Search Previous Year Questions

The correct answer is Either plane or convex.

Key Points

• A plane mirror always forms an erect image, regardless of the distance of the object from the mirror.
• Convex mirrors also form erect images, but these images are diminished and located closer to the mirror.
• Both plane and convex mirrors are used in practical applications where erect images are required, such as in dressing mirrors (plane) and vehicle rear-view mirrors (convex).
• Concave mirrors can produce both erect and inverted images depending on the object's position relative to the focal point, making them unsuitable for this requirement.
• If the image is erect irrespective of the object's distance, the mirror is either plane or convex.

Additional Information

• Plane Mirror:
• Forms a virtual, erect, and same-sized image of the object.
• The image distance is equal to the object distance from the mirror.
• Used in household mirrors and optical instruments.
• Convex Mirror:
• Always forms virtual, erect, and diminished images.
• Used as rear-view mirrors in vehicles due to their wide field of view.
• Reflects light outward, making it ideal for surveillance and traffic mirrors.
• Concave Mirror:
• Forms real or virtual images depending on the object's position relative to the focal length.
• Used in telescopes, headlights, and shaving mirrors to focus light.
• Produces magnified erect images when the object is within the focal length.
• Image Characteristics:
• Virtual images cannot be projected onto a screen, while real images can.
• Erect images maintain the same orientation as the object.
• Inverted images flip the object's orientation vertically.

The correct answer is Right-hand thumb rule.

Key Points

• The Right-hand thumb rule is used to determine the direction of the magnetic field around a straight conductor carrying current.
• According to the rule, if you hold the conductor in your right hand with the thumb pointing in the direction of the current, the curl of your fingers represents the direction of the magnetic field lines.
• This rule is a simple and practical way to visualize the magnetic field created due to the flow of electric current.
• It is commonly applied in physics to understand the relationship between current flow and the generated magnetic field around a straight conductor.
• The magnetic field around the conductor forms concentric circles, which can be identified using this rule.

Additional Information

• Fleming's Left-Hand Rule:
• This rule is used to determine the direction of force experienced by a current-carrying conductor placed in a magnetic field.
• It relates the direction of current, magnetic field, and force using the thumb, forefinger, and middle finger of the left hand.
• Fleming's Right-Hand Rule:
• This rule is used to determine the direction of induced current when a conductor moves in a magnetic field.
• It relates motion, magnetic field, and induced current using the thumb, forefinger, and middle finger of the right hand.
• Magnetic Field:
• A region around a magnetic material or a current-carrying conductor where magnetic forces can be detected.
• Field lines are used to represent the magnetic field, and they form closed loops.
• Applications of Right-Hand Thumb Rule:
• Used in designing electrical instruments like solenoids and electromagnets.
• Helps in understanding the magnetic effects around current-carrying wires in practical applications.

The correct answer is Option 2 (18 m).

Key Points

• The displacement of the motorcycle is calculated using the formula for uniformly accelerated motion: s = (u + v)/2 × t, where 'u' is the initial velocity, 'v' is the final velocity, and 't' is the time.
• Given values: Initial velocity (u) = 5 m/s, Final velocity (v) = 7 m/s, Time (t) = 3 seconds.
• Substituting the values: s = (5 + 7)/2 × 3 = 12/2 × 3 = 18 m.
• The motorcycle travels a displacement of 18 meters in 3 seconds under uniform acceleration.
• This result is consistent with the kinematic equations of motion for uniformly accelerated systems.

Additional Information

• Uniformly Accelerated Motion:
• It refers to motion where the velocity of an object changes by an equal amount in every equal time interval.
• The kinematic equations of motion are applicable for this type of motion, which include formulas for displacement, velocity, and acceleration.
• Kinematic Equation for Displacement:
• The formula s = (u + v)/2 × t is used to calculate displacement when initial velocity, final velocity, and time are known.
• This equation is derived based on the assumption of uniform acceleration.
• Relation Between Velocity and Acceleration:
• Acceleration is the rate of change of velocity with respect to time and is constant in uniformly accelerated motion.
• It can be calculated using the formula: a = (v - u)/t.
• Displacement vs. Distance:
• Displacement is a vector quantity representing the shortest path between the initial and final points.
• Distance is a scalar quantity representing the total length of the path traveled, irrespective of direction.

The correct answer is 400 W.

Key Points

• The power required to lift a mass is calculated using the formula P = (m × g × h) / t, where m is mass, g is gravitational acceleration, h is height, and t is time.
• Given: m = 50 kg, g = 10 m/s², h = 8 m, and t = 10 s.
• Substituting values: P = (50 × 10 × 8) / 10 = 400 W.
• The minimum power required for lifting the mass is thus 400 Watts.
• Option 1 (400 W) is correct as per the calculation.

Additional Information

• Power: Power is the rate at which work is done or energy is transferred. The SI unit of power is the Watt (W).
• Work: Work is done when a force is applied to an object and it moves in the direction of the force. The formula for work is W = F × d, where F is force and d is displacement.
• Gravitational Force: The force exerted by the Earth on objects due to gravity. The acceleration due to gravity (g) is approximately 9.8 m/s², but for simplicity in calculations, it is often taken as 10 m/s².
• Energy: Energy is the capacity to perform work. Lifting an object vertically against gravity requires energy equal to the product of its weight and the height to which it is lifted.
• Efficiency: In practical applications, the power calculated is the theoretical minimum, assuming 100% efficiency. Real systems may require more power due to energy losses.

The correct answer is Newton's law of gravitation follows from Newton's laws of motion..

Key Points

• Newton's law of gravitation is a standalone law that describes the attractive force between two masses and is not derived from Newton's laws of motion.
• Newton's laws of motion describe the relationship between the forces acting on a body and its motion, but they do not explain why bodies exert gravitational attraction.
• Newton's law of gravitation was formulated based on observational data and is independent of the three laws of motion.
• The gravitational force between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them.
• Newton's laws of motion and the law of gravitation are foundational but distinct components of classical mechanics.

Additional Information

• Newton's Law of Gravitation:
• States that every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
• Mathematically: F = G (m₁m₂)/r², where G is the gravitational constant.
• Newton's Laws of Motion:
• First Law: A body remains at rest or in uniform motion unless acted upon by an external force (Law of Inertia).
• Second Law: The rate of change of momentum of a body is directly proportional to the applied force (F = ma).
• Third Law: For every action, there is an equal and opposite reaction.
• Gravitational Constant (G):
• A fundamental constant of nature with a value of approximately 6.674 × 10⁻¹¹ N(m²/kg²).
• It quantifies the strength of the gravitational force in Newton's law of gravitation.
• Gravitational Force vs. Weight:
• Gravitational force is the mutual force of attraction between two masses.
• Weight is the gravitational force exerted by the Earth on a body near its surface (Weight = mass × g).
• Gravitational Force at Earth's Center:
• At the center of the Earth, the gravitational force due to the Earth's mass cancels out, resulting in zero acceleration due to gravity (g = 0).

The correct answer is equal to its weight.

Key Points

• A body floats in a liquid when the buoyant force exerted by the liquid equals the weight of the body.
• The principle governing this phenomenon is Archimedes' Principle, which states that an object submerged in a fluid experiences an upward force equal to the weight of the fluid displaced.
• If the buoyant force is equal to the weight, the body achieves neutral buoyancy and floats.
• The body sinks if its weight is greater than the buoyant force.
• This balance between weight and buoyant force is essential for objects like ships and submarines to float efficiently on water.

Additional Information

• Buoyant Force:
• The upward force exerted by a fluid on an object placed in it, counteracting the weight of the object.
• This force is responsible for making objects float or feel lighter when submerged in liquids.
• Archimedes' Principle:
• Discovered by the ancient Greek mathematician Archimedes.
• It states: "The upward buoyant force exerted on a body immersed in a fluid is equal to the weight of the fluid displaced by the body."
• Density and Floating:
• An object floats if its density is less than the density of the liquid.
• If the densities are equal, the object remains submerged without sinking or floating (neutral buoyancy).
• Applications of Buoyancy:
• Shipbuilding: Ships are designed to displace water equal to their weight to float.
• Submarines: Adjust buoyancy using ballast tanks to sink or float.
• Hot air balloons: Use buoyancy in air to rise by heating air inside the balloon, reducing its density.

The correct answer is 2 N.

Key Points

• The buoyant force is calculated using Archimedes' principle: Buoyant force = ρ × V × g, where ρ is the density of the fluid, V is the volume of the object submerged, and g is the acceleration due to gravity.
• Given: Density of water (ρ) = 1000 kg/m³, Volume of sphere (V) = 2 × 10⁻⁴ m³, and g = 10 m/s².
• Using the formula: Buoyant force = (1000) × (2 × 10⁻⁴) × (10) = 2 N.
• The buoyant force is independent of the mass of the sphere; it only depends on the displaced fluid's volume and density.
• Therefore, the correct buoyant force exerted by water on the sphere is 2 N.

Additional Information

• Archimedes' Principle:
• It states that a body immersed in a fluid experiences an upward force equal to the weight of the fluid displaced by it.
• This principle is fundamental in calculating buoyant forces acting on submerged objects.
• Buoyant Force:
• The upward force exerted by a fluid on an object submerged in it.
• It depends on the fluid's density, the object's submerged volume, and gravitational acceleration.
• Density of Water:
• The standard density of water at room temperature is approximately 1000 kg/m³.
• It is one of the key parameters used in buoyancy calculations.
• Relation to Gravitational Force:
• Gravitational acceleration (g) impacts both the object's weight and the buoyant force exerted by the fluid.
• In standard conditions on Earth, g = 9.8 m/s² (rounded to 10 m/s² for simplicity in calculations).

The correct answer is 15 W.

Key Points

• The power dissipated by a resistive device can be calculated using the formula P = V²/R, where P is power, V is voltage, and R is resistance.
• The resistance of the bulb is derived from its rated values using R = V²/P. For a 60 W bulb at 220 V, R = (220)² / 60 = 806.67 Ω.
• When the potential difference is reduced to 110 V, the power dissipated is recalculated as P = (110)² / 806.67 ≈ 15 W.
• This reduction in power occurs because the power dissipation is proportional to the square of the voltage applied across the bulb.
• Thus, the power dissipated by the bulb at 110 V is approximately 15 W.

Additional Information

• Ohm's Law:
• Ohm's Law states that the current (I) through a conductor is directly proportional to the voltage (V) across it, and inversely proportional to its resistance (R): I = V/R.
• This principle helps in understanding the relationship between power, voltage, and resistance in electrical circuits.
• Power Formulae in Circuits:
• Power (P) can also be expressed as P = IV or P = I²R, depending on the known variables.
• These formulas are vital in analyzing energy consumption and dissipation in electrical devices.
• Resistive Load Behavior:
• For resistive loads like incandescent light bulbs, power dissipation is strongly dependent on the voltage applied across the load.
• Halving the voltage results in quartering the power dissipation, as power is proportional to the square of the voltage.
• Practical Implications:
• Operating a bulb at a lower voltage than its rated value reduces brightness and power output.
• Such reduced voltage operation can potentially extend the lifespan of the bulb but at the cost of reduced efficiency.
• Electrical Safety:
• Understanding power dissipation is essential for ensuring the safe operation of electrical devices and preventing overheating or fire hazards.

The correct answer is Converging lens.

Key Points

• A simple microscope uses a converging lens (also known as a convex lens) to magnify objects.
• The convex lens creates a magnified, virtual, and erect image of the object when placed at a distance shorter than the focal length of the lens.
• It is commonly used for low-magnification observations, such as reading fine print or examining small objects.
• The lens works based on the principle of refraction, bending light rays to converge and form an enlarged image visible to the human eye.
• Simple microscopes are easy to use and are often utilized in educational and general-purpose applications.

Additional Information

• Converging Lens (Convex Lens):
• A lens that is thicker at the center than at the edges, capable of focusing light rays to a single point (focal point).
• It is widely used in devices such as magnifying glasses, cameras, and telescopes.
• The focal length determines the degree of magnification achievable by the lens.
• Magnification:
• Magnification refers to how much larger or smaller the image of an object appears compared to the object itself.
• In a simple microscope, magnification is achieved by positioning the object within the focal length of the lens.
• Virtual Image:
• A virtual image is formed when light rays appear to diverge from a point, but do not actually meet.
• In a simple microscope, the image is virtual, meaning it cannot be projected onto a screen.
• Other Types of Lenses:
• Diverging lens (concave lens): Produces a virtual, diminished image and is not used in simple microscopes.
• Plane mirrors: Used to reflect light, but do not magnify images, hence unsuitable for microscopes.

The correct answer is Weight of the object.

Key Points

• The force with which the Earth attracts an object is called the weight of the object.
• Weight is determined by the gravitational force acting on the object's mass.
• The formula for weight is W = m × g, where 'm' is the mass of the object, and 'g' is the acceleration due to gravity (approximately 9.8 m/s² on Earth).
• Weight is a vector quantity, meaning it has both magnitude and direction; its direction is always toward the center of the Earth.
• Unlike mass, weight can change depending on the gravitational field strength (e.g., it is less on the Moon due to lower gravity).

Additional Information

• Mass: The quantity of matter in an object, measured in kilograms (kg). Mass is a scalar quantity and remains constant regardless of location.
• Density: Defined as mass per unit volume, represented by the formula ρ = m/V. It is a measure of how much mass is packed into a given volume.
• Gravitational force: A fundamental force of nature that attracts two bodies with mass toward each other. The gravitational force is responsible for the weight of objects on Earth.
• Magnitude: Refers to the size or quantity of a vector, such as force. It does not specify the nature or source of the force.
• On celestial bodies other than Earth, the gravitational acceleration 'g' differs, causing weight variations. For instance, on the Moon, gravity is approximately 1/6^th that of Earth.