11th Class Physics Chapter 7 Notes | Get Now
Chapter 7 is titled Oscillations and is part of the Punjab Board FSc Part 1 Physics syllabus. It builds on the concepts of motion and forces to explain how objects vibrate back and forth around a mean position.
Credit to taleem360.
Main topics covered in this chapter:
- Simple Harmonic Motion (SHM) and its characteristics
- Frequency and amplitude of oscillators
- Simple pendulum and its time period
- Phase angle and displacement equations
- Energy in SHM — kinetic, potential, and total
- Resonance and its real-life examples
- Damped oscillations and why motion stops
For More Notes Visit Now.
Short Questions & Answers from Chapter 7
The 11th Class Physics Chapter 7 Notes include 13 important short questions that are frequently asked in exams. Here is a quick summary of each:
Q 7.1 — Two Characteristics of SHM
Two key features of Simple Harmonic Motion are:
- The acceleration of a vibrating body is directly proportional to its displacement and always directed towards the mean position: a ∝ −x
- Total energy of the particle remains conserved: E_total = KE + PE = Constant
SHM can also be written mathematically as:
- x = x₀ sin(ωt + φ)
- x = x₀ cos(ωt + φ)
Q 7.2 — Does Frequency Depend on Amplitude?
No. The frequency of a harmonic oscillator is independent of amplitude.
- For a mass-spring system: f = (1/2π)√(k/m)
- For a simple pendulum: f = (1/2π)√(g/l)
In both cases, amplitude does not appear in the formula.
Q 7.3 — Can We Realize an Ideal Simple Pendulum?
No, we cannot. An ideal simple pendulum requires a heavy but tiny mass on a frictionless, inextensible string — conditions that are impossible to achieve in real life.
Q 7.4 — Total Distance in One Time Period
If the amplitude of SHM is A, the total distance travelled by the object in one complete time period is 4A.
Q 7.5 — Effect of Doubling Length or Mass of Pendulum
The time period of a simple pendulum is: T = 2π√(l/g)
- If length is doubled → T becomes √2 × T = 1.41 T
- If mass is doubled → No change in time period (mass is not in the formula)
Q 7.6 — Does Acceleration Remain Constant in SHM?
No. Acceleration varies with displacement because a = −ω²x. Since displacement keeps changing, acceleration changes too. At the mean position (x = 0), acceleration is zero.
Q 7.7 — What is Phase Angle?
Phase angle is the angle that specifies both the displacement and direction of motion of a point executing SHM. It does not define the angle between maximum displacement and driving force.
Q 7.8 — Conditions for Resultant SHM from Two SHMs
For two SHMs to produce a resultant SHM, the following conditions must be met:
- Both SHMs must be parallel (same direction)
- Both must be in phase
- Both must vibrate with the same frequency
Q 7.9 — Velocity and Acceleration in SHM
- At mean position (x = 0): velocity is maximum, acceleration is zero
- At extreme position (x = x₀): velocity is zero, acceleration is maximum
Q 7.10 — Explain the Equations of SHM
- y = A sin(ωt + φ): Gives instantaneous displacement, where A is amplitude, φ is initial phase, and ωt is angle subtended at time t
- a = −ω²x: Gives instantaneous acceleration, where ω is angular frequency and x is displacement
Q 7.11 — Energy Relationship in SHM
According to the law of conservation of energy:
- KE is maximum at mean position and zero at extreme position
- PE is maximum at extreme position and zero at mean position
- Total energy remains constant throughout the motion
Q 7.12 — Common Examples of Resonance
Resonance plays an important role in:
- Musical instruments
- Radio sets (electrical resonance at a specific frequency)
- Microwave ovens — waves of wavelength 12 cm at 2450 MHz cause food molecules to vibrate and heat up
Q 7.13 — Why Does a Mass-Spring System Eventually Stop?
When a mass-spring system is hung vertically and set into oscillation, it eventually stops because of air resistance and friction. These frictional forces dissipate energy as heat, so the system loses energy and stops oscillating.
Solved Problems — 11th Class Physics Chapter 7 Notes
The 11th Class Physics Chapter 7 Notes include 8 fully solved numerical problems. Here is a brief summary of each:
Problem 7.1 — Mass of Object on a Spring
Given: 100 g body elongates spring by 4 cm; unknown object has period of 0.568 s
Answer: Mass of object = 200 g
Problem 7.2 — Period, Spring Constant & Maximum Speed
Given: 15 g elongates spring by 2 cm; 294 g mass attached; amplitude = 10 cm
Answers:
- Time period = 1.256 s
- Spring constant = 7.35 N/m
- Maximum speed = 50 cm/s
Problem 7.3 — SHM with Restoring Force
Given: 8 kg body, amplitude 30 cm, restoring force 60 N at x = 30 cm; find values at x = 12 cm
Answers:
- Period = 1.3 s
- Acceleration = 3 m/s²
- Speed = 1.33 m/s
- Kinetic energy = 7.56 J
- Potential energy = 1.44 J
Problem 7.4 — Spring Compression by Falling Block
Given: 4 kg block dropped from 0.80 m onto spring (K = 1960 N/m)
Answer: Maximum compression = 18 cm
Problem 7.5 — Frequency of Simple Pendulum
Given: Pendulum length = 50 cm, g = 9.8 m/s²
Answer: Frequency = 0.70 Hz
Problem 7.6 — Velocity at Equilibrium Position
Given: Block of 1.6 kg, spring constant 1000 N/m, compressed 2 cm
Answer: Velocity = 0.50 m/s
Problem 7.7 — Car Vibration Frequency
Given: Car mass = 1300 kg, 4 springs each K = 20,000 N/m, passengers = 160 kg
Answer: Frequency of vibration = 1.18 Hz
Problem 7.8 — Amplitude, Frequency & Period from Equation
Given: x = 0.25 cos(π/8)t
Answers:
- Amplitude = 0.25 m
- Time period = 16 s
- Frequency = 1/16 Hz
- Displacement at t = 2 s → x = 0.18 m
Why These Notes Are Important for FSc Students
These 11th Class Physics Chapter 7 Notes are designed to help students:
- Revise all concepts quickly before exams
- Understand solved problems step-by-step
- Prepare short questions that are frequently repeated in Punjab Board papers
- Build a solid foundation for Chapter 8 (Waves) and beyond
You can also check our [internal link] FSc Part 1 Physics past papers and [internal link] important questions guide for extra exam preparation.
Key Formulas at a Glance
| Formula | Description |
|---|---|
| a = −ω²x | Acceleration in SHM |
| T = 2π√(m/K) | Period of mass-spring |
| T = 2π√(l/g) | Period of simple pendulum |
| f = 1/T | Frequency |
| v = ω√(x₀² − x²) | Velocity in SHM |
| KE = ½K(x₀² − x²) | Kinetic energy |
| PE = ½Kx² | Potential energy |
Suggested Image Alt Text: 11th Class Physics Chapter 7 Notes Oscillations Short Questions and Solved Problems
FAQs
Q1. What is Chapter 7 of 11th Class Physics about?
Chapter 7 of 11th Class Physics is about Oscillations. It covers Simple Harmonic Motion (SHM), simple pendulum, phase angle, energy conservation in SHM, resonance, and damped oscillations. It is an important chapter for FSc Part 1 board exams.
Q2. Where can I find 11th Class Physics Chapter 7 Notes online?
You can find complete 11th Class Physics Chapter 7 Notes on TaleemWorld.com. The notes include all 13 short questions with answers and 8 fully solved numerical problems as per the Punjab Board syllabus.
Q3. How many short questions are in Chapter 7 Physics FSc Part 1?
There are 13 short questions in Chapter 7 of FSc Part 1 Physics. These cover key topics like SHM characteristics, frequency, pendulum period, phase angle, resonance, and energy in oscillating systems.
Q4. What is Simple Harmonic Motion (SHM)?
Simple Harmonic Motion is a type of periodic motion where the acceleration of a body is directly proportional to its displacement from the mean position and is always directed toward the mean position. It is expressed as a ∝ −x.
Q5. Does the period of a simple pendulum change if mass is doubled?
No. The time period of a simple pendulum is T = 2π√(l/g), which does not include mass. So doubling the mass has no effect on the time period. Only the length of the pendulum and gravitational acceleration affect the period.
Q6. How many numerical problems are in FSc Part 1 Physics Chapter 7?
There are 8 solved numerical problems in Chapter 7. They cover topics like mass on a spring, spring constant, maximum speed, kinetic and potential energy, block compression, pendulum frequency, and displacement from an equation.