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Board exam questions from CBSE, ICSE, and all State Boards — answered with AI-structured explanations and community insights.
Can a charged object be made to attract another object of the same charge?
A small plastic rod is rubbed with a cloth, resulting in the transfer of electrons. The rod then attracts a small piece of paper, but not a second identical plastic rod. Analyze the phenomenon and explain the underlying principle.
Electrostatic Shielding of a Charged Object?
A small charged object of 10 cm radius is placed inside a hollow metal sphere of 20 cm radius. What happens to the electric field and potential outside the sphere when the object is brought near the center of the sphere, and how does it affect the capacitance of the sphere?
Motion of a Charged Particle?
A charged particle moves along a uniform electric field. If the electric field is increased by a factor of 4, how will the path of the particle change? Explain with a neat diagram and support your answer with relevant concepts from the chapter.
Roller Coaster Safety in Rotation?
Imagine a roller coaster car with four passengers, each with a mass of 60 kg. If the car is rotating at a constant speed of 5 m/s in a circular path of radius 10 m, and the car's angular velocity suddenly decreases to half its original value while the linear velocity remains the same, what happens to the force of friction acting on each passenger, and why?
Power of a Variable Force?
A particle is moving along a straight line under the influence of a variable force F(t) = 2t N, where time t is in seconds. Calculate the work done by this force in moving the particle from x = 1 m to x = 3 m. Explain your reasoning.
How does the Electric Field affect the trajectory of charged particles?
A charged particle of mass 1 kg and charge 2 μC is projected into a uniform electric field of 4 × 10^4 N/C. If the particle is projected at an angle of 60° with the direction of the electric field, what will be its trajectory and how will it change if the charge is doubled?
How does the presence of a moving conductor affect the magnetic field strength?
A straight copper wire of length 2 m is moving with a constant velocity of 10 m/s in a direction perpendicular to a magnetic field of 0.5 T. What happens to the magnetic field strength when the wire is moving in the same direction as the magnetic field? In a different direction? Assume the wire's cross-sectional area is negligible.
Magnetic Field Lines and Matter Interaction?
A rare-earth magnet is placed near a paper clip. Describe the changes in the magnetic field lines and their interactions with the paper clip, assuming the magnet's strength remains constant.
Capacitor in Parallel: How does it affect the Total Capacitance?
Three capacitors of 10 μF, 20 μF, and 30 μF are connected in parallel across a 200 V supply. What is the total capacitance of the combination and how does it compare with the capacitance of each individual capacitor?
Car Crash Scenario?
A car is traveling at a constant speed of 20 m/s when the driver suddenly applies the brakes to avoid hitting a child standing on the road. Meanwhile, a tree is approaching the car at a speed of 5 m/s. What is the minimum coefficient of friction required between the car's tires and the road to prevent the car from hitting the tree?
Why does a long straight wire carry current produce a magnetic field?
A current-carrying long straight wire is placed parallel to a cylindrical conductor made of a non-ferromagnetic material. The wire carries a current of 5 A, and the cylinder has a radius of 0.5 m. Explain how the direction of the magnetic field produced by the wire can be determined using the right-hand rule in different situations – when the wire and cylinder are stationary, and when the wire is moving past the cylinder while the cylinder is stationary.
Torque and Angular Momentum?
A rigid bar of length 1.5 m and mass 4 kg is suspended from a fixed point by two ropes, each of length 0.5 m. What is the angular momentum of the bar about the point of suspension, assuming the ropes are massless and the motion is confined to a vertical plane?
Gravitational Binding Energy?
Consider two objects with masses m and M separated by a distance r. How does the gravitational binding energy of the system change if the distance between the objects is doubled while keeping their masses constant?
Lifting a Lift Off?
A DC motor is used to power a lift in an amusement park, and suddenly the power supply is interrupted due to a short circuit. Explain the effect on the current flowing through the motor and the lift's motion.
Inertia and Force
A 50 kg box is placed on a frictionless surface. What force would you apply to the box to move it at a constant acceleration of 2 m/s^2, assuming you have an infinite supply of time and energy? Ignore any safety concerns or practical limitations.
Induced Voltage in Alternating Fields?
A conductor is placed in an alternating magnetic field of frequency 50 Hz. Explain, with suitable mathematical reasoning, how the induced voltage in the conductor changes with time, assuming the magnetic field's amplitude remains constant.
Magnetic Field and Lenz's Law Inversion?
A superconducting material, when cooled, exhibits perfect diamagnetism. You are given a long solenoid with its axis aligned with the radius of a superconducting ring. When the current in the solenoid is switched on, devise a method to induce a current in the superconducting ring using the principle of electromagnetic induction.
Kirchhoff's Loop Rule Conundrum?
In a circuit containing a 2 Ω resistor, a 3 V battery, and an unknown inductor, the total resistance is measured to be 5 Ω. Using only Kirchhoff's loop rule, derive an expression for the inductance of the inductor and discuss its implications on the circuit.
Universal Gravitation - A Scale Model?
Imagine you are designing a scale model of the solar system, where the Sun is represented by a basketball, and the planets are represented by smaller balls. If the Earth's mass is 6 x 10^24 kg, and its radius is about 6.37 x 10^6 m, what should be the radius of a scale model, where the Sun is 1 m in diameter, to ensure that the gravitational force between the Earth and the Sun is the same in both the real and the model system?
Uniform Circular Motion?
A 5 kg particle is moving in a circular path of radius 20 m on a frictionless surface. If the particle completes one full revolution in 2 s, calculate the work done on the particle by an external force acting tangentially, assuming it has an initial speed of 2 m/s. Can you justify your answer?
Induced EMF in a Rotating Coil?
A coil of radius 20 cm, with 100 turns, rotates about its diameter in a uniform magnetic field of 0.2 T. If the coil makes 50 revolutions in 20 seconds, what is the average induced EMF in the coil?
Magnetic Field of a Solenoid?
A current of 2 A flows through a solenoid of 100 turns and length 0.1 m. If the magnetic field inside the solenoid is 100 μT, what is the magnetic moment of the solenoid? Assume the current is switched off and then the solenoid is used as a magnet. How would the magnetic moment change if the number of turns is doubled and the length is halved?
Motion of Charged Particles in Electric Fields?
A uniform electric field of 2 × 10^4 N/C is directed along the positive x-axis. A particle with charge 6 × 10^-8 C is moving in this field with an initial velocity of 2 × 10^5 m/s. If the particle is released from rest at a distance of 1 m from the point where the electric field is measured, what will be its speed when it reaches the point of release?
Effect of Temperature on Resistivity?
The resistivity of a conductor increases with an increase in temperature. However, a certain metal shows a decrease in resistivity with an increase in temperature. What could be the reason for this anomaly and how would you verify it experimentally?
Motion in a Plane: Dilemma of the Projectile?
A projectile is launched with an initial velocity of 100 m/s at an angle of 60° above the horizontal. Assuming negligible air resistance, how would you modify the launch velocity to ensure that the projectile lands at the same point from which it was launched?
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