SSLC: Physics Notes
Physics Study Notes (Part 1)
1. Sound Waves
• Oscillation: A periodic motion in which an object moves to and fro at regular intervals of time about its equilibrium position.
◦ One oscillation is completed when the body returns to its initial position in the same direction from where it started.
◦ Example: A swing completes one oscillation when the pendulum starts from O, goes to both sides, and then returns to O. Or, if starting from A, it reaches B and returns to A.
• Amplitude (a): The magnitude of maximum displacement to one side from its equilibrium position.
◦ SI Unit: metre (m).
• Period (T): The time taken for one oscillation.
◦ SI Unit: second (s).
◦ Formula: T = Total time / Number of oscillations.
• Frequency (f): The number of oscillations in one second.
◦ SI Unit: hertz (Hz).
◦ Formula: f = Number of oscillations / Time.
◦ Relation to Period: f = 1/T. As the period increases, frequency decreases.
◦ Practical Units: Kilohertz (kHz) = 1000 Hz = 10³ Hz; Megahertz (MHz) = 1,000,000 Hz = 10⁶ Hz.
• Heinrich Rudolf Hertz (1857-1894): Experimentally proved the presence of electromagnetic waves and discovered the photoelectric effect, laying the foundation for radio, telephone, telegraph, and television. The unit of frequency, hertz, is named in his honour.
• Natural Frequency: The innate frequency at which an object vibrates freely.
◦ Factors influencing natural frequency: Length of the object, Size of the object, Elasticity, Nature of the material.
• Forced Vibration: The vibration of an object induced by an external vibrating object.
◦ Example: A table vibrating due to a mixie, or a table vibrating when a tuning fork stem is pressed on it, making the sound louder.
• Resonance: Occurs if the natural frequency of the forcing object and that of the forced object are equal.
◦ Objects undergoing resonance will vibrate with maximum amplitude.
◦ Example: Hacksaw blades C and E vibrating with maximum amplitude when blade A vibrates, because their natural frequencies are equal to A's. A louder sound heard when varying the air column length in a pipe with a 512 Hz tuning fork.
◦ Applications: MRI scanning, Radio tuning, Musical instruments (guitar, violin, veena, harmonium, mridangam, trumpets, nagaswaram), Stethoscopes.
• Wave Motion: A mode of transfer of energy from one part of the medium to other parts.
◦ It is the continuous propagation of energy from one part to the other parts through oscillations.
◦ The disturbance spreads without the displacement of the medium's particles (e.g., slinky coils).
• Types of Waves:
◦ Mechanical Waves: Require a medium for transmission.
▪ Longitudinal Waves: Particles in the medium vibrate parallel to the direction of propagation of the wave.
• Features: Compressions (regions of high pressure, decreased molecular distance) and rarefactions (regions of low pressure) are formed. Pressure variations occur.
• Example: Sound waves (sound travels through air forming alternating compressions and rarefactions).
▪ Transverse Waves: Particles of a medium vibrate perpendicular to the direction of propagation of the wave.
• Features: Crests (elevated portions from equilibrium position) and troughs (lowest portions from equilibrium position) are formed. No pressure variations occur.
• Example: Waves on a string.
◦ Electromagnetic Waves: Do not require a medium for transmission. They are transverse waves.
▪ Examples: Radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X-rays, gamma rays.
• Characteristics of Waves:
◦ Amplitude: The maximum displacement from the equilibrium position of the wave.
◦ Frequency: The number of cycles that pass through a point in one second.
◦ Period: The time taken by the particle in the medium to complete one vibration.
◦ Wavelength (λ): The distance between two consecutive particles which are in the same phase of vibration.
▪ Also, the distance travelled by the wave during the time taken by each particle in the medium to complete one vibration.
▪ For transverse waves: Distance between two consecutive crests or troughs.
▪ For longitudinal waves: Distance between two consecutive compressions or rarefactions.
▪ Unit: metre (m).
◦ Speed of Wave (v): The distance travelled by the wave in one second.
▪ Unit: m/s.
▪ Relation: v = fλ (Speed of a wave = frequency × wavelength).
▪ When speed is constant, frequency is inversely proportional to wavelength (f ∝ 1/λ).
• Reflection of Sound: Sound waves reflect when they hit objects.
◦ Smooth surfaces reflect sound more effectively than rough surfaces.
◦ Applications: Soundboards, Curved ceilings in halls (help spread sound).
◦ Multiple Reflection of Sound: Reflected sound waves get reflected again.
• Echo: The sound heard after a while due to the reflection of the initial sound.
◦ Persistence of Hearing: The auditory experience produced by a sound persists for about 1/10 of a second. If another sound falls on the ear during this time, it is felt as if they are heard together.
◦ Minimum distance for distinct echo: Sound must travel at least 35 m (for 350 m/s speed of sound) to allow for 0.1 s persistence of hearing. Therefore, the reflecting surface must be at least 17.5 m away.
◦ Example Calculation: If echo of a firecracker is heard after 1 s (speed 350 m/s), total distance travelled = 350 m/s × 1 s = 350 m. Distance to reflecting surface (d) = Total distance / 2 = 350 m / 2 = 175 m.
• Reverberation: The lingering of sound, even after the original sound has ceased.
◦ It is due to the multiple reflection of sound and the boom fades away gradually.
◦ Example: Whispering gallery of Gol Gumbaz.
◦ To prevent excessive reverberation in large halls (like cinema theatres), walls are made rough to decrease loudness of reflecting sound.
• Limits of Audibility:
◦ For a person with normal hearing: 20 Hz (lower limit) to 20000 Hz (20 kHz, upper limit).
◦ Infrasonic: Sound with a frequency below 20 Hz.
▪ Audible to: Elephants, pigeons.
◦ Ultrasonic: Sound with a frequency more than 20000 Hz.
▪ Audible to: Bats, dogs, moths.
▪ Uses: Medical diagnosis and treatment (crushing kidney stones, physiotherapy, imaging internal organs - ultrasonography), Cleaning spiral tubes and machine parts, used in SONAR (to find distance to underwater objects).
• Seismic Waves: Waves that travel through the Earth's crust due to earthquakes, volcanic eruptions, and massive explosions.
◦ Seismology is the study of seismic waves. Intensity is determined by the Richter scale.
• Tsunami: A series of gigantic ocean waves caused by the displacement of large volumes of water in the sea, often triggered by undersea earthquakes.
2. Lenses
• Lens: A transparent medium in which each refracting surface is part of spheres.
• Convex Lens:
◦ Thicker in the middle.
◦ Converges light rays.
◦ Shows objects magnified.
◦ When observed through, letters appear to move in the opposite direction when the lens is moved.
◦ Principal Focus (F): Light rays near and parallel to the optic axis incident on a convex lens, after refraction, converge at a point on the optic axis on the other side of the lens. This focus is considered real because light rays actually pass through it.
• Concave Lens:
◦ Thinner in the middle.
◦ Thicker at the edges.
◦ Diverges light rays.
◦ When observed through, letters appear to move in the same direction when the lens is moved.
◦ Principal Focus (F): Light rays near and parallel to the optic axis incident on a concave lens, after refraction, appear to diverge from a point on the optic axis on the same side of the lens. This focus is considered virtual because refracted rays do not actually pass through it.
• Terms Related to Lenses:
◦ Optic Centre (O): The midpoint of a lens.
◦ Centres of Curvature (C1, C2): The centres of the spheres of which each refracting surface of a lens is a part.
◦ Optic Axis: The imaginary line passing through the centres of curvature and the optic centre of a lens.
◦ Aperture: The area of the lens through which light passes. It can be varied in optical instruments.
◦ Focal Length (f): The distance from the optic centre of the lens to the principal focus.
• Image Formation by Lenses:
◦ Real Images: Images that can be projected on a screen. Examples: Images captured on a camera, images formed on a cinema screen.
◦ Virtual Images: Images that cannot be captured on a screen, but can only be seen.
• Convex Lens Image Characteristics (based on object position):
◦ Beyond 2F: Image between F and 2F on the other side; Diminished, Inverted, Real.
◦ At 2F: Image at 2F on the other side; Same size, Inverted, Real.
◦ Between F and 2F: Image beyond 2F on the other side; Magnified, Inverted, Real.
◦ At F: Image at infinity; Highly magnified, Inverted, Real (rays converge at infinity).
◦ Between F and Lens (O): Image on the same side of the object; Magnified, Erect, Virtual.
• Concave Lens Image Characteristics:
◦ Always forms a virtual, diminished, and erect image.
◦ The image position is always between F and the lens on the same side of the object. This is because a concave lens diverges light rays.
• Lens Equation: Relates focal length (f), object distance (u), and image distance (v).
◦ Formula: 1/f = 1/v - 1/u.
◦ Can also be written as: f = (uv) / (u - v).
• Cartesian Sign Convention (for lenses):
◦ All distances should be measured from the optic centre of the lens.
◦ Distances measured in the same direction as the incident ray are positive.
◦ Distances measured in the opposite direction of the incident ray are negative.
◦ Distances measured above the optic axis are positive.
◦ Distances measured below the optic axis are negative.
• Magnification (m): How many times the height of the object is to the height of the image.
◦ It is the ratio of the height of the image (hi) to the height of the object (ho). It has no unit.
◦ Formula: m = hi / ho.
◦ Also: m = v / u (Distance to the image / Distance to the object).
◦ Sign interpretation:
▪ Positive magnification: Image is erect.
▪ Negative magnification: Image is inverted.
▪ |m| < 1: Image is diminished (smaller than object).
▪ |m| = 1: Image is same size as object.
▪ |m| > 1: Image is magnified (larger than object).
• Power of Lens (P): The ability of a lens to converge or diverge light rays incident on it.
◦ Power is the reciprocal of focal length. The lower the focal length, the higher the power.
◦ Formula: P = 1/f (where f is in metres).
◦ SI Unit: Dioptre (D). A lens with a focal length of one metre has a power of one dioptre (1 D).
◦ Sign interpretation:
▪ Negative power: Concave lens.
▪ Positive power: Convex lens.
• Applications of Lenses: Spectacles, simple microscope, compound microscope, telescope.
• Compound Microscope: Used to magnify micro objects.
◦ Main parts: Objective lens (close to the object) and Eyepiece lens (through which image is observed).
◦ Objective: Shorter focal length. Forms a large, real, inverted image of the object (placed between Fo and 2Fo) beyond 2Fo.
◦ Eyepiece: Longer focal length than objective. Forms a large and virtual image (uses the objective's image as its object, positioned between its optic centre and Fe).
• Refracting Telescope: Instruments to see distant objects clearly.
◦ Main parts: Objective lens and Eyepiece lens.
◦ Objective: Longer focal length and larger aperture. Forms a small, real, and inverted image of a distant object.
◦ Eyepiece: Shorter focal length and smaller aperture. Forms a virtual image (observes the image formed by the objective).
3. The World of Colours and Vision
• Refraction through a Glass Prism: When light rays enter and leave a prism, they deviate towards the base of the prism due to refraction.
• Dispersion of Light: The phenomenon of splitting up of a composite light into its component colours.
◦ Example: Sunlight splitting into colours when passing through a prism.
◦ Spectrum: The orderly arrangement of the component colours in white light.
◦ Order of colours (decreasing deviation, increasing wavelength): VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, Red).
◦ Deviation and Wavelength: The extent of deviation depends on the wavelength of light. Red deviates the least (longest wavelength), and Violet deviates the most (shortest wavelength).
◦ Factors affecting deviation: Refractive index of the medium, Wavelength of the colour of light.
• Rainbow: Formed as a result of the combined effect of refraction, dispersion, and internal reflection of sunlight within water droplets.
◦ A ray of sunlight undergoes refraction twice and internal reflection once inside a water droplet.
◦ Always formed in a direction opposite to the sun.
• Recombination of Colours: Dispersed colours can be recombined to produce white light (e.g., using a second inverted prism or Newton's Colour Disc).
• Electromagnetic Spectrum: The orderly distribution of electromagnetic radiations.
◦ Components: Radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X-rays, gamma rays.
◦ They do not require a medium to travel and travel through vacuum at the speed of light (approx. 3 × 10⁸ m/s).
◦ Infrared radiation: Main reason for heat in Sun's rays.
◦ Ultraviolet radiation: Helps produce vitamin D in the body.
• Primary Colours of Light: Red, Green, and Blue (RGB). All other coloured lights can be created using them.
◦ Combinations: Red + Green = Yellow; Red + Blue = Magenta; Blue + Green = Cyan; Red + Green + Blue = White (of same intensity).
• Secondary Colours of Light: Formed by combining any two primary colours.
◦ Yellow, Cyan, Magenta.
• Complementary Colours: Pairs of colours that combine to produce white light.
◦ Example: Yellow (Red + Green) + Blue = White.
• Persistence of Vision: The visual experience of an object persists for about 1/16 of a second after the object is quickly removed from the field of vision.
◦ Examples: Seeing a ring of fire when a burning stick is whirled rapidly. Newton's colour disc appearing white when rotated fast.
• Colours of Transparent Objects (Filters): Transmit light of their own colour and their component colours from white light, and block other colours.
◦ A filter of secondary colour transmits light of its own colour and its component colours.
• Colours of Opaque Objects: We see an object in the colour of the light that is reflected from the object to our eyes.
◦ They reflect the colour of the object as well as colours associated with adjacent wavelengths. All other colours are absorbed.
◦ An opaque object of a secondary colour can reflect light of its colour and its component colours.
◦ A surface that reflects all colours will appear white in white light.
◦ A surface that absorbs all colours appears dark.
• Scattering of Light: The irregular and partial directional deviation of light when it encounters particles in a medium.
◦ The intensity of scattering depends on the size of the particles in the colloid. As particle size increases, scattering intensity increases.
◦ If particle size is greater than the wavelength of light, scattering will be the same for all colours.
◦ Blue Colour of the Sky: Violet, indigo, and blue colours (shorter wavelengths) in sunlight undergo more scattering when they encounter atmospheric particles. This scattered light spreads in the sky, making it appear blue.
◦ Colour of Setting and Rising Sun: Sun's rays travel a longer distance through the atmosphere. Shorter wavelengths are scattered away, leaving red, yellow, and orange (longer wavelengths) to reach the observer's eye.
◦ Tyndall Effect: When light rays pass through a colloidal liquid or suspension, they get scattered, causing tiny particles to become illuminated, making the path of light visible.
• Eye and Vision:
◦ Power of Accommodation: The ability of the eye to change the curvature of the lens and adjust the focal length so that the image of the object always falls on the retina, regardless of the object's position.
▪ Enabled by ciliary muscles changing lens curvature and focal length. When ciliary muscles contract, curvature increases, focal length decreases.
◦ Least Distance of Distinct Vision (Near Point): The nearest point at which an object can be seen clearly. For healthy eyes, it's about 25 cm.
◦ Far Point: The farthest point at which an object can be seen clearly. This distance is considered to be infinity.
◦ Short-sightedness (Myopia): People can see nearby objects clearly but not distant objects.
▪ Cause: Eyeball is larger or power of the lens is more. Image forms in front of the retina.
▪ Rectification: Using a concave lens with suitable power.
◦ Long-sightedness (Hypermetropia): People can see distant objects clearly but not nearby objects clearly.
▪ Cause: Eyeball is smaller or power of the lens is less. Image forms behind the retina. Near point is more than 25 cm.
▪ Rectification: Using a convex lens with suitable power.
◦ Presbyopia: For older people, the distance to the near point may be more than 25 cm due to decreased efficiency of ciliary muscles and less power of accommodation.
• Light Pollution: The creation of artificial light in excessive amounts and intensity, harming natural habitats and human health.
◦ Consequences: Difficulty during night drive, obstructing astronomical observations, misleading migratory birds.
◦ Photoperiodism: Biological clock in plants (controlled by phytochrome) identifying the amount of sunlight received to control blooming, fruiting, and leaf shedding. Affected by light pollution.
4. Magnetic Effect of Electric Current
• Magnetic Effect of Electricity: A magnetic field is formed around a current carrying conductor, and this magnetic field can exert a force on a magnetic needle. This was discovered by Hans Christian Oersted in 1820.
◦ The direction of deflection of a magnetic needle depends on the direction of the current.
• Magnetic Field Lines: Imaginary lines used to visualise a magnetic field.
◦ Direction outside a magnet: North pole to South pole.
◦ Direction inside a magnet: South pole to North pole.
• Right Hand Thumb Rule: Imagine holding a conductor with your right hand such that the thumb points in the direction of the electric current, the fingers curled around the conductor will indicate the direction of the magnetic field.
• Ampere's Swimming Rule: An alternative rule: Imagine a person swimming in the direction of the electric current, looking at the magnetic needle. The north pole of the magnetic needle will deflect towards the left side of the person.
• Factors Affecting Magnetic Strength of a Coil (or Solenoid):
◦ Number of turns of the conductor (per unit length for solenoid).
◦ Strength of the electric current.
◦ Nature of the core material (e.g., soft iron core significantly increases strength).
◦ Area of cross-section of the core.
• Solenoid: An insulated conductor wound in a spiral shape (like a spring) where the centres of all turns lie on the same straight line.
◦ The magnetic field lines around a current-carrying solenoid are alike to those around a bar magnet.
• Right Hand Rule for Solenoid: If you hold a current carrying solenoid with your right hand such that your four fingers curl the coils in the direction of the current, the thumb points towards the north pole of the solenoid.
◦ If current is clockwise at an end, it's a South pole. If current is anticlockwise, it's a North pole.
• Electromagnets: Devices that create a magnetic field using electricity.
◦ Comparison with Bar Magnet:
▪ Bar magnet: Magnetism is permanent, polarity cannot be changed, magnetic strength cannot be varied.
▪ Current carrying solenoid (Electromagnet): Magnetism is temporary (only when current flows), polarity can be changed (by reversing current), magnetic strength can be varied.
◦ Applications of Strong Electromagnets: MRI scanning (patients remove metal objects due to strong magnetic fields), Maglev trains, Electric motors, Cranes.
• Force on a Current Carrying Conductor in a Magnetic Field:
◦ A current carrying conductor placed in a magnetic field experiences a force, causing it to deflect.
◦ Factors influencing the direction of the force: Direction of electric current and Direction of the magnetic field.
◦ If the direction of the current or the magnetic field is reversed, the direction of motion of the conductor will be reversed.
◦ If both the current and magnetic field directions are reversed together, the conductor will move in the same direction as before.
◦ The directions of the electric current, magnetic field, and the force experienced are mutually perpendicular.
• Fleming’s Left Hand Rule: Used to find the direction of motion (force) of a conductor in devices that utilise the magnetic effect of electricity.
◦ Hold the thumb, first finger, and second finger of your left hand perpendicular to each other.
◦ If the First finger points in the direction of the magnetic Field.
◦ And the seCond finger points in the direction of the electric current.
◦ Then the thuMb will indicate the direction of the force experienced by the conductor.
• Motor Principle: A current carrying conductor which is free to move, placed in a magnetic field, exhibits a tendency to deflect.
• Electric Motor: A device that converts electric energy into mechanical energy based on the motor principle.
◦ Main Parts:
▪ Magnetic Poles (N, S): Provide the magnetic field.
▪ Armature (ABCD): Coil of insulated copper wire wound over a soft iron core, attached to the axis.
▪ Axis of Rotation (PQ): Allows the armature to rotate freely.
▪ Split Rings (R1, R2): Part of the commutator.
▪ Graphite Brushes (B1, B2): Make electrical contact with the split rings.
◦ Working: Forces are experienced in opposite directions on the sides of the armature (AB and CD) due to the current and magnetic field, causing rotation.
◦ Split Ring Commutator: A mechanism used to change the direction of the current through the armature sides (AB and CD) after each half rotation (180°). This ensures the armature rotates continuously in the same direction.
◦ BLDC Motor (Brushless Direct Current Motor): Operates without brushes and split rings, using an electronic switch instead to change current direction. More energy efficient.
• Moving Coil Loudspeaker: Converts electric signals (audio signals) into sound waves. Energy conversion: Electrical energy to mechanical energy (vibration) to sound energy.
◦ Main Parts:
▪ Voice Coil: Placed in a magnetic field, receives audio signals.
▪ Field Magnet: Provides the magnetic field.
▪ Paper Diaphragm: Connected to the voice coil.
◦ Working: Audio signals pass through the voice coil, causing it to experience a force and vibrate (based on motor principle). This vibration causes the diaphragm to vibrate, reproducing sound.
