Physics – Study Notes for GTET (TET-2)
Overview
Physics forms a significant portion of the Mathematics and Science paper in GTET-2, covering fundamental concepts taught in classes 6-8. This section tests your understanding of everyday physical phenomena—how things move, why objects feel hot or cold, how light and sound behave, and how electricity powers our world.
For GTET-2, expect questions that blend conceptual understanding with practical applications. You must know definitions, units, simple numerical relationships, and real-life examples. The exam often presents scenario-based questions requiring you to apply physics principles to classroom situations or daily life contexts.
Mastering this topic requires clarity on basic laws and their observable effects rather than complex derivations. Focus on understanding "why" things happen alongside "what" happens—this dual approach helps tackle both direct and application-based questions.
Key Concepts
- Force is a push or pull that changes an object's state of rest or motion. It has both magnitude and direction (vector quantity). Contact forces require physical touch; non-contact forces (gravity, magnetism) act at a distance.
- Friction opposes relative motion between surfaces. Static friction prevents motion from starting; kinetic friction opposes ongoing motion. Friction depends on surface nature and normal force, not on contact area.
- Work is done only when force causes displacement in its direction. No displacement means no work, regardless of effort applied. Work transfers energy from one form to another.
- Energy exists in multiple forms—kinetic (motion), potential (position), heat, light, sound, electrical, chemical. Energy transforms but total energy remains constant (Law of Conservation of Energy).
- Heat flows from hotter to colder bodies until thermal equilibrium. Three modes: conduction (solids), convection (fluids), radiation (no medium needed).
- Light travels in straight lines (rectilinear propagation). Reflection follows two laws; refraction occurs due to speed change in different media. Mirrors form images by reflection; lenses by refraction.
- Sound needs a material medium to travel. Speed varies: fastest in solids, slowest in gases. Frequency determines pitch; amplitude determines loudness.
- Electric current is flow of charges through a conductor. A complete circuit is essential. Conductors allow current flow; insulators resist it. Magnets have poles; like poles repel, unlike poles attract.
Formulas / Key Facts
| Concept | Formula / Fact | Context |
|---|---|---|
| Speed | Speed = Distance ÷ Time | Basic motion calculation; unit is m/s or km/h |
| Work | Work = Force × Displacement × cos θ | Work done when force and displacement align; unit is Joule (J) |
| Kinetic Energy | KE = ½ × m × v² | Energy due to motion; m in kg, v in m/s |
| Potential Energy | PE = m × g × h | Energy due to height; g ≈ 10 m/s², h in metres |
| Power | Power = Work ÷ Time | Rate of doing work; unit is Watt (W) |
| Ohm's Law | V = I × R | Voltage = Current × Resistance; V in volts, I in amperes, R in ohms |
| Law of Reflection | Angle of incidence = Angle of reflection | Both measured from normal to the surface |
| Speed of Sound | ~340 m/s in air at room temperature | Increases with temperature; faster in solids than liquids |
| Speed of Light | 3 × 10⁸ m/s in vacuum | Light travels fastest in vacuum, slower in denser media |
Worked Examples
Example 1: Calculating Work Done
A boy pushes a box with a force of 50 N and moves it 4 metres along the floor. Calculate work done.
Solution:
- Force = 50 N, Displacement = 4 m (in direction of force)
- Work = Force × Displacement = 50 × 4 = 200 Joules
Example 2: Applying Ohm's Law
A torch bulb has resistance 20 ohms. If connected to a 3V battery, find the current flowing.
Solution:
- V = 3 V, R = 20 Ω
- Using V = I × R → I = V ÷ R = 3 ÷ 20 = 0.15 Amperes (or 150 mA)
Example 3: Image Formation in Plane Mirror
An object is placed 30 cm in front of a plane mirror. Where is the image formed and what are its characteristics?
Solution:
- Image distance = Object distance = 30 cm (behind the mirror)
- Characteristics: Virtual, erect, same size as object, laterally inverted
Common Mistakes
- Confusing mass and weight → Mass is amount of matter (kg), constant everywhere. Weight is gravitational force (N), changes with location. Weight = mass × g.
- Thinking friction is always harmful → Friction enables walking, writing, braking. Without friction, motion control would be impossible. It is harmful only when it causes wear or wastes energy.
- Believing work is done whenever force is applied → A person holding a heavy bag while standing does zero work on the bag (no displacement). Work requires movement in the direction of force.
- Assuming light always travels at the same speed → Light slows down in denser media (glass, water). This speed change causes refraction and bending of light rays.
- Mixing up series and parallel circuit properties → In series: same current, voltages add up, one break stops all. In parallel: same voltage, currents add up, one break doesn't affect others.
- Thinking sound travels in vacuum → Sound requires a medium. Astronauts cannot hear each other in space without radio equipment. Light travels through vacuum; sound cannot.
Quick Reference
- Force changes motion—no force means no change in velocity (Newton's First Law).
- Work = Force × Displacement—zero displacement means zero work regardless of force applied.
- Energy is conserved—it only transforms from one form to another, never created or destroyed.
- Heat flows hot to cold—conduction (contact), convection (fluid movement), radiation (waves).
- Light: reflection in mirrors, refraction in lenses—real images can be projected; virtual images cannot.
- Sound needs medium; light does not—sound travels fastest in solids, light travels fastest in vacuum.
- Ohm's Law: V = IR—doubling resistance at same voltage halves the current.
- Magnets: like poles repel, unlike attract—magnetic field lines flow from north to south pole externally.