is: (Take g = 3π m/s²) 🖼️ Question Image:

  🌊 Superposition of Two Harmonic Waves – Find Resultant Amplitude & Phase | JEE Physics | Doubtify 📌 Question: The amplitude and phase of a wave that is formed by the superposition of two harmonic travelling waves, y₁(x, t) = 4sin(kx − ωt) and y₂(x, t) = 2sin(kx − ωt + 2π/3) are: 🖼️ Question Image:

  🌈 YDSE with Red and Green Filters – Interference of Light | JEE Physics | Doubtify 📌 Question: In a Young's double slit experiment (YDSE) , the source is white light . One of the slits is covered by a red filter and the other by a green filter . What will be observed? Options: There shall be an interference pattern for red distinct from that for green. There shall be an interference pattern, where each fringe’s pattern center is green and outer edges is red. There shall be no interference fringes . There shall be alternate interference fringes of red and green. 🖼️ Question Image:

  🔥 Adiabatic Compression of Monatomic Gas | Thermodynamics | JEE Physics | Doubtify 📌 Question: A monatomic gas having γ = 5 3 \gamma = \frac{5}{3} ​ is stored in a thermally insulated container , and the gas is suddenly compressed to 1 8 th \frac{1}{8}^\text{th} of its initial volume. What is the ratio of final pressure to initial pressure ? 🖼️ Question Image:

  ⚡ Surface Charge Distribution on Irregular Conductor – Electrostatics | JEE Physics | Doubtify JEE 📌 Question: Electric charge is transferred to an irregular metallic disk as shown in the figure. If the surface charge densities at four points are σ₁, σ₂, σ₃, and σ₄ , then which of the following options is correct ?

  ⚡ Surface Charge Density After Contact – Electrostatics | JEE Physics | Doubtify JEE 📌 Question: Two metal spheres of radius R and 3R have the same surface charge density σ . They are brought in contact and then separated . After separation, let the surface charge densities be σ₁ (for smaller sphere) and σ₂ (for larger sphere). What is the ratio σ₁ / σ₂ ? 🖼️ Question Image:

  🏐 Momentum vs Height Graph – Vertical Motion | JEE Physics | Doubtify JEE 📌 Question: A ball is thrown vertically upwards (take +z-axis as upwards) from the ground. 👉 Which of the following momentum-height (p–h) graphs correctly represents the motion? This is a concept-based question that checks your understanding of vector momentum and energy conservation . 🖼️ Question Image:

  🚀 Uniform Acceleration Motion Graphs | Kinematics | Doubtify JEE 📌 Question: A particle starts from origin O from rest and moves with a uniform acceleration along the positive x-axis . 👉 Identify all the graphs that correctly represent the motion qualitatively: a = acceleration v = velocity x = displacement t = time This is a conceptual question testing your understanding of motion graphs! 🖼️ Question Image:

  🧭 Relative Motion of Ships – Minimum Distance Concept | JEE Physics | Doubtify JEE 📌 Question: Ship A is sailing towards north-east with velocity v = 30 î + 50 ĵ km/h , where î points east and ĵ points north . Ship B is at a distance of 80 km east and 150 km north of Ship A and is sailing west at 10 km/h . 🔍 Find the time at which Ship A is at minimum distance from Ship B. 🖼️ Question Image:

  🚆 Train Crossing Time Ratio – Relative Motion | Speed, Distance & Time | JEE Physics | Doubtify JEE 💡 Question: A passenger train of length 60 m travels at a speed of 80 km/hr . Another freight train of length 120 m travels at a speed of 30 km/hr . Find the ratio of times taken by the passenger train to completely cross the freight train when: (i) They are moving in the same direction , and (ii) They are moving in opposite directions . 🖼️ Question Image: