• Rutherford proposed that the electrons revolve around the nucleus in fixed paths called orbits. According to Maxwell, accelerated charged particles emit electromagnetic radiations and hence an electron revolving around the nucleus should emit electromagnetic radiation. This radiation would carry energy from the motion of the electron which would come at the cost of shrinking of orbits. Ultimately the electrons would collapse in the nucleus. Calculations have shown that as per Rutherford model an electron would collapse in the nucleus in less than 10-8 seconds. So Rutherford model was not in accordance with Maxwell’s theory and could not explain the stability of an atom.

• One of the drawbacks of the Rutherford model was also that he did not say anything about the arrangement of electrons in an atom which made his theory incomplete.

• Although the early atomic models were inaccurate and failed to explain certain experimental results, they were the base for future developments in the world of quantum mechanics.

Nanometre is a very, very small unit of measuring length. It is written as nm.
1 nanometre = 1/10⁹ metre
So, 1 nm = 10^-9 m

10^(-9)

let initial velocity = u & accleration is a then

distance travelled in 4 sec = S6

using , s = ut + at²/2

          S6 = 4u + a36/2

               =  6u+18a

distance covered in 2 sec = S2 = 2u + 4a/2

                                           =2u+2a = 200           (given)

                                       u+a = 100             ........................1

now distance covered in 2 to 6 sec is given 220cm

      S6-200 = 220

     6u + 18a = 420       

        u+3a = 70             .................2

from 1& 2

a = -15 & u=115

velocity after 7 sec = V7

       V₇ = u + at

           =115 - 15*7=10cm/sec
 

(i) Tea can be prepared by following steps:Take 100ml of water as solvent and boil it few minutes.
(ii) Now add one tea spoon sugar, one tea spoon tea leaves and 50ml of milk. Here sugar, tea leaves and milk are solute.
(iii) Now boil it again for few minutes so that sugar will dissolves in solution as sugar is soluble in water
(iv) Now filter the solution. Collect the filtrate in cup. The insoluble tea leaves will be left behind as residue.

Chordates: 
1. A notochord is present at some stage in the life of a chordate.
2. Central nervous system is dorsal and hollow.
3. Gill slits are present in the pharynx either in the embryo or adult.
4. Tail is present at some stage in the life of the chordate.
5. Heart is ventral.
6. If present RBCs contain respiratory pigment (haemoglobin). 

Non- chordates:
1. Notochord is not present at any stage in the life of a non-chordate.
2. Central nervous system is ventral and solid.
3. Gill slits are absent.
4. Tail is absent.
5. Heart is dorsal (if present).
6. If haemoglobin or other respiratory pigment is present, it is found in the blood plasma. RBCs are absent.

Sound is a type of energy. Sound travels in the form of wave from one place to another.

Sound is produced because of the vibration of any object. In other words, when an object is vibrated it produces sound.

When the slope of distance-time graph is a straight line parallel to time axis, the object is moving with uniform motion.

A quantity which has only magnitude but no direction is known as a scalar quantity.
Work is done only when a force produces motion.And it is the product of the force exerted on the the body and the distance moved by the body in the direction of force.
i.e. W =F.s
Work is actually the scalar product of force and displacement and hence is a scalar quantity.
W =F.s
i.e. W = Fs cos θ
where F is the force, s the displacement and θ the angle between force and displacement.  According to the angle θ, work can be positive, negative, or zero.
Work is the outcome of the force and displacement caused by the body.
Force and displacement are vector quantities (they have both magnitude and direction) and the dot product of two vector quantites always gives a scalar quantity. So work has only magnitude but not direction.

Work does not depend on direction is called a scalar quantity. It depends on magnitude only. Force and displacement is a vector quantity which depends on magnitude as well as direction both.

Following are the measures one should adopt to control air pollution:

Avoid Using Vehicles

People should avoid using vehicles for shorter distances. Rather they should prefer public modes of transport to travel from one place to another. This not only prevents pollution but also conserves energy.

Energy Conservation

A large number of fossil fuels are burnt to generate electricity. Therefore, do not forget to switch off the electrical appliances when not in use. Thus, you can save the environment at the individual level. Use of energy-efficient devices such CFLs also controls pollution to a greater level.

Use of Clean Energy Resources

The use of solar, wind and geothermal energies reduce air pollution at a larger level. Various countries including India have implemented the use of these resources as a step towards a cleaner environment.

Lithotripsy is a medical procedure involving the physical destruction of hardened masses like kidney stones, bezoars or gallstones.

Red Blood Cells

The Red blood cells are also called erythrocytes. RBCs store the haemoglobin, which is a respiratory pigment that binds to oxygen or carbon dioxide molecules. This helps in the transportation of the oxygen to different tissues and organs of the human body. It also takes away the carbon-dioxide from different organs and tissues to be replenished in the lungs.

Haemoglobin is mainly composed of iron, which combines with the oxygen, thus giving a reddish colour to the blood. It occupies 40-45% of the total volume of blood. The main function of the RBCs is the transportation of nutrients and the hormones throughout the human body.

White Blood cells

The white blood cells are also called Leukocytes. These cells act as a defence system against any infections in the human body. They produce a special kind of proteins called antibodies, which identify and fight against the foreign entities invading the human body. These cells are classified further as granulocytes and agranulocytes.

The white blood cells contain visible granule-like structures in the cell bodies, hence their names Granulocytes. On the other hand, agranulocytes do not possess these granule-like structures. The three kinds of granulocytes are neutrophils, basophils, and eosinophils. The two types of agranulocytes are lymphocytes and monocytes.

WBCs comprise 1% of the total blood volume. They are colourless because they are devoid of haemoglobin.

The continuous process by which nitrogen is exchanged between organisms and the environment is called nitrogen cycle. Nitrogen is an essential nutrient, needed to make amino acids and other important organic compounds, but most organisms cannot use free nitrogen, which is abundant as a gas in the atmosphere.

Nitrogen cycle involves the following steps:

(i) Nitrogen fixation: This process involves the conversion of atmospheric nitrogen into nitrates, which are soluble in water. This is done by various nitrogen fixing bacteria. Example - Rhizobium, blue green algae and bacterium Azotobacter.

(ii) Ammonification: It is the process of decomposing complex, dead organic matter into ammonia. This is done by microorganisms living in the soil.

(iii) Nitrification: It is the process of conversion of ammonia into nitrites and then into nitrates. This is done by nitrifying bacteria. Example - Nitrosomonas and Nitrobacter.

(iv) Denitrification: It is the process of reducing nitrates present in the soil to release nitrogen back into the atmosphere. Example - Pseudomonas.

<p><img src="https://i.imgur.com/OGOJoM7.jpg" /></p>

The decomposers help in decomposing the dead bodies of plants and animals, and hence act as cleansing agents of environment. The decomposers also help in putting back the various elements of which the dead plants and animals were made, back into the soil, air and water for reuse by the producers like crop-plants, e.g. the decomposers like purifying bacteria and fungi decompose the dead plants and animal bodies into ammonia. This ammonia is converted into nitrates by nitrifying bacteria present in soil. These nitrates act as fertilizer in the soil and are again absorbed by the plants for their growth. Thus, the nitrates act as fertilizer in the biosphere so that the process of life may go on and on like an unending chain.

Mass m = 30 kg  on Earth
weight = m g = m G M / R²
          G = universal gravitational constant
          M = mass of Earth
          R = Radius of Earth

mass of the body remains same on the surface of other planets.
gravity on a planet = g' = G M' / R' ²
                         M' = M/9        and  R' = R/2
     =>  g ' = G M/R * 4/9 = 4 g / 9
 
Weight on the planet = m g' = 4/9 m g  = 4/9 * 30 kg = 40/3  kg

When an object moves along a straight line with uniform acceleration, acceleration during motion and the distance covered by it in a certain time interval by a set of equations known as the equations of motion. Three equations of motion:

i. v  = u + at

ii. s  = ut + ½ at²

iii. 2as  = v² – u²

where u is the initial velocity of the object which moves with uniform acceleration a for time t, v is the final velocity, and s is the distance travelled by the object in time t.

• Sound intensity is a property of the sound source but loudness depends on the sound source, the medium and the receiver, as well.
• Sound intensity holds a small significance in problems involving human hearing system, but loudness is a very important property to consider in such problems.
• Sound intensity is measured in Watt per square meter whereas loudness is measured in Sones.