Comprehensive solved notes on Unit 13 Relativity for Class 11 Physics students under the Federal Board of Intermediate and Secondary Education (FBISE), Islamabad. Similar to high-quality notes provided in institutions like APS, IMCB Islamabad, and other federal board colleges. Prepared by Hamdard Science Academy for the new NBF course (Cantab publisher). Covers special relativity, postulates, time dilation, length contraction, mass variation, mass-energy equivalence, and spacetime. Includes solved examples, derivations, MCQs, short questions, long questions, numericals, and assignments. For complete guide, solutions, easy notes, and help, download the full PDF at http://hsanotes.com. Join online classes :sharjeelmuhammad27@gmail.com
13.1 Definition of Relativity in Unit 13 Relativity FBISE Class 11 Physics
Relativity theory by Einstein describes relative space and time, challenging Newtonian absolute view. Encompasses special relativity (uniform motion) and general relativity (acceleration, gravity).
13.2 Explanation of Relativity in Unit 13 Relativity FBISE Class 11 Physics
Supersedes Newtonian mechanics for high speeds and strong gravity. Special relativity (1905): space-time relation in uniform motion. General relativity (1915): gravity as spacetime curvature. Impacts GPS, gravitational lensing, nuclear energy. Key: constant light speed implies relative space-time.
Frame of reference: coordinate system for measuring position, velocity, acceleration.
13.3 Inertial and Non-Inertial Frames in Unit 13 Relativity FBISE Class 11 Physics
Inertial: Newton’s first law holds; constant velocity or rest, no fictitious forces.
Non-inertial: accelerating; fictitious forces like centrifugal.
Example: Constant-speed bus (inertial); braking bus (non-inertial).
13.4 Special Theory of Relativity in Unit 13 Relativity FBISE Class 11 Physics
Postulates:
- Laws of physics same in all inertial frames.
- Speed of light c constant for all inertial observers.
Thought experiment: Mirror reflection in moving train illustrates time dilation.
13.5 Consequences of Special Relativity in Unit 13 Relativity FBISE Class 11 Physics
5.1 Relativity of Simultaneity: Events simultaneous in one frame may not be in another. Example: Lightning strikes on train.
5.2 Time Dilation: Moving clocks run slow. Δt = Δt₀ / √(1 – v²/c²). Derivation with light clock.
5.3 Length Contraction: Moving objects shorten in motion direction. L = L₀ √(1 – v²/c²). Derivation from time dilation.
5.4 Mass Variation: Relativistic mass m = m₀ / √(1 – v²/c²). Increases with speed.
Example: At 0.8c, m ≈ 1.67 m₀.
5.5 Mass-Energy Equivalence: E = mc². Mass convertible to energy.
Example: Nuclear reactions.
13.6 Spacetime as Four-Dimensional Model in Unit 13 Relativity FBISE Class 11 Physics
Space and time unified into spacetime. Events: (x, y, z, ct). Spacetime diagrams visualize worldlines. Minkowski space: flat spacetime in special relativity.
For detailed derivations and short questions on spacetime in unit 13 relativity, check PDF solutions.
Solved MCQs Unit 13 Relativity FBISE Class 11 Physics
- Theory of Relativity by: C. Albert Einstein
- Frame of reference is: D. arbitrarily fixed point for motion measurement.
- Pendulum period 5.0s rest, 10.0s observed: C. 0.866c
- Airliner at 200 m/s emits light: C. Travels at c, like all light.
- Inertial frame: D. All of these.
More solved MCQs in PDF.
Short Questions and Responses Unit 13 Relativity FBISE Class 11 Physics
13.1 Difference inertial/non-inertial: Inertial – Newton’s laws hold, constant velocity; non-inertial – accelerating, fictitious forces.
13.2 Postulates: 1. Physics laws same all inertial frames. 2. Light speed c constant.
13.3 Impossible faster than light: Mass infinite at c, requires infinite energy.
13.4 Reflection in light-speed train: Yes, light speed constant in train frame.
13.5 Density as speed increases: Increases as mass up, volume down (ρ = γ² ρ₀).
13.6 Relativity of simultaneity: Simultaneity frame-dependent due to constant c.
Full solved short questions in PDF.
Long Questions and Responses Unit 13 Relativity FBISE Class 11 Physics
13.1 Frames of reference: Coordinate system for motion. Types: Inertial (constant velocity, no fictitious forces); non-inertial (accelerating, fictitious forces). Example: Walking on train.
13.2 Postulates: 1. Physics laws invariant inertial frames. 2. c constant all observers.
13.3 Consequences: a) Simultaneity relative. b) Length contraction L = L₀ √(1-v²/c²). c) Time dilation Δt = Δt₀ / √(1-v²/c²). d) Mass m = m₀ / √(1-v²/c²). e) E=mc².
13.4 Time as fourth dimension: Unified spacetime (x,y,z,ct). Diagrams show worldlines. Minkowski space flat.
Full solved long questions in PDF.
Solved Numericals and Assignments Unit 13 Relativity FBISE Class 11 Physics
Assignment 13.1:
- Speed for half proper length: v ≈ 0.866c
- Pendulum period 3s rest, observer speed 0.95c: Δt ≈ 9.608s
Numerical 13.1: Electron energy: 0.511 MeV
13.2: Spaceship 100m at 0.99c: L ≈ 14m
13.3: π-mesons at 2.70×10⁸ m/s, rest 2.60×10⁻⁸ s: Lab lifetime ≈ 5.96×10⁻⁸ s
13.4: π-meson lab 1.40×10⁻¹⁶ s, rest 0.840×10⁻¹⁶ s: v = 0.8c
Full solved numericals and assignments in PDF for easy notes and solutions.
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