Explore & Learn

To know what wifi is, we need to learn about waves.

A wave is a disturbance in a medium that carries energy without a net movement of particles. Sound is an example of a wave.

There are two types of waves, Transverse and longitudinal.

Transverse wave-

A wave in which the medium vibrates at right angles to its propagation direction.

A ripple in water is an example; Light is also a transverse wave.

Longitudinal wave-

A wave vibrating in the direction of propagation.

Sound is a longitudinal wave. In a longitudinal wave, the Molecules, mostly air molecules, hit the molecules in front and create a compression and expansion state across the point from where it is created till the point it stops.

Reflection and refraction of waves-

Reflection-

Reflection is the bouncing back of light or sound when it hits a surface. When a light, for example, reflects, there are factors like Incident ray, reflected ray, angle of reflection, and angle of incident.

Refraction-

Refraction is the bending of a ray when it travels from one medium to another.

Optical fiber-

An optical fiber, or optical fiber, is a flexible glass or plastic fiber that can transmit light from one end to the other.

IN PROGRESS...

Latent heat is the energy absorbed or released by a substance during phase change without changing its temperature.

Types of Latent Heat:

1. Latent Heat of Fusion – The heat required to melt a solid into a liquid (or released when freezing).

2. Latent Heat of Vaporization – The heat required to boil a liquid into a gas (or released when condensing).

Why doesn't the temperature change:

When a substance undergoes a phase change, all the energy it absorbs (or releases) goes into breaking or forming molecular bonds, not into raising the temperature. That’s why ice at 0°C and water at 0°C have the same temperature but different energy levels.

Real-life applications:

• Sweating & Cooling:

  • Your sweat absorbs heat from your body and evaporates, taking away latent heat and cooling you down.

• Boiling Water & Steam Burns:

  • Steam at 100°C has more energy than boiling water at 100°C because it contains the latent heat of vaporization. That’s why steam burns are more severe than boiling water burns.

• Ice Packs in Medicine:

  • When ice melts, it absorbs heat from the body, reducing swelling.

• Refrigerators & Air Conditioners:

  • These work by compressing and expanding refrigerants, using latent heat to absorb heat from inside and release it outside.

• Weather & Hurricanes:

  • When water evaporates from oceans, it stores latent heat in water vapor. When this vapor condenses into clouds, it releases heat, fueling hurricanes.

Torque is the twisting force that tends to cause rotation.

• Direction of Torque:

  • If the force causes counterclockwise rotation, the torque is positive.

  • If the force causes clockwise rotation, the torque is negative.

• Units of Torque:

  • SI unit: Newton-meter (N·m)

  • CGS unit: Dyne-centimeter (dyne·cm)

• Conditions for Equilibrium:

  • For an object to be in rotational equilibrium, the net torque acting on it must be zero.

  • This means that the sum of all clockwise torques must equal the sum of all counterclockwise torques.

Examples of Torque in Daily Life:

• Opening a door by pushing the handle

• Using a wrench to tighten a bolt

• A seesaw balancing on a pivot

• Turning the steering wheel

Buoyancy

Buoyancy is the upward force exerted by a fluid (liquid or gas) on an object placed in it. This force acts opposite to gravity and is responsible for objects floating or sinking in a fluid.

• Fb​ = Buoyant force (N)

• ρ = Density of the fluid (kg/m³)

• g = Acceleration due to gravity (9.8 m/s²)

• V = Volume of fluid displaced (m³)

Real-Life Applications of Buoyancy:

• Ships and Boats: Designed to displace enough water to stay afloat.

• Hot Air Balloons: Rise because the hot air inside is less dense than the surrounding air.

• Submarines: Adjust their density using ballast tanks to float or sink.

• Hydrometers: Measure liquid density based on how high they float.

Terminal Velocity

Terminal velocity is the maximum constant speed an object reaches when falling through a fluid (such as air or water). It occurs when the downward force of gravity is balanced by the upward force of air resistance (drag), meaning there is no net acceleration.

Forces Acting on a Falling Object:

1. Gravity (Weight, W)

   • Acts downward, pulling the object toward the Earth.

   • Given by W=mg, where mmm is mass and g is acceleration due to gravity (9.8 m/s²).

2. Air Resistance (Drag Force, Fd)

   • Acts upward, opposing the motion.

   • Increases with speed until it equals weight.

How Terminal Velocity is Reached:

1. When an object first starts falling, gravity dominates, and the object accelerates downward.

2. As speed increases, air resistance also increases.

3. Eventually, air resistance grows equal to the object's weight, and net force becomes zero.

4. At this point, the object stops accelerating and continues falling at a constant velocity—this is called terminal velocity.

• vt​ = Terminal velocity (m/s)

• m = Mass of the object (kg)

• g = Acceleration due to gravity (9.8 m/s²)

• ρ = Density of the fluid (kg/m³)

• A = Cross-sectional area of the object (m²)

• Cd​ = Drag coefficient (depends on shape and surface texture)

Factors Affecting Terminal Velocity:

1. Mass of the Object: Heavier objects generally have higher terminal velocity.

2. Shape and Surface Area: A larger surface area increases air resistance, reducing terminal velocity.

3. Density of the Fluid: Falling through air vs. water changes terminal velocity (it’s much lower in water).

4. Drag Coefficient: Streamlined objects (like skydivers in a head-first position) have lower drag and higher terminal velocity.

Examples:

• Skydiving: A skydiver in a belly-down position has a terminal velocity of ~55 m/s (200 km/h), but in a head-down position, it can increase to ~90 m/s (324 km/h).

• Raindrops: They fall at terminal velocity (~9 m/s) due to air resistance, preventing them from causing damage.

• Parachutes: Increase air resistance dramatically, reducing terminal velocity and allowing safe landings.

Polymers are large molecules made up of repeating smaller units called monomers. These monomers are chemically bonded to form long chains or networks.

Types:

• Natural PolymersFound in nature. Examples:

  • Proteins (e.g., in skin and muscles)

  • Carbohydrates (e.g., starch, cellulose)

  • DNA (carries genetic information)

• Synthetic PolymersMan-made for various applications. Examples:

  • Plastic (e.g., polyethylene, PVC)

  • Rubber

  • Nylon and Teflon

Linear Polymers: Long, straight chains (e.g., PVC).

Branched Polymers: Chains with side branches (e.g., low-density polyethylene).

Cross-linked Polymers: Chains linked by bonds at various points (e.g., Bakelite).

Properties:

Flexible or Rigid depending on structure.

Resistant to chemicals.

Used in packaging, textiles, electronics, and more.

Chromatography is a technique used to separate and identify different components in a mixture. It works by making the different substances move at different speeds through a stationary phase while being carried by a mobile phase.

• Stationary Phase: The fixed material that the mixture moves through (e.g., paper, silica gel).

• Mobile Phase: The solvent that carries the mixture through the stationary phase (e.g., water, ethanol).

• Separation Principle: Different components move at different speeds based on their size, solubility, or affinity to the phases.

Types:

• Paper Chromatography:

  • Used for separating pigments, inks, or food dyes.

  • A drop of the mixture is placed on filter paper, and the solvent carries the components upward.

  • Different substances travel different distances.

• Thin Layer Chromatography (TLC):

  • Similar to paper chromatography but uses a glass plate coated with a thin layer of silica or alumina.

  • Provides faster and better separation.

• Gas Chromatography (GC):

  • Used for volatile substances.

  • A gas acts as the mobile phase, carrying the sample through a tube coated with the stationary phase.

• Liquid Chromatography (LC):

  • Used for non-volatile substances.

  • Often used in medical and drug testing.

Rf Value:

The Rf value helps identify the separated substances:

Rf = Distance moved by the solvent/Distance moved by the substance​

• Rf values are always less than 1.

• Each substance has a unique Rf value in a given solvent.