Science Facts – SARKARI LIBRARY

Amplitude

Amplitude is the maximum displacement of a vibrating particle from its mean position.
In a wave, amplitude measures the height of the crest or depth of the trough from the rest position.
Greater amplitude means more energy carried by the wave.
Amplitude is always a positive quantity (distance measure).
It is measured in units of length (e.g., meters).
For a simple harmonic motion (SHM), amplitude is the maximum value of displacement (A).
In sound waves, amplitude relates to loudness — bigger amplitude means louder sound.
In transverse waves (like water waves), amplitude is vertical displacement.
In longitudinal waves (like sound in air), amplitude is density or pressure variation.
Amplitude does not affect frequency or period of a wave.
For a pendulum, amplitude is the maximum angular displacement from vertical.
In an equation $A\sin(\omega t)$ , A is the amplitude.
Energy in SHM ∝ $A^2$ (energy increases with square of amplitude).
Amplitude remains constant in ideal SHM without damping.
Damping causes amplitude to decrease gradually over time.
In light waves, amplitude relates to intensity/brightness.
In AC circuits, amplitude is the peak value of current or voltage.
Amplitude modulation (AM) varies the amplitude of a wave to carry information.
The peak-to-peak amplitude = 2 × amplitude.

Pitch

Pitch is the characteristic of sound that distinguishes shrill (high) sound from deep (low) sound.
Pitch of a sound depends on the frequency of vibration.
Higher frequency = Higher pitch.
Lower frequency = Lower pitch.
Pitch is measured in Hertz (Hz).
Sound waves with more vibrations per second have higher pitch.
Pitch is related to how the human ear perceives frequency.
Shrill sounds like a whistle have high pitch.
Bass sounds like thunder have low pitch.
Pitch is independent of loudness.
Loudness depends on amplitude, not pitch.
Pitch helps in distinguishing between male and female voices.
Female voices generally have higher pitch than male voices.
Children’s voices have higher pitch than adults.
Musical notes differ from each other mainly due to difference in pitch.
Pitch does not depend on the medium of sound propagation.
Two sounds with same loudness can have different pitch.
The unit of frequency, Hertz (Hz), represents cycles per second.
Ultrasonic sounds have very high frequency and pitch.
Infrasonic sounds have very low frequency and pitch.

SONAR

SONAR : Sound Navigation and Ranging.
uses sound waves to detect and locate objects underwater.
Principle: Works on the reflection of sound waves (echo).
Main Components:
- Transmitter: Produces sound waves.
- Receiver: Detects the reflected sound waves.
- Processor: Calculates distance, speed, and direction.
Speed of Sound in Water: Approximately 1,500 meters per second, faster than in air.

Echo

Echo is the reflection of sound that returns to the listener after striking a surface.
It is heard only if the reflected sound arrives after 0.1 seconds of the original sound.
For humans, this means the reflecting surface must be at least 17 meters away.
Echo helps in measuring distances using SONAR and RADAR techniques.
It is used by animals like bats and dolphins for echolocation.
Echo is louder if the reflecting surface is large and hard.
Soft materials absorb sound and do not produce echoes.
Echo is an example of sound reflection.
Echo is used in architectural acoustics to design auditoriums.
Echo can cause reverberation in enclosed spaces.
Echo is used in medical ultrasonography for imaging internal organs.

Reverberation

Reverberation is the persistence of sound in a space after the source stops.
It occurs due to multiple reflections of sound waves from walls, ceilings, and floors.
Reverberation adds richness to sound but can reduce speech clarity if excessive.
The time taken for sound to decay by 60 dB is called reverberation time.
Sabine formula is used to calculate reverberation time: $\frac{V}{A}$ , where V = volume, A = absorption.
Concert halls are designed for optimal reverberation to enhance music.
Auditoriums and classrooms aim for lower reverberation for better speech understanding.
Soft materials (curtains, carpets) absorb sound, reducing reverberation.
Hard surfaces (concrete, glass) reflect sound, increasing reverberation.
Excessive reverberation causes echo-like effects and distorted sound perception.

Wavelength

Wavelength is the distance between two consecutive crests or troughs of a wave.
It is denoted by the symbol λ (lambda).
The SI unit of wavelength is metre (m).
Wavelength is the distance traveled by a wave in one time period.
It is the length of one complete wave cycle.
Longer wavelength means lower frequency.
Shorter wavelength means higher frequency.
Wavelength is inversely proportional to frequency.
The relation between wave speed, frequency, and wavelength is: v = fλ.
In vacuum, the speed of light is 3 × 10⁸ m/s.
The wavelength of visible light ranges from 400 nm to 700 nm.
Red light has the longest wavelength in visible spectrum.
Violet light has the shortest wavelength in visible spectrum.
Wavelength depends on the medium through which the wave travels.
When light enters a denser medium, its wavelength decreases.
Frequency of light does not change with change of medium.
Sound waves have much longer wavelengths than light waves.
Wavelength is used to identify different types of electromagnetic waves.
Radio waves have the longest wavelength.
Gamma rays have the shortest wavelength.
Wavelength determines the energy of electromagnetic radiation.
Higher energy radiation has shorter wavelength.
Lower energy radiation has longer wavelength.

Frequency

Frequency( 𝑓) : Number of waves passing a point per second
- Unit : hertz (Hz)
- f = 1/ Time
Frequency is the number of oscillations or vibrations completed per second.
The SI unit of frequency is Hertz (Hz).
One hertz (1 Hz) means one cycle per second.
Frequency is denoted by the symbol f or ν (nu).
Frequency is the reciprocal of time period.
Formula: f = 1 / T, where T is time period.
Time period is the time taken to complete one oscillation.
The SI unit of time period is second (s).
Frequency does not depend on the amplitude of vibration.
Higher frequency means more oscillations per second.
In sound waves, frequency determines pitch.
Higher frequency sound has higher pitch.
Lower frequency sound has lower pitch.
The audible range of human hearing is 20 Hz to 20,000 Hz.
Sound waves with frequency below 20 Hz are called infrasonic waves.
Sound waves with frequency above 20,000 Hz are called ultrasonic waves.
Bats and dolphins use ultrasonic waves for navigation.
Frequency of light determines its color.
Frequency remains constant when a wave travels from one medium to another.
Speed of a wave = frequency × wavelength (v = fλ).
If frequency increases, wavelength decreases (for constant speed).
Frequency is measured using devices like frequency meters.
In AC current, frequency in India is 50 Hz.
In AC current, frequency in the USA is 60 Hz.
Radio waves have lower frequency than visible light.
Gamma rays have the highest frequency in the electromagnetic spectrum.
Frequency is a scalar quantity.
Unit of angular frequency is radian per second (rad/s).
Angular frequency (ω) is related to frequency by ω = 2πf.

Ultrasonic

Frequency Range : 20,000Hz
Heard by Humans : No
- Dogs & bats can hear ultrasonic sounds
Example : Bat echo, sonar, ultrasound
Human hearing range: 20 Hz to 20 kHz

Audible

Frequency Range : 20–20,000Hz
Heard by Humans : yes
Example : Human speech, music

Infrasonic

Frequency Range : <20Hz
Heard by Humans : No
Example : Earthquakes, elephant sounds

Time

The SI unit of time is second.
Atomic clocks are the most accurate clocks.
Cesium-133 atom is used in atomic clocks.
Earth takes 24 hours to rotate on its axis.
Earth takes about 365¼ days to revolve around the Sun.
Greenwich Mean Time (GMT) is based on the Prime Meridian.
Prime Meridian passes through Greenwich, London.
Indian Standard Time (IST) is 5 hours 30 minutes ahead of GMT.
- IST is based on 82.5° East longitude.
- Local time depends on longitude.
- Time difference of 1 hour corresponds to 15° longitude.
Earth rotates 1° in 4 minutes.
Sundial measures time using the Sun’s shadow.
Hourglass measures time using sand.
Water clock is also called Clepsydra.
Pendulum clock was invented by Christiaan Huygens.
Chronometer is used for precise time measurement (especially in ships).
Time zone is a region with the same standard time.
International Date Line is at 180° longitude.
Crossing the International Date Line eastward subtracts one day.
Crossing it westward adds one day.
Daylight Saving Time (DST) is used to save daylight in some countries.
India does not follow Daylight Saving Time.
UTC (Coordinated Universal Time) replaced GMT for scientific use.
Solar day is based on Earth’s rotation relative to the Sun.
Sidereal day is based on Earth’s rotation relative to stars.
Sidereal day is about 4 minutes shorter than a solar day.
Time dilation is a concept of Einstein’s Theory of Relativity.

Acceleration

Acceleration is the rate of change of velocity with respect to time.
SI unit of acceleration is m/s².
Acceleration is a vector quantity (has magnitude and direction).
Formula of acceleration: a = (v − u) / t.
If velocity increases, acceleration is positive.
If velocity decreases, acceleration is negative (called retardation).
Retardation is also known as deceleration.
Acceleration can occur due to change in speed, direction, or both.
Uniform acceleration means constant acceleration.
Non-uniform acceleration means changing acceleration.
Acceleration due to gravity on Earth is 9.8 m/s².
Acceleration due to gravity is denoted by g.
Free fall motion occurs under the influence of gravity only.
A body moving in a circular path has centripetal acceleration.
Centripetal acceleration is always directed towards the center.
Even at constant speed, circular motion has acceleration due to change in direction.
Zero acceleration means the body is either at rest or moving with constant velocity.
Instantaneous acceleration is acceleration at a particular instant of time.
Average acceleration = change in velocity / total time.
Acceleration-time graph gives change in velocity.
Area under acceleration-time graph represents change in velocity.
Slope of velocity-time graph gives acceleration.
Acceleration depends on the net force acting on the body.
According to Newton’s Second Law, F = ma.

Gravity

Gravity is a natural force that attracts objects toward each other.
Gravity pulls all objects toward the center of the Earth.
The gravity of the Earth is called gravitational force.
Gravity was discovered by Isaac Newton.
The law of gravity was proposed in 1687.
According to Newton, every object attracts every other object.
The force of gravity depends on mass and distance between objects.
Greater the mass, stronger is the gravitational force.
Gravity is weakest when objects are far apart.
The SI unit of gravitational force is Newton (N).
The gravitational constant is represented by G.
The value of G is 6.67 × 10⁻¹¹ Nm²/kg².
Acceleration due to gravity is denoted by g.
The value of g on Earth is approximately 9.8 m/s².
The value of g decreases with height and depth.
Gravity gives weight to objects.
Weight is the force with which Earth attracts a body.
Mass remains constant, but weight changes.
Gravity keeps the Moon in orbit around the Earth.
Gravity is responsible for tides in oceans.
Without gravity, objects would float freely.
Gravity plays an important role in the motion of planets.
The force of gravity on the Moon is one-sixth of that on Earth.
Gravity is a universal force.
Free fall occurs when an object moves under the influence of gravity only.

force

Force is a push or a pull acting on an object.
Force can change the shape, size, speed, and direction of an object.
Force can start or stop motion of a body.
The SI unit of force is Newton (N).
One Newton is the force required to accelerate a 1 kg mass by 1 m/s².
Force is a vector quantity (has magnitude and direction).
The formula of force is F = m × a.
Force depends on mass and acceleration.
The concept of force was explained by Isaac Newton.
Forces are classified as contact forces and non-contact forces.
Contact forces act only when bodies are in physical contact.
Examples of contact forces: friction, muscular force, normal force.
Non-contact forces act without physical contact.
Examples of non-contact forces: gravitational, magnetic, electrostatic.
Friction is a force that opposes motion between two surfaces in contact.
Gravitational force is always attractive in nature.
Magnetic force can be attractive or repulsive.
Force can produce rotation in an object.
Net force acting on an object determines its motion.
If net force is zero, the object remains at rest or in uniform motion.

velocity

Velocity is the rate of change of displacement with time.
It is a vector quantity (has magnitude and direction).
SI unit of velocity is metre per second (m/s).
Average velocity = Total displacement / Total time.
Instantaneous velocity is the velocity at a specific moment.
If velocity is constant, motion is uniform.
Zero velocity means the object is at rest.
Negative velocity indicates motion in the opposite direction of the reference.
Speed is scalar; velocity includes direction.
Uniform velocity → zero acceleration.
Change in velocity with time gives acceleration.
Displacement vs distance: displacement is used in velocity formula, distance is not.
For straight motion, velocity = +ve or –ve based on direction chosen.
Velocity vector can change even with constant speed (curved path).
Graph of displacement–time: slope = velocity.
Velocity–time graph: area under curve = displacement.
Relative velocity is velocity of one body relative to another.
In one-dim motion, if final and initial velocities are same → average velocity = that velocity.
With uniform acceleration: v = u + at (basic velocity formula).
Terminal velocity is max constant velocity in a resisting medium.

displacement

Displacement is the shortest distance between initial and final position.
It is a vector quantity (has both magnitude and direction).
SI unit of displacement is meter (m).
Displacement can be positive, negative, or zero.
If an object returns to its starting point, displacement is zero.
Displacement is independent of the path followed.
Displacement is always less than or equal to distance.
Distance can be non-zero while displacement is zero.
Displacement depends only on initial and final positions.
Average velocity is based on displacement, not distance.
Displacement can be represented by a straight line with direction.
In circular motion after one complete revolution, displacement is zero.
For motion in a straight line, displacement equals distance (if no change in direction).
Displacement can be measured along the straight line joining two points.
Zero displacement does not mean zero distance.
In projectile motion, displacement has horizontal and vertical components.
Displacement changes when the position changes, not with time directly.
Displacement can be calculated using vector addition.
Displacement is used to define velocity and acceleration.

mass

Mass is the amount of matter present in a body.
- Mass is a scalar quantity (has magnitude only, no direction).
- SI unit = kilogram (kg).
- CGS unit = gram (g).
Mass of a body remains constant everywhere.
Mass does not change with location (earth, moon, or space).
Mass is a measure of inertia of a body.
- Greater the mass, greater the inertia.
Mass is independent of gravity.
Mass can never be zero for a material object.
Mass is measured using a beam balance.
Mass is related to weight by the formula:
Weight = Mass × Acceleration due to gravity (W = mg).
Mass is a fundamental physical quantity.
Mass is not affected by temperature, pressure, or shape.
Mass helps determine momentum (Momentum = Mass × Velocity).
Mass is used in calculating force using Newton’s Second Law.
In space, mass remains same but weight becomes zero.
Mass of an object decides how difficult it is to change its motion.
Mass is additive (total mass = sum of individual masses).
Mass cannot be created or destroyed (Law of conservation of mass).