Science Hub

Concept: A concave lens is thinner at the center and thicker at the edges.

Reason: When a parallel beam of light falls on it, the lens refracts the light rays outwards (away from the principal axis). Since the rays spread out or "diverge" after passing through, it is called a Diverging Lens.

Statement: The heat (H) produced in a resistor is:
1. Directly proportional to the square of current (I²).
2. Directly proportional to the resistance (R).
3. Directly proportional to the time (t) current flows.

Formula: H = I²Rt

Imagine holding a current-carrying straight conductor in your right hand:

• If the Thumb points in the direction of Current.
• Then the Wrapped Fingers show the direction of Magnetic Field lines.

Definition: A reaction in which two or more reactants combine to form a single new product.

Example (Burning Coal):
C(s) + O₂(g) → CO₂(g)

Distilled Water: It is a pure covalent compound with no free ions. Hence, no conduction.

Rain Water: It dissolves gases like CO₂ and SO₂ from air to form carbonic/sulphuric acid. These acids dissociate into ions (H⁺), which conduct electricity.

Process: Heating sulphide ores strongly in the presence of excess air to convert them into oxides.

Reaction:
2ZnS + 3O₂ → 2ZnO + 2SO₂ (Heat)

Structure: Villi are finger-like projections on the inner wall of the small intestine.

Function: They increase surface area for maximum absorption of digested food into the blood. They are richly supplied with blood vessels.

Artificial Kidney: Dialysis (Hemodialysis) is a medical procedure used to remove nitrogenous wastes (urea) and excess fluid from the blood when a person's kidneys are not functioning properly.

A neurotransmitter is a chemical messenger (e.g., Acetylcholine) that carries signals across the synapse (gap) from the axon tip of one neuron to the dendrite of the next neuron.

1. Myopia (Near-sightedness):
A person can see nearby objects clearly but distant objects appear blurry.
* Causes: Excessive curvature of eye lens (high power) or elongation of the eyeball.
* Image Formation: Image forms *in front* of the retina.
* Correction: By using a Concave Lens of suitable power.

2. Hypermetropia (Far-sightedness):
A person can see distant objects clearly but nearby objects appear blurry.
* Causes: Focal length of eye lens is too long or eyeball becomes too small.
* Image Formation: Image forms *behind* the retina.
* Correction: By using a Convex Lens.

Principle: An electric motor works on the principle that when a current-carrying coil is placed in a magnetic field, it experiences a force (Lorentz force) that rotates it.

Construction:
1. Armature: A rectangular coil (ABCD).
2. Field Magnet: Strong permanent magnet.
3. Split Ring (Commutator): Reverses current direction every half rotation.
4. Brushes: Carbon brushes pass current to the ring.

Working: Current flows ABCD. Force on arm AB is downward, CD is upward (Fleming’s Left Hand Rule). The coil rotates anti-clockwise. The commutator reverses current, maintaining continuous rotation.

Let three resistors R₁, R₂, R₃ be connected in series.
Key Concept: Current (I) is same, Voltage (V) divides.

Total Voltage V = V₁ + V₂ + V₃ ... (i)
According to Ohm's Law (V=IR):
V₁ = I R₁
V₂ = I R₂
V₃ = I R₃

Substituting in (i):
IR_eq = IR₁ + IR₂ + IR₃
Taking I common and cancelling:
R_eq = R₁ + R₂ + R₃

Dispersion: The splitting of white light into its component colors (seven colors) when passing through a transparent medium like a prism is called dispersion.

Cause: Different colors have different speeds in glass. Red bends the least, Violet bends the most.

Spectrum: The band of seven colors obtained on a screen is called a Spectrum. The sequence is VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, Red).

Ohm's Law: At constant temperature, the current (I) flowing through a conductor is directly proportional to the potential difference (V) across its ends.
V = IR

Experimental Verification:
1. Set up a circuit with a resistor, ammeter (series), voltmeter (parallel), battery, and rheostat.
2. Vary the current using the rheostat and note readings of I and V.
3. Plot a graph of V vs I.
4. Result: The graph is a straight line passing through the origin, proving V/I is constant (R).

Solenoid: A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder.

Behavior:
* When current flows, magnetic field lines inside are parallel straight lines (uniform field).
* One end acts as the North Pole and the other as the South Pole.
* It behaves exactly like a bar magnet. The strength can be increased by inserting a soft iron core (Electromagnet).

Object Position: At Centre of Curvature (C).
Ray Diagram Logic:
1. Ray parallel to principal axis → passes through Focus (F).
2. Ray passing through Focus → becomes parallel to axis.
3. Intersection occurs exactly at C.

Nature of Image: Real, Inverted, and Same Size as the object.

Structure of Soap: A soap molecule has two ends:
1. Hydrophilic Head: Ionic end (dissolves in water).
2. Hydrophobic Tail: Carbon chain (dissolves in oil/dirt).

Mechanism:
* When soap is in water, the molecules arrange in a cluster called a Micelle.
* The tails stick to the oily dirt (center), and heads face outward into the water.
* Agitation pulls the dirt out in the form of an emulsion, washing it away.

Chemical Name: Calcium Sulphate Hemihydrate (CaSO₄·½H₂O).

Preparation: Heating Gypsum at 373 K (100°C).
CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O

Uses:
1. Setting fractured bones (Medical).
2. Making toys and statues.
3. Making surfaces smooth before painting.

Metals	Non-Metals
Form Basic Oxides (e.g., MgO).	Form Acidic/Neutral Oxides (e.g., SO₂).
Lose electrons (Electropositive).	Gain electrons (Electronegative).
React with dilute acids to give H₂.	Do not react with dilute acids.

Definition: A series of carbon compounds that have the same functional group and similar chemical properties.

Characteristics:
1. Successive members differ by -CH₂- group.
2. They differ in molecular mass by 14u.
3. They have similar chemical properties but graduating physical properties.
Example: Alkanes (Methane CH₄, Ethane C₂H₆).

Setup:
* Anode: Impure Copper block.
* Cathode: Thin strip of Pure Copper.
* Electrolyte: Copper Sulphate (CuSO₄) solution.

Process: On passing current, pure Cu from Anode dissolves into electrolyte and deposits on the Cathode. Impurities settle at the bottom as 'Anode Mud'.

Formula: CaOCl₂ (Calcium Oxychloride).

Preparation: By the action of Chlorine gas on dry slaked lime.
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

Uses: Bleaching cotton/linen, disinfecting drinking water, oxidizing agent.

1. With Sodium (Na):
Ethanol reacts to form Sodium Ethoxide and Hydrogen gas.
2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂↑

2. Dehydration (Hot Conc. H₂SO₄ at 443K):
Ethanol loses water to form Ethene (Unsaturated hydrocarbon).
C₂H₅OH → CH₂=CH₂ + H₂O

[Diagram Required in Exam]
The alimentary canal consists of Mouth, Oesophagus, Stomach, Small Intestine, Large Intestine.

Role of Stomach:
* The stomach walls secrete Gastric Juice containing:
1. HCl: Kills bacteria and makes medium acidic for enzyme action.
2. Pepsin: Breaks down proteins into simpler molecules.
3. Mucus: Protects the stomach lining from acid.

Amoeba is unicellular. Steps of nutrition:
1. Ingestion: It extends finger-like Pseudopodia to engulf food forming a Food Vacuole.
2. Digestion: Enzymes enter the vacuole and break down food.
3. Absorption: Digested food diffuses into the cytoplasm.
4. Assimilation: Used for energy and growth.
5. Egestion: Undigested residue is expelled by cell membrane rupture.

Nephron is the structural and functional filtration unit of the Kidney.

Structure:
* Bowman’s Capsule: Cup-shaped end containing Glomerulus (capillary bunch).
* Tubular Part: PCT, Henle’s Loop, DCT, Collecting Duct.

Function (Urine Formation):
1. Filtration: Blood is filtered in Bowman's capsule.
2. Reabsorption: Useful substances (glucose, water) are reabsorbed in the tubule.
3. Secretion: Wastes are added to forming urine.

Aerobic	Anaerobic
Occurs in presence of Oxygen.	Occurs in absence of Oxygen.
Complete breakdown of glucose.	Partial breakdown.
End products: CO₂, H₂O, Energy.	End products: Ethanol/Lactic Acid, CO₂.
Releases large energy (38 ATP).	Releases less energy (2 ATP).

Blood passes through the heart twice in one complete cycle.

1. Pulmonary Circulation: Deoxygenated blood moves from Right Ventricle → Lungs → Left Atrium (gets Oxygenated).
2. Systemic Circulation: Oxygenated blood moves from Left Ventricle → Body Organs → Right Atrium (gets Deoxygenated).

Significance: It prevents mixing of oxygenated and deoxygenated blood, ensuring high energy supply.

[Diagram Required]
Main Parts:
1. Sepals: Green leaf-like parts protecting the bud.
2. Petals: Colorful parts to attract insects.
3. Stamen (Male): Consists of Anther (pollen) and Filament.
4. Pistil/Carpel (Female): Consists of Stigma (sticky top), Style (tube), and Ovary (base containing ovules).

Law: In a cross between two parents pure for contrasting traits, only one form of the trait (Dominant) appears in the F1 generation, while the other (Recessive) remains hidden.

Example (Tall vs Dwarf):
Parents: TT (Tall) x tt (Short)
F1 Generation: All Tt (Tall).
Here, Tallness is dominant over shortness.

Sex determination is genetic.
* Male: XY chromosomes. Produces two types of sperms (50% X, 50% Y).
* Female: XX chromosomes. Produces only X type eggs.

Process:
* If sperm carrying X fertilizes egg (X) → Girl (XX).
* If sperm carrying Y fertilizes egg (X) → Boy (XY).
Thus, the father determines the sex of the child.

Reflex Arc: The pathway taken by nerve impulses in a reflex action (sudden involuntary response).

Path:
1. Receptor: Detects stimulus (e.g., Heat).
2. Sensory Neuron: Carries signal to Spinal Cord.
3. Relay Neuron: Processes signal in Spinal Cord.
4. Motor Neuron: Carries signal to muscle.
5. Effector: Muscle contracts (Hand withdraws).