CBSE Class 10 - Science

Students may confuse that in absence of moisture and air will also makes metals to corrode

It is to be noted that under the presence of air and moisture only metals will corrode

Rust is a brown covering that forms on iron substance when it comes in sustained contact with air and moisture. The process of forming rust is called rusting.

Activity

For illustrating the process of rusting we need to prove that a bunch of iron nails rusts when there is both moisture and oxygen and it doesn’t rust when there is an absence of either moisture or oxygen.

Take three test tubes that can be closed properly. In the first test tube keep partially submerged iron nails. In the second test tube keep iron nails fully submerged in water with a layer of oil separating the water and air in the test tube. In the third test tube keep iron nails with some amounts of anhydrous calcium chloride.

Observe these test tubes for 3 weeks. And these are the results.

The first test tube that has got abundant amounts of air and moisture will have rusted iron nails. The second test tube that has abundant moisture but with no access to air hence the iron nails will not have rust. The third test tube has anhydrous calcium chloride and this absorbs all the moisture in the air. Hence the third test tube will have abundance of air, but no moisture. The iron nails in the third test tube also will not have rust. Hence only the test tube with air and moisture gathers rust on the iron nails. Test tubes that provides only one of air or moisture doesn’t provide an atmosphere for the iron nails to rust.

Students may confuse regarding incomplete combustion of carbon and about pollution caused by synthetic detergents.

It is important to know regarding catenation of carbon, imcomplete combustion of carbon and effects synthetic detergents on environment.

(a)There are two specific reasons why carbon forms many number of compounds. They are

1.Catenation - Carbon has this unique ability to easily combine with other atoms of carbon in different combinations.

2.Carbon atoms have also got another unique ability to combine with other elements like nitrogen, oxygen, chlorine, bromine etc.

(b) Blackening is the phenomenon when unburnt carbon particles get attached to vessels. This occurs when the combustion is incomplete or not happening properly and gas is getting wasted.

Since carbon is being wasted due to incomplete combustion we have to adjust the air flow so that oxygen rich air allows the gas to burn completely. Hence air holes has to be adjusted to ensure that blackening doesn’t happen.

(c) Synthetic detergents are compounds that do not get decomposed by micro organisms. Or in other words detergents are not bio degradable and hence they stay in the water for a very long period as a pollutant.

A person with hypermetropia or long sight can see only distant objects clearly, not the nearby objects. This is because the image is formed behind the retina.

Draw the ray diagrams for hypermetropia and its correction.

Hypermetropia is a defect of vision. A person who has this defect can easily see objects far away but cannot see objects close by. This is caused due to

1. Change or reduction in the curvature of the lens.

2. Decrease in the size of the eyeball.

Remember: Current is same through all the resistors in a series circuit. Voltage applied across all the resistors is same in a parallel circuit.

There are only two resistors and they can be connected only in two ways: series and parallel. Minimum current will flow when the effective resistance is the highest. Maximum current will flow when the effective resistance is the lowest. Hence the current will be minimum in a series circuit and it will be maximum in a parallel circuit.

(a)

(i) For minimum current flow - the two resistors should be connected in series

(ii) For maximum current flow - The two resistors should be connected in parallel.

(b) Calculate the strength of the total current in the circuit in the two cases.

(i) Minimum current flowing

- Resistors connected in series

If the two resistors are connected in series,

Equivalent resistance = R = R₁ + R₂ = 5 + 10 = 15 Ω

According to Ohm's law V = IR. Substituting V = 6V and R = 15 Ω, we get I = 0.4 A

(ii) Maximum current flowing

-Resistors connected in parallel

If the two resistors are in parallel,

Equivalent resistance is calculated using $\frac{1}{R}$ = $\left(\frac{1}{R_1}+\frac{1}{R_2}\right)$

R = $\frac{5\times 10}{5+10}$ = $\frac{50}{15}$ = 3.3 Ω

We have V = IR.

Substituting V = 6 V and R = 3.3 Ω, we get I = 1.8 A

Origin of species and the particular function of the organ should not be misrelated.

The differences between analogous and homologous structures should be clearly explained along with examples.

Analogous organs like the name refers to, are those organs that have the same function but are different in structure and origin.

Homologous organs are those organs which have same basic structure and origin but perform different functions.

Wings of an insect and those of a bat are examples of analogous organs.

Forelimbs of frogs and those of a human are examples of homologous organs

Implantation is mistaken to be fertilisation process.

Reproductive system in humans, mechanism of reproduction should be known clearly.

(a)

(i)Implantation - It is the process by which the zygote, future embryo, formed by the fusion of sperm and egg nuclei travels down from the fallopian tubes to get embedded into the wall of uterus inside the female body.

(ii)Placenta - The placenta is a connection established by blood vascular tissue between foetus and the mother. It is significant in its role as the growing embryo receives nutrition and oxygen from the mother’s blood through placenta. Placenta is a vascular structure on the inner lining of the uterus which is connected to the umbilical cord of the foetus.

(b)Duration of pregnancy is termed to be gestation period. The average length of human gestation period is 280 days or 40 weeks or roughly 9 months.

Students may confuse while answering the trend of atomic size in groups and in periods. Also confuse at basis for Medeleev's classification as atomic number but actually atomic mass

Knowledge of Mendeleev's periodic table and atomic size in groups and periods makes easy to solve

a.Mendeleev used two criteria for classifying elements in the periodic table.

1. Atomic Mass - The elements in the periodic table are arranged according to the increasing order of their Atomic mass

2. The formulae of their hydrides and oxides were also used to classify them in the periodic table.

b.Mendeleevs periodic law is that that chemical properties of the elements are periodic functions of their atomic mass. That means the characteristics or properties get repeated periodically.

c.Hydrogen displayed both the property of alkali metals and halogens. Hydrogen like alkalis forms compound when it reacts with halogen, oxygen and sulphur. These reactions produces compounds that have a similar formulae when alkali metals react with these elements. So Mendeleev positioned Hydrogen in the first column above the Alkali metals in the table. At the same time, hydrogen, a diatomic molecule is a gas and can form covalent compounds like halogens. Hence Hydrogen can also be placed above the halogen group.

d.(i) From left to right the nuclear charge increases and hence the atomic size decreases. (ii) From top to bottom the atomic size increases as new rings are added to the atom.

Mark the arrows on the diagrams properly, following the right hand thumb rule.

(a) Write the definition of magnetic field and the method to draw magnetic field lines using a magnetic compass.

(b) State and explain right hand thumb rule with diagram.

(OR)

(a) Write about a solenoid with diagram. Draw the pattern of magnetic field lines around a current carrying solenoid.

(b) Find the direction of the magnetic field around a current carrying circular loop, placed flat on a table, using the right hand thumb rule.

(a) Magnetic field is the region around a magnet in which a magnetic material experiences a force because of that magnet.

The direction of magnetic field lines at a place can be determined by placing a magnetic compass in the field. The direction along which the magnetic needle of the compass aligns itself gives the direction of the magnetic field lines.

(b) We can obtain the magnetic field produced around a current carrying conductor by using the right hand thumb rule.

If you hold a current carrying conductor in your right hand in such a way that the thumb points towards the direction of current, the direction in which the fingers fold around the conductor will give the direction of the magnetic field.

OR

(a)

A solenoid is a coil of several circular turns of insulated conducting wire, wrapped closely in the shape of a cylinder.

(b) The direction of current inside the loop will be downwards and outside the loop will be upwards.

This is obtained using the right hand thumb rule that says if you hold a current carrying conductor in your right hand in such a way that the thumb points towards the direction of current, the direction in which the fingers fold around the conductor will give the direction of the magnetic field.

Spleen might be labelled as pancreas. Components of bile are wrongly considered to be enzymes.

OR

Urethra is a part belonging to both excretory and reproductive system. It should be labelled in both of the systems.

Diagram of digestive system and significance of bile in the process of digestion should be given.

OR

Labelled diagram of excretory system in humans, structure and significance of the kidney should be given.

(a)

(b) Bile does not contain any enzyme but it is essential for digestion due to following functions.

Bile is dark green or yellowish fluid secreted by the exocrine gland, liver. Bile contains bile salts that breakdown the larger fat molecules into smaller globules, called as emulsified fats. Bile juice also makes the acidic food entering the small intestine, alkaline for pancreatic and intestinal enzymes to act on it.

OR

(a)

(b) Kidneys serve as the main excretory organs in human beings. They play an important role in the removal of nitrogenous wastes from the body in the form of urine. They also maintain salt-water balance in the body by the process of reabsorption.