• General ways of preventing infection are:

Public hygiene is one basic key to the prevention of infectious disease. In the method of prevention of diseases, following practices are adopted:

1. To avoid exposure to air-borne microbes, adopt living conditions that are not overcrowded.
2. To prevent exposure to water-borne microbes, safe drinking water should be provided.
3. To avoid vector-borne infections, we can provide clean environment as it would not allow mosquito breeding.

• Specific way of preventing infections:

The specific ways relate to a peculiar property of the immune system that usually fights off microbial infections. During smallpox epidemics, it was noted that people who survived after suffering from smallpox, did not get infected with it again. Such observations led to the birth of immunization, which is a specific method of preventing infectious diseases.

When the immune system first sees an infectious microbe, it responds against it and then remembers it specifically. So the next time that particular microbe, or its close relatives enter the body, the immune system responds with even greater vigour. This eliminates the infection even more quickly than the first time around. This is the basis of the principle of immunization.

Vaccines work on the principle of immunization. Vaccines help a body's immune system prepare in advance to fight infectious illnesses and potentially deadly diseases caused by infectious agents or their by-products. Vaccines ‘fool’ the immune system into developing a memory for a particular infection by putting something that mimics the microbe we want to vaccinate against, into the body. Many such vaccines are now available for preventing a number of infectious diseases, and provide a disease-specific means of prevention like tetanus, diphtheria, whooping cough, measles and polio.

Amplitude: It is a measure of the loudness or softness of the sound. The magnitude of the maximum disturbance in the medium on either side of the mean value is called Amplitude of the wave, represented by the letter A.

difference between colloidal solution, solution and suspension.

December 20, 2019<a href="https://www.toppr.com/">Toppr</a>

Let us consider a binary mixture of A and B. let the number of moles of A and B bee nA and nB respectively, then

xA = nA/(nA+nB)

xB = nB/(nA+nB)

Here, xA+xB = nA/(nA+nB) + nB/(nA+nB)

xA+xB = 1.

The sum of the mole fractions of all the components in binary solution system must be equal to unity.

Yes , smell is not a matter , and the smell of perfume is also not a matter but the particles in air of the perfume is matter . When a particle of perfume is inhaled by our nose is causes a pleasant sensation in our nose thus causing smell, buy that sensation is not a matter, the matter is that particle floating in air

Although the Rutherford atomic model was based on experimental observations it failed to explain certain things.

• 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.

Many people would not know but liquids, including the humble water actually boils not due to the fact that we heat it but actually because when you heat water or any other liquid, it's pressure vis-a-vis atmospheric pressure changes.
In order to raise the boiling point of a liquid without adding anything in it, we can increase the pressure around the liquid, this can delay the boiling of the liquid and elevate the boiling point.
This is why in hill stations, it takes longer to cook or boil water, because the atmospheric pressure there is higher

Rutherford used gold for his scattering experiment because gold is the most malleable metal and he wanted the thinnest layer as possible.

The gold sheet used was around 1000 atoms thick.

Therefore, Rutherford selected a Gold foil in his alpha scatttering experiment.

Consider a body of mass m initially at rest. If on application of force F, it travels a distance s, then

Work done, W = F x s

By Newton's second law, F = ma

W = ma x s

where, a = acceleration

Using equation of motion v² - u² =2as, we get

(v²-u²)/2 = as

W = m x (v² - u²)/2

As intial velocity is zero, W =  ½mv²

This work done is stored as kinetic energy of the object.

So, KE = ½  mv²

The places on a sound scientific footing by the duo scientists write were like the phenomenon of motion places.

This was mainly being developed by Galileo Galilei and Sir Isaac Newton.

These are some of the best experiments that are now being done in the history of science and further followed by these experiments.

Helicobacter pylori  causes peptic ulcers.

A group of atoms carrying a charge is known as polyatomic ion, example of polyatomic cation: NH₄⁺ and polyatomic anion: NO₃^-.

Velocity = frequency x wavelength

Given data:

Frequency = 1000 Hz

Wavelength = 34 cm 34/100 = 0.34 m

Velocity = 1000 Hz x 0.34 m

Velocity = 340 ms-1

Distance = 1000 m

Formula of velocity  

Velocity = distance / time

Time = distance / velocity

Time, t = 1000 m / 340 ms-1

t =  2.94 seconds

Atomic mass of carbon is 12 hydrogen is 1 and oxygen is 16.

So the molecular mass of C₂H₅OH = 24 + 5 + 16 + 1 = 46 unit..

Atomic mass of magnesium is 24 sulphur is 32 and oxygen is 16.

So the molecular mass of MgSO₄ = 24 + 32 + 64 = 120 unit

Na is symbol of normal sodium atom which have 11 protons in nucleus , with electronic configuration (2,8,1) having total 11 electrons in its all 3 shells. in this condition because nucleus have 11 protons, it have 11 unit positive charge and because of 11 electrons it have 11 unit negative charge . Because of equal number of positive charge and negative charge they cancel each other . that's why normal sodium atom (Na) is electrically neutral. But Na+ is positive ion of sodium. during chemical reaction sodium atom (Na) loses his one electron present last orbit. because only one electron is present in its last orbit , it is 3rd orbit . by losing this electron 3rd orbit loses its existence and second orbit having 8 electrons become outermost orbit and in this way it becomes stable. But now this atom have 10 electrons that is 10 negative charge and 11 protons that is 11 positive charge. in this condition number of positive charge is 1 unit more than negative charge . that's why sodium atom get unit positive change and sodium single positive (Na+) ion forms.

A complex tissue consist of more than one type of cells having a common origin which coordinate to perform a common function. Xylem and phloem are called complex tissues as, they are made up of different types of cells. Xylem is composed of four different types of cells (elements), namely (i) tracheids (ii)vessels (iii) xylem parenchyma (iv) xylem sclerenchyma (or fibre) Phloem is also composed of four different types of elements (i) sieve tubes (ii) companion cells (iii) phloem parenchyma (iv)phloem fibre T

Aerosol: When particles of solid or liquid dispersed in gaseous medium, the mixture is known as Aerosol. For example – cloud, smog, smoke etc.

Emulsion: Colloidal solution is called emulsion, when dispersing medium and dispersed phase both are liquid. For example – milk, butter, face cream, etc.