Physics Past Paper Common Questions by Vasumitra Gajbhiye

1. Motion, Forces, and Energy

• Work Done and Energy Changes

  • As a trolley moves across a rough surface:
    • Work is done against friction.
    • Kinetic energy decreases to zero, converted to thermal energy.

• Toppling of a Bus

  • Occurs when the line of center of mass falls outside its base.

• Conservation Principles

  • Momentum: In an isolated system, total momentum remains constant.
  • Energy: In a closed system, total energy is conserved.

• Center of Mass: Point where mass is concentrated.

• Equilibrium Conditions:

  • No resultant force.
  • Sum of clockwise moments equals anticlockwise moments.

Hooke's Law

• Extension is proportional to load until the elastic limit.
• Stored Energy: Strain/elastic potential energy.

Terminal Velocity

• Motion in Fluid:
  • Initial acceleration by gravity, drag increases with speed.
  • Terminal velocity is reached when weight equals resistance.

Particles Arrangement and Motion

• Gases: Molecules move randomly at high speeds, collide with each other.
• Solids: Molecules arranged in a lattice, vibrate in place.
• Liquids vs. Solids: Liquids have molecules that can move and are slightly further apart.
• Gases vs. Liquids: Gas molecules are further apart with weaker intermolecular forces.

Gas Pressure

• Exerted when molecules collide with container walls, changing momentum.
• Volume and Pressure Relationship: Pressure decreases as volume increases due to fewer collisions.

Moment

• The turning effect of a force about a pivot.

2. Thermal Physics

Conduction

• In Metals: Energy transferred through vibrating atoms and mobile electrons.
• In Non-metals: Through molecular vibrations and collisions.

Liquids & Gases

• Boiling: Energy used to break intermolecular bonds, allowing molecules to escape as vapor.
• Compression: Liquids are incompressible due to close molecular arrangement.

Evaporation

• Heat energy causes some surface molecules to gain enough kinetic energy to escape.
• Cooling effect as more energetic molecules leave.

Thermometer

• Range and Sensitivity:
  • Increase range with longer capillary or smaller bulb.
  • Sensitivity increased with a thinner capillary or larger bulb.

3. Waves

Sound

• Longitudinal Waves: Compressions and rarefactions travel parallel to wave direction.
• Transverse Waves: Vibrate perpendicularly to wave direction.

Light

• Total Internal Reflection: Occurs when light in a denser medium hits boundary at an angle greater than critical angle.
• Fiber Optics: Use of light reflection within fibers for medical and communication purposes.

4. Electricity and Magnetism

DC Motors

• Split-Ring Commutator: Reverses current direction every half turn, ensuring continuous rotation.

Transformers

• Operate on AC to induce voltage via changing magnetic fields.
• Higher transmission voltages reduce power losses.

Safety

• Earthing: Prevents electrocution by keeping metal cases at ground potential.
• Fuses and Circuit Breakers: Protect circuits from overcurrent and prevent hazards.

5. Nuclear Physics

Nuclear Reactions

• Fusion: Joining small nuclei to form heavier ones releasing energy.
• Fission: Splitting heavy nuclei into lighter ones.

Radiation Safety

• Use shielding and secure storage and handling to minimize exposure risks.

6. Space Physics

Universe and Big Bang Theory

• Redshift: Evidence of universe expansion; galaxies moving away.
• Big Bang: Universe started from a tiny point and expanded.

Stellar Evolution

• Stages of Stars: From protostar, main sequence, red giant, to white dwarf or supernova.
• Nuclear Fusion: Occurs at high temperatures overcoming electrostatic repulsions.

Gravitational Forces

• Gravity causes planetary and moon orbits, maintains elliptical paths.

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These notes cover key concepts from the physics past paper, providing concise explanations of motion, energy, waves, thermal physics, electricity, nuclear physics, and space physics, aiding in efficient study and understanding of fundamental principles.