Every Question
Answered.
Board exam questions from CBSE, ICSE, and all State Boards — answered with AI-structured explanations and community insights.
How does a capacitor store electric charge?
A 2 μF capacitor is connected to a 12 V battery. Calculate the electric charge stored on the plates of the capacitor when the switch is closed. Assume the capacitor behaves as an ideal capacitor. Also, explain why the capacitor does not allow the current to flow when the switch is closed.
Induction's Time-Domain Response?
Consider a long solenoid carrying a current of 2 A. Suddenly, the current is switched off. Describe and explain the nature of the induced electromotive force (e.m.f.) in the solenoid as a function of time, assuming the magnetic flux through the solenoid is 0.02 Wb.
Capacitance of a Parallel-Plate Capacitor?
A parallel-plate capacitor is made of two plates, each 5 cm x 10 cm in size, separated by a 2 mm thick dielectric material. The plates are 1 cm apart when empty. How will the capacitance change if the gap between the plates is reduced to 1 mm and the dielectric material is replaced with a different one of double the dielectric constant?
What determines the stability of a binary star system?
A binary star system consists of two stars orbiting each other. One of the stars is a red giant, while the other is a hot, white dwarf. Considering their masses and radii, will this system be stable in the long run, or will it eventually lead to a catastrophic collision?
Magnetic Field of a Current Carrying Wire?
A long, straight wire carries a current of 20 A in a direction perpendicular to the plane of the paper. Two identical loops, each having a radius of 0.1 m, are placed symmetrically on either side of the wire. One loop is made of copper (conductivity = 5.8 × 10^7 S/m) and the other of a non-ferromagnetic material (conductivity = 3.0 × 10^7 S/m).
Capacitance in a Real-World Scenario?
A parallel plate capacitor is used in a fire alarm system. The plates are 5 cm apart and have an area of 0.05 m^2. The dielectric constant of the material between the plates is 3. The capacitance of the capacitor is 2 μF. How would you modify the capacitor to increase its capacitance by 50%?
A Box in Free Fall?
A box is dropped from a height of 100 meters above the ground. Considering air resistance to be negligible, calculate the time taken for the box to hit the ground. Additionally, consider the scenario where the box is dropped from a height of 50 meters. What implications does this have on the time taken for the box to hit the ground in both cases?
A Perfectly Inelastic Collision?
A 3 kg car collides with a 2 kg truck and they stick together after a perfectly inelastic collision. If the initial velocity of the car is 25 m/s and that of the truck is 10 m/s in the opposite direction, determine the velocity of the combined car-truck system after the collision.
Potential Differences in a Circuit?
Suppose you are designing a portable power bank with a capacity of 20,000 mAh. The power bank uses a rechargeable battery with an internal resistance of 0.5 Ω and an external resistance of 10 Ω in series. How would you determine the maximum potential difference across the power bank's terminals during charging, and what factors would you consider to minimize this potential difference?
Induction in a Coiled Wire?
A coiled wire is placed in a magnetic field. When the magnetic field is reduced by a factor of two in a time period of 1 second, and the radius of the coil is increased by 20%, what happens to the induced emf? Explain your reasoning with calculations to justify the effect on the emf.
A Car's Energy Efficiency?
A car travels from point A to point B using 120 kJ of energy. If it takes 20 minutes to cover this distance at a constant speed, what is the power consumption of the car during this journey? Assume the car's engine is 90% efficient.
Lifting a Magnet: What Happens?
Imagine you're holding a magnet suspended above a copper wire coil in a circuit. When you suddenly lift the magnet, the coil begins to generate a current. Explain why this happens and discuss the direction of the induced current in the coil.
Collision Impacts
A car traveling at 25 m/s collides with a stationary truck. If the mass of the car is 1500 kg and the truck's mass is 4000 kg, calculate the force exerted on the car during the collision, assuming an inelastic collision and neglecting air resistance. Consider the momentum conservation principle to justify your answer.
Effective Use of Pulleys?
In a factory, a 5 kg load is lifted using a pulley system consisting of a single movable pulley with a force of 50 N applied at an angle of 30° to the horizontal. How does the use of a pulley system in this scenario affect the efficiency of the work done in lifting the load compared to lifting it manually without a pulley?
Minimum Power Transfer Theorem?
In an AC circuit containing a resistor and an inductor, a variable capacitor is connected in parallel with the inductor. The capacitor's capacitance is slowly reduced from a very large value to a very small value. What happens to the power consumed by the inductor in the circuit as the capacitance reduces?
Gravitational Redshift Puzzle?
A laser is emitted from the surface of a celestial body, such as a white dwarf. If this laser signal reaches Earth, its frequency would be observed to be lower than its original frequency. How would the gravitational redshift of light from this celestial body relate to its mass and radius?
A Vehicle Pushed Up a Hill?
A car is being pushed up a 10° incline with a force of 200 N parallel to the slope. If the car's mass is 500 kg and it is moving at a constant speed, determine the force of friction opposing the motion.
Capacitor in Parallel: Equivalent Capacitance?
A circuit consists of two 4 μF and 6 μF capacitors connected in parallel. If a 12 V battery is connected across the circuit, calculate the equivalent capacitance and the charge stored in each capacitor.
Car Crashes: Friction to the Rescue?
In a car crash, friction between the tyres and the road helps in stopping the vehicle. However, if the vehicle is moving with a speed of 30 m/s, will it be possible to stop it within a distance of 20 m without any external assistance? Assume that the coefficient of kinetic friction between the tyres and the road is 0.5.
Motion in a Plane: Identifying the Centre of Mass?
Consider a uniform circular ring of mass 10 kg, with a radius of 0.5 m. A particle of mass 5 kg is placed on the ring at a distance of 0.2 m from its center. What would be the new location of the centre of mass of the system?
Motion of a Charged Particle in a Magnetic Field?
A charged particle with mass 9 × 10^-31 kg and charge 1.6 × 10^-19 C is moving at a speed of 5 × 10^6 m/s perpendicular to a magnetic field of strength 0.5 T. How will the particle's trajectory change if the magnetic field is doubled to 1 T? Explain your reasoning in terms of the force on the particle due to the magnetic field.
Motion in a Plane: A Projectile's Trajectory?
A particle is projected at an angle of 60° to the horizontal with an initial velocity of 20 m/s. If the particle lands 50 m away from the point of projection, what is the time it took to reach the ground, assuming a constant acceleration due to gravity of 9.8 m/s²?
Capacitor Connection Conundrum?
A 40 μF capacitor and a 20 μF capacitor are connected in series across a 400 V power supply. If the two capacitors are then disconnected from the power supply and connected in parallel, how much charge will be stored in each capacitor in the parallel configuration?
Conservation of Energy in a Circuit?
In an LCR series circuit with an AC voltage source, a resistor, an inductor and a capacitor are connected in series. When the circuit is connected to a power source, a current flows through the circuit. On the other hand, when the circuit is disconnected from the power source, the same components are left isolated and free to oscillate. How is energy conserved in this circuit during these two different scenarios?
Work Done by a Variable Force?
A 2000 N force is applied to a body, causing it to move from x = 0 to x = 2 m. If the force varies uniformly between 0 N and 2000 N, calculate the work done by the force on the body if it is displaced by 2 meters.
Have an academic question?
Stuck on a concept? Ask here — whether it's CBSE, ICSE, competitive exams, or any other subject you're learning. Our community and AI engine will answer with structured, exam-ready explanations.