" Hereditary and evolution" class 10th

 Topics to be covered

• Introduction
• What is Heredity?
• Inherited traits
• Mendel's experiments
• Laws of Inheritance
• Sex determination
• Evolution
• - Variations & its relation to Evolution
• Acquired vs. Inherited traits
• - Speciation
• -Evolution by stages
• Human evolution

What is Heredity?

• Passing of traits from parents/ancestors to offspring
• Genetics :- The branch of science which deal with the study of heredity

Heredity vs. Inheritance

Heredity

• The process by which characters are transferred from one generation to the next generation is called inheritance / heredity 
• The differences in traits of individuals of a progeny from each other and from their parents are called variations
• The branch of science which deals with inheritance and variation is called genetics

Inherited trait:

A trait that is genetically passed down from one generation to another

Inherited traits: Examples

Hair colour

. Eye colour

. Height

Shape of feet

. Ear lobes

How do the traits get inherited?

1. Mendel's Experiment

• Gregor Johann Mendel (1822-1884) is known as 'Father of Genetics'.
• Mendel performed his experiments with garden pea plant (Pisum sativum)
• He conducted artificial pollination/cross-pollination experiments using several true-breeding varieties having contrasting traits 
• He observed one trait at a time
• He hybridised plants with alternate forms of a single trait (Monohybrid cross). The seeds thus produced were grown to develop into plants of first filial generation (F₁) 
• Mendel then self-pollinated the F, plants to generate plants of second filial generation (F₂)
• Later, Mendel also crossed pea plants that differed in two characters (Dihybrid cross)

2. Mendel's Experimental Plant

Mendel selected garden pea as his experimental material because of the following reasons.

(1) It is an annual plant with a short life-cycle. So, several generations can be studied within a short period.

(2) It has perfect bisexual flowers containing both male and female parts

(3) The flowers are predominantly self-pollmating It is easy to get pure line for several generations.

(4) It is easy to cross-pollmate them because pollens from one plant can be introduced to the stigma of another plant by removing the anthers

(5) Pea plant produces a large number of seeds in one generation

(6) Pea plants could easily be raised, maintained and handled

 (7) A number of easily detectable contrasting characterstraits were available

3. Mendel's Observations

(1) F1 progenies always resembled one of the parents and trait of other parent was not seen

(2) F2 stage expressed both the parental traits in the proportion 3.1.

(3) The contrasting traits did not show any blending at either F1or F2 stage.

 (4) In dihybrid cross, he got identical results as in monohybrid cross

(5) He found that the phenotypes in F2 generation appeared in the ratio 3:1

(6) He found that the genotypic ration in F2 generation appeared in the ratio 1:2:1

4. Mendel's Laws of Inheritance

■ Based on his hybridisation experiments, Mendel proposed the laws of inheritance.

(i) Law of dominance (First law)

■ This law states that when two alternative forms alleles are present in an organism, only one factor expresses itself in F1 progeny and is called dominant while the other that remains masked is called recessive.

(ii) Law of segregation (Second law)

■ This law states that alleles of a pair segregate from each other during gamete formation, such that a gamete receives only one of the two factors. They do not show any blending.

iii) Law of independent assortment

According to this law the two factors of each character separate out independent of the factors of other characters at the time of gamete formation and get randomly rearranged in the offsprings producing both parental and new combinations of characters.

Sex Determination Mechanism :- 

Finalisation of sex at the time of zygote formation is called sex Determination .

XX-XY type :- 

Seen in many insects including humans .

Males have X and Y chromosomes along with autosomes and female have a pair of X chromosomes.

"Magnetic effect of electric current" class 10

 Topics to be covered:- 

• History of magnetism 
• Bar magnet 
• Magnety field
• Operated 's experiment 
• Magnetic field lines
• Magnetic field due to current carrying conductor due to magnetic field
• Electric motor 
• Electromagnetic induction
• Electric generator

Introduction:-

• Nail  attracted towards magnet.
• Refrigerator locked due to magnetic properties
• Metro doors use magnetism
• Electric motors and generators works on magnetism

Story of magnetism:- 

• Shepherd found some rocks that was attracted nail.
• People thought that rocks were magical and so called those rocks magnesia (word from magic)
• Later scientists give it a name magnetism.

Bar magnet:-

• Rectangular object that has a magnetic field .

Properties of bar magnet:-

• Align itself in the north south direction when suspended freely.
• North and South pole cannot be isolated.
• Like led repel and unlike poles attract .

• Not all materials are attracted by magnet.

Magnetic field::

• Region around a magnet where the magnet exerts its influence.

Magnetic field lines:- 

• Magnetic field is a vector quantity [magnitude + direction]
• Visual realization of magnetic field by bar magnet and iron filling experiment.
• Directions:- outside magnet:- North to South and Inside magnet:- South to North

Properties of magnetic field lines :-

• Form continuous closed loops
•  Tangent to magnetic field line at a given point specifies the direction of net magnetic field at that point
• Greater number of magnetic field lines per unit area stronger the magnetic field .
• Two magnetic field lines never intersect each other . If they do so that means it shows two directions at one point which is not possible. 

Operated experiment:- 

• Electricity and magnetism are very closely related .
• Operated observed the inter relation between electricity and magnetism.

Oersted experiment:- 

Observations:- 

• Magnetic compass needle deflected when current passes through a wire.
• A wire carrying electric current behave like a magnet.
• Deflection reverses as the direction of current is reversed.

Conclusion:- 

• A wire carrying electric current behave like a magnet.
• Moving charges produce a magnetic field in the surrounding region.

Magnetic field due to a current carrying 

• Straight conductor 
• Circular loop
• Solenoid

Magnetic field due to a current carrying straight conductor:-

• Magnitude of magnetic field produced at a given point increases as the current through the wire increases. 
• Magnetic field produced by a given current in a conductor decreases as the distance of the point from it increases.

Pattern of field lines:- 

• Concentric circles represent magnetic field around a current carrying straight wire.

Directions of magnetic field:- 

Right hand thumb rule :- If a current carrying straight conductor is held in your right hand such that thumb point towards the direction of current, then the wrapped fingers show direction of magnetic field lines.

Magnetic field due to a current carrying circular loop:-

• Every point on the wire carrying current would give rise to magnetic field appearing as straight lines at the centre of loop 

So

•  magnetic field is directly proportional to current 
• magnetic field is directly proportional to number of turns ,
• magnetic field is inversely proportional to square of distance 

Strength of magnetic field at the centre of coil (loop) depends upon:- 

Radius of coil:-

• Strength of magnetic field is inversely proportional to radius of coil . If radius increases, magnetic strength at the centre decreases.

Number of turns in the coil:- 

• As the number of turns in the coil increases , the magnetic field strength at the centre increases. This is because current in each circular turn is having the same direction thus field due to each turn add up .

The strength of current flowing in the coil:- 

• As the strength increases, the strength of magnetic field increases.

Maxwell Corkscrew Rule/ Right Hand rule:-

•  If we considered ourselves driving a corkscrew in the direction of current, then the direction of corkscrew is the direction of magnetic field.

Magnetic field due to a current carrying solenoid :-

• Solenoid is a coil wound into a tightly packed helix .
• Or 
• A coil of many circular turns of insulated copper wire wrapped in shape of cylinder.
• Field lines of a solenoid are similar to those of bar magnet.
• Field is uniform inside the solenoid.
• Strength of magnetic field is proportional to number of turns and magnitude of current.

Where do we use solenoid:- 

• Transformer creation

Electromagnet:- 

• Strong magnetic field produced inside the solenoid is used to magnetize the magnetic material like steel , soft iron , when placed inside the coil 

Magnetic field :- 

• Introduction of force due to magnetic field:- 
• A current carrying rod experiences a force perpendicular to its length and magnetic field 
• Direction of the force on the conductor depends upon:-
• - Direction of current and 
• - Directions of magnetic field

Fleming Left hand rule:-

Stretch your thumb , forefinger and middle finger of your left hand in such a way that they are mutually perpendicular to each other. If the first finger shows the direction of magnetic field and middle finger show the direction of current then the thumb will show the direction of motion of conductor.

Fleming ' left hand rule demonstration:- 

A relationship between direction of magnetic field, current and the force on the conductor .

Note :- downward :- inward

Upward:- outward

Application:- magnetic field and force exerted by it:- 

• Electric motor ,
• Electric generator
• Loudspeaker,
• Microphone,
• Measuring instruments etc.

Magnetism in medicine

• An electric current always produces a magnetic field. 
• Even weak ion currents that travel along the nerve cells in our body produce magnetic fields. 
• When we touch something, our nerves carry an electric impulse to the muscles we need to use. 
• This impulse produces a temporary magnetic field.
•  These fields are very weak and are about one-billionth of the earth's magnetic field. 
• Two main organs in the human body where the magnetic field produced is significant, are the heart and the brain. 
• The magnetic field inside the body forms the basis of obtaining the images of different body parts.
•  This is done using a technique called Magnetic Resonance Imaging (MRI). 
• Analysis of these images helps in medical diagnosis. 

• Magnetism has, thus got important uses in medicine.

ELECTRIC MOTOR

An electric motor is a rotating device that converts electrical energy to mechanical energy,

 Electric motor is used as an important component in electric fans, refrigerators, mixers, washing machines, computers, MP3 players etc. 

Material requirements:- 

Rectangular coil, magnetic poles , split rings. Axle, brushes and source battery.

Construction:-

An electric motor,  consists of a rectangular coil ABCD of insulated copper wire. 

The coil is placed between the two poles of a magnetic field such that the arm AB and CD are perpendicular to the direction of the magnetic field. 

The ends of the coil are connected to the two halves P and Q of a split ring. 

The inner sides of these halves are insulated and attached to an axle. 

The external conducting edges of P and Q touch two conducting stationary brushes X and Y, respectively, 

Working of electric motor:- 

Current in the coil ABCD enters from the Source battery through conducting brush X and flows back to the battery through brush Y. 

 current in arm AB of the coil flows from A to B. 

In arm CD it flows from C to D, that is, opposite to the direction of current through arm AB.

 On applying Fleming's left hand rule for the direction of force on a current-carrying conductor in a magnetic field .

 We find that the force acting on arm AB pushes it downwards while the force acting on arm CD pushes it upwards. 

Thus the coil and the axle O, mounted free to turn about an axis, rotate anti-clockwise. 

After half rotation. Q makes contact with the brush X and P with brush Y. 

Therefore the current in the coil gets reversed and flows along the path DCBA. 

A device that reverses the direction of flow of current through a circuit is called a commutator. 

In electric motors, the split ring acts as a commutator. 

The reversal of current also reverses the direction of force acting on the two arms AB and CD.

 Thus the arm AB of the coil that was earlier pushed down is now pushed up and the arm CD previously pushed up is now pushed down. 

Therefore the coil and the axle rotate half a turn more in the same direction. 

The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil and to the axle.

Significance of split rings :- 

• Act as a commutator .
• Commutator is a devise that reverses the direction of flowe of current 
• Reversal of current results in a continuous rotation of coil.

The commercial motors use (i) an electromagnet in place of permanent magnet: (i) large number of turns of the conducting wire in the current carrying coil; and (iii) a soft iron core on which the coil is wound. 

The soft iron core, on which the coil is wound, plus the coils, is called an armature. This enhances the power of the motor. 

Electromagnetic induction:- Process by which changing magnetic field in a conductor induced current in another conductor.

Application:- electric generator, Wireless charger , elevators, metro trains

1. Faraday 's Experiment 1 

Observations:-

• Relative motion between magnet and coil induced electric current in the coil 

2. Faraday 's Experiment 2

Observations:- 

• Relative motion between coil induce electric current.

3. Faraday 's Experiment 3

Observations:-

• Relative motion is not an absolute requirement for inducing current.

Faraday 's  Law of induction:-

First law:- 

• An EMF is induced in circuit whenever the amount of magnetic flux (no. Of magnetic field lines per unit area) linked with a circuit changes.

Second law:- 

• Magnitude of induced EMF in a circuit is equal to time rate of change of magnetic flux through the circuit.

Methods of producing induced EMF:- 

• Varying magnetic field (B)
• Varying area(A)
• Varying relative orientation of coil and magnetic field,

Direction of induced current:-

Fleming 's right hand rule:- 

• Stretch the thumb forefinger and middle finger of right hand so that they are perpendicular to each other . If forefinger indicates the Direction of magnetic field , thumb shows the direction of motion of current then the middle finger will show the Direction of induced current. This is Fleming right hand rule.

* Electric Generator:- 

• Device that convert mechanical energy into electric energy

-Principle Based on Electromagnetic Indrection

•  It says that current is  induced in coil /loop through change in its orientation or a change in its effective area.

Types of Electric Generator :-

• AC Generator
• DC Generator

 AC Generator =

• Alternating current is produced which changes its direction after equal intervals  of time

DC Generator:- 

• Direct current is produced which does not changes its direction with time.

- Construction AC Generator:-

• Rectangular coll induced copper
• Magnetic poles
• split rings.
• Axle
• Brushes
• • Galvanometer

* working of Electric generator :- 

• When the axle attached to two rings is  rolated such that arm AB moves up & CD moves down in the magnetic Field produced by permanent magnet, It rolates the coil clockwise
• By applying Fleming's & right hand, the induced current flows in  direction ABCD
•  Thus in external circult, current flows from B₂ to B₁
• After half a rotation.arm CD starts moving up & AB moving down. 
• As a result induced current in both arms changes, giving rise to net induced current in direction DCBA
• Now in External circuit , current flows from B1 to B2.
• Thus after half a rotation, polarity of current in respective arms changes.
• such a current which changes its direction. after equal intervals of time is called alternating current
• This device is called AC Generator

Note :-If there are larger numbers of turns in  the coil, the current generated in each turn adds up to give large current through coil.

DC Generator - Working

• split ring commutator is used to ensure unidirections flow of current.
•  with this, one brush is at all times contact with arm moving down.
•  This generator is thus called a DC generator

Difference the AC & DC

• DC flows in one direction always

 •Ac flows by reverses its directions periodically

• AC Changes direction after every 1/100 sec. Frequency of AC is 50 Hz

• AC Can transmitted over  long distance without much loss of energy.

Domestic electric current:- 

• In our homes, we receive supply of electric power through a main supply (also called mains), either supported through overhead electric poles or by underground cables.
• For safe conduction , we use 3 coated wire,
•  One with red insulation cover, is called live wire (or positive).
•  Second wire, with black insulation, is called neutral wire (or negative). 
• And third with green coat called earth wire.
• In our country, the potential difference between the two is 220 V.

At the meter-board in the house, these wires pass into an electricity meter through a main fuse. 

Through the main switch they are connected to the live wires in the house. 

These wires supply electricity to separate circuits within the house. 

Often, two separate circuits are used, one of 15 A current rating for appliances with higher power ratings such as geysers, air coolers, etc. 

The other circuit is of 5 A current rating for bulbs, fans, etc. 

Functions of green wire:-

• The earth wire, which has insulation of green colour, is usually connected to a metal plate deep in the earth near the house. 
• This is used as a safety measure, especially for those appliances that have a metallic body, for example, electric press, toaster, table fan. refrigerator, etc.
•  The metallic body is connected to the earth wire, which provides a low-resistance conducting path for the current. 
• Thus, it ensures that any leakage of current to the metallic body of the appliance keeps its potential to that of the earth, and the user may not get a severe electric shock.

Fuse:-

• Electric fuse is an important component of all domestic circuits. 
• It is a safety device which prevents the damage to appliances and the circuit due to overloading.. 
• Overloading can occur when the live wire and the neutral wire come into direct contact. (This occurs when the insulation of wires is damaged or there is a fault in the appliance.)
•  In such a situation, the current in the circuit abruptly increases. 
• This is called short-circuiting.

 The use of an electric fuse prevents the electric circuit and the appliance from a possible damage by stopping the flow of unduly high electric current. 

The Joule heating that takes place in the fuse melts it to break the electric circuit.

 Overloading can also occur due to an accidental hike in the supply voltage.

 Sometimes overloading is caused by connecting too many appliances to a single socket.

Thank you...

-