10th Class Physical Sciences – Page 10

Q. Why does we get dew on the surface of cold soft drink bottle kept in open air?
A: It is because of condensation of water molecules in the air on the surface of cold drink bottle.
1. When the water molecules in air, during their motion strike the surface of cold soft drink bottle, they loose their kinetic energy.
2. When the water molecules loose their energy their temperature falls down and so they condense as water droplets on the surface of the
bottle.

Q. Why do stars appear twinkling?
A: We view the stars from earth through thick layers of turbulent air of the earth’s atmosphere.
1. The light from the stars reach the viewer after passing through these layers of air. It is refracted many times in random directions.
2. These random refractions make the star to appear twinkling to the viewer.
3. A viewer cannot experience this type of vision of twinkling if he could see the stars beyond the atmosphere of the earth.

Q. How do you appreciate the role of Fermat principle in drawing ray diagrams?
A: According to Fermat’s principle that light selects the shortest path to travel.
1. This is the reason for the propagation of light in straightlines.
2. We use this principle, when we draw ray diagrams to find the image of an object formed by mirrors to illustrate the laws of reflection, refraction etc.

Q: What are optically denser and rarer media?
A : Let V1 and V2 be the speed of light in the two given media respectively.
1. If V1 > V2 then the first medium is denser medium and the second medium is rarer medium.
2. If V2 > V1 then the second medium is denser medium and the first medium is rarer medium.

Q: Suppose you are inside the water in a swimming pool near an edge. A friend is standing on the edge. Do you find your friend taller or shorter than his usual height?
A : The friend seems to be taller than his actual height.
1. This is because the light ray travels from a rarer medium (air) to denser medium gets refraction and bends towards the normal.
2. This seems to be coming from a distant point for the swimmer. So the person appears taller than his usual height.

Practice Questions – 10th Physical Science.
1 . The focal length of a converging lens is 20 cm. An object is 60 cm. from the lens. Where will the image be formed and what kind of image is it?
2. If a white sheet of paper is stained with oil, the paper turns transparent. Why?
3. What do you mean by power of a lens?
4. Why is the sky blue?
5. Why does the picture appear distorted when a bar magnet is brought close to the screen of a television.
6. Give few applications of Faraday’s law of induction in our daily life.
7. What is the magnetic force on the charge moving parallel to a magnetic field?
8. List three metals that are found in nature in uncombined form?
9. What is the difference between roasting and Calcination. Give one example for each.
10. How many water molecules are present in the following ores:
a) Bauxite b) Epsom salt c) Gypsum d) Carnallite.
11. Give an example for esterification reaction?
12. Suggest a chemical to distinguish between ethanol and ethanoic acid and explain the procedure.
13. What is soap?
14: State and explain Hund’s rule taking the configuration of carbon as an example.
15: What is an electromagnetic spectrum? Give a familiar example for it.

Q: How do the values of electron gain enthalpy change in a group, in a period and in metals? (2 Marks)

A: Electron gain enthalpy values decrease as we go down in a group, but increase along a period from left to right.
Metals have very low electron gain enthalpy values and alkaline earth
metals have even positive values.
Note that the negative sign for energy value in table indicates that energy is liberated or lost, and the positive sign tells that the energy is gained or absorbed.
All the factors which influence the ionization energy would also influence the electron gain enthalpy.

Q: Explain the term ‘electronegativity’. What factors influence it?

A: The electronegativity of an element is defined as the relative tendency of its atom to attract electrons towards it self when it is bonded to the atom of another element.
All the factors that influence the ionization energy and the electron affinity of elements influence the electronegativity values of these elements.
Because of this, Millikon proposed that the electronegativity of an element is the average value of its ionization energy and electron affinity.
Electronegativity = Ionization energy + electron affinity / 2

Q: How does the value of electronegativity vary as we go down a group or across a period? (2 Marks)

A: Electronegativity values of elements decrease as we go down in a group and increase along a period from left to right.
The most electronegative element is ‘F’. and the least electronegative stable element is ‘Cs’.

Q: Write a note on the properties of ‘metals’ and ‘non – metals’. (4 Marks)

A: Metals generally show less electronegative character. In compounds, they generally show a tendency to remain as positive ions.
This property is often termed as electropositive character. Metals are electropositive elements.
Non metals are generally more electronegative due to their smaller atomic radii.
Let us examine the elements of 3rd period.
3rd period: Na Mg Al Si P S Cl.
We know that Na and Mg are metals; Al and Si are semi metals (metalloids); P, S and Cl are non metals. So we find metals on left side and non metals on right side of the periodic table.
This metallic character decreases while non metallic character increases as we move along a period (from left to right)

Let us take group 14 (IV A) elements.
IV A group: C Si Ge Sn Pb
Here also we know that carbon is non metal, Si and Ge are metalloids, Sn and Pb are metals.
So we find non metals particularly at the right hand side top and metals at the left and right hand side bottom of the periodic table.
This means metallic character increases while non metallic character
decreases in a group as we move from top to bottom.

AP 10th Class Physical Science – 2 Marks Practice Questions with Answers 2016

10th Class Physics Important Questions – Elements Chapter – For AP and Telangana