Physics — TN TET Paper II Study Notes

Overview

Physics forms a significant component of the Mathematics and Science section in TN TET Paper II, which assesses candidates for teaching classes 6–8. Questions test both your conceptual understanding of physical phenomena and your ability to explain these concepts to young learners. The syllabus covers four major domains: force, motion and work; heat and light; electricity and magnetism; and sound.

Expect around 8–12 questions from physics, blending direct conceptual questions with application-based problems. The key is to understand principles at the level you would teach them—clear definitions, simple numerical relationships, and everyday examples. Examiners favour questions that check whether you can distinguish between related concepts (force vs pressure, heat vs temperature) and apply formulas to straightforward problems.

Mastering this section requires memorising key formulas, understanding the physical meaning behind each, and practising typical numerical problems involving speed, work, power, resistance, and reflection/refraction.

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Key Concepts

• **Force** is a push or pull that changes the state of rest or motion of an object. Measured in newtons (N). Contact forces include friction; non-contact forces include gravity and magnetism.

• **Friction** opposes relative motion between surfaces. Types: static (prevents motion), sliding (during motion), rolling (least resistance). Friction depends on surface nature and normal force, not on area of contact.

• **Newton's Laws**: (1) Inertia—objects remain at rest or uniform motion unless acted upon by a force. (2) F = ma—acceleration is proportional to net force. (3) Action-reaction—forces always occur in pairs.

• **Work** is done only when force causes displacement in the direction of force. W = F × d × cos θ. No displacement or perpendicular force means zero work.

• **Energy** is the capacity to do work. Forms: kinetic, potential, heat, light, sound, chemical, electrical. Law of conservation—energy transforms but total remains constant.

• **Heat vs Temperature**: Heat is total thermal energy transferred (joules); temperature is a measure of average kinetic energy of particles (°C, K). Heat flows from higher to lower temperature.

• **Modes of heat transfer**: Conduction (solids, particle vibration), convection (liquids/gases, bulk movement), radiation (no medium needed, electromagnetic waves).

• **Light travels in straight lines** (rectilinear propagation). Speed in vacuum = 3 × 10⁸ m/s. Reflection follows laws: angle of incidence = angle of reflection; incident ray, reflected ray, and normal lie in the same plane.

• **Refraction** is the bending of light when it passes from one medium to another due to change in speed. Denser medium → light bends towards normal.

• **Electric current** is the flow of electric charge. Conventional current flows positive to negative; electron flow is opposite. Measured in amperes (A).

• **Ohm's Law**: V = IR. Voltage (V) = Current (I) × Resistance (R). Valid for ohmic conductors at constant temperature.

• **Sound** is a mechanical wave requiring a medium. It travels fastest in solids, slowest in gases. Frequency determines pitch; amplitude determines loudness.

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Formulas / Key Facts

| Concept | Formula / Fact | |---------|----------------| | Speed | Speed = Distance ÷ Time (m/s) | | Velocity | Velocity = Displacement ÷ Time (vector quantity) | | Acceleration | a = (v − u) ÷ t | | Force | F = m × a (newton = kg·m/s²) | | Weight | W = m × g (g ≈ 9.8 m/s² or 10 m/s² for approximation) | | Pressure | P = F ÷ A (pascal = N/m²) | | Work | W = F × d (joule = N·m) | | Power | P = W ÷ t (watt = J/s) | | Kinetic Energy | KE = ½ mv² | | Potential Energy | PE = mgh | | Ohm's Law | V = I × R | | Resistance in series | R_total = R₁ + R₂ + R₃ | | Resistance in parallel | 1/R_total = 1/R₁ + 1/R₂ + 1/R₃ | | Electric Power | P = V × I = I²R = V²/R | | Mirror/Lens formula | 1/f = 1/v + 1/u | | Speed of sound in air | ≈ 340 m/s at 20°C | | Speed of light in vacuum | 3 × 10⁸ m/s |

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Worked Examples

**Example 1 — Work and Power**

A boy pushes a box with a force of 50 N through a distance of 10 m in 5 seconds. Find work done and power.

• Work = F × d = 50 × 10 = 500 J
• Power = W ÷ t = 500 ÷ 5 = 100 W

**Example 2 — Ohm's Law**

A resistor of 20 Ω is connected to a 12 V battery. Find the current flowing through it.

• V = IR → I = V ÷ R = 12 ÷ 20 = 0.6 A

**Example 3 — Kinetic Energy**

A car of mass 1000 kg is moving at 20 m/s. Calculate its kinetic energy.

• KE = ½ mv² = ½ × 1000 × 20² = ½ × 1000 × 400 = 200000 J = 200 kJ

**Example 4 — Reflection**

A light ray strikes a plane mirror at 35° to the mirror surface. Find the angle of reflection.

• Angle of incidence is measured from normal, not surface.
• Angle with normal = 90° − 35° = 55°
• Angle of reflection = 55° (law of reflection)

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Common Mistakes

• **Confusing mass and weight** → Mass is constant everywhere (kg); weight varies with gravity (N). Weight = mass × g.

• **Calculating work when force is perpendicular to motion** → Work is zero when force and displacement are at 90°. A porter carrying load on head while walking horizontally does zero work against gravity.

• **Mixing up heat and temperature** → A cup of boiling water and a bucket of warm water may have the same temperature, but the bucket has more heat (more mass).

• **Using wrong angle in reflection** → Always measure angle from the normal, not from the mirror surface.

• **Forgetting unit conversions** → Ensure consistent units. Convert km/h to m/s by multiplying by 5/18. Convert minutes to seconds before using formulas.

• **Series vs parallel confusion** → In series, current is same but voltage divides. In parallel, voltage is same but current divides.

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Quick Reference

• Force = mass × acceleration; unit is newton (N)
• Work = force × displacement; unit is joule (J)
• Power = work ÷ time; unit is watt (W)
• V = IR (Ohm's Law) — memorise rearrangements: I = V/R, R = V/I
• Angle of incidence = Angle of reflection (measured from normal)
• Sound needs a medium; light does not
• Heat transfers by conduction, convection, radiation — radiation is the only method that works in vacuum