12 December 2014

Stars and The Solar System- Solved Questions with set of Question bank for Class 8th

Chapter: 17- Stars and The Solar System- Solved Question 
CBSE Pathshala: 
B1.What re the difference between stars and planets?
Ans:
Stars are:          a. luminous                   b. Stationary
Planets are :      a. Non luminous            b. Movable

B2. What re the difference between galaxy and constellation?
Ans: (i) The first difference is that a galaxy is a collection of billions of stars whereas a constellation is a collection of only a very few stars.

(ii) The second difference is that a galaxy does not form a definite pattern which resembles the shape of an animal or a human being but a constellation appears to resemble an animal or human being in its shape

B3. What are the asteroids?     
Answer: There is a large gap in between the orbits of the Mars and Jupiter. This gap is occupied by a large number of small bodies that revolve around the sun. These are called asteroids
B.4.What is meteorites? In which bodies are meteorites craters more commonly found and why?
Ans: meteorites are rocky bodies revolving around the sun. Large meteors when hit the surface of planet create craters. Meteorites craters more commonly found on those planets and moon which have no or little atmosphere to burn off the falling rocks. E.g. Moon and mercury.
B5. What is comet? How is its tail formed?
Ans:  Comet is small body of ice and dust revolving around the sun in its elongated orbit. When comet approaches the sun, it heats up and leaves behind a stream of hot glowing gases and dust particles. We see it as a tail.
B6. Why does geostationary satellite seem fixed above a point on the earth?
Ans: A satellite placed at about 3600 km above the equator completes one revolution around the sun in 24 hrs . This makes its position fixed above a point on the earth

B.7. why do other stars appear to move from east to west whereas the pole star appear to be stationary?
Ans: Pole star lies exactly above axis of the rotation of earth while other star does not. Therefore when earth rotates from west to east the star will appear to move from east to west to an observer on the earth but pole star appear stationary to same observer.
This property of pole star makes it useful to the sailors as they can locate north with the help of pole star
B8. Why Venus is hotter than mercury even if it is far away from the Sun?
Ans: Venus has highest percentage of CO2 in its atmosphere that result into greenhouse effect.
B9. why is mercury so hot during the day and cold at night?
Ans: Being close to sun, mercury turns extremely hot about 400 degree centigrade during day. As gravitational force is not enough to support hot atmosphere the temperature drops to - 200 degree centigrade.
B. 10. How far away is earth from the sun if sunlight takes 8.3 minutes to reach earth?
Ans: Time taken by sunlight to reach earth = 8.3 min = 498 sec
Speed of light = 3 x 10^8 m/s
Distance b/w earth and sun = 3 x 10^8 m/s x 498 sec = 1494 x 10^8 m

Chapter: 17- Stars and The Solar System- Question bank for Class VIII(8th)
1. Which is the smallest planet of the solar system?

2. Which is the nearest planet from the sun?

3. The planet which is called red planet is:

a. Saturn          b. mars            c. Venus                    d. Neptune

4. The star which appears stationary is:

a. Sirius             b. pole star      c. Andromeda        d. Orion

5. A group which forms definite pattern is called:

a. comet           b.constellation c. meteor                 d. meteoroid

6. What are celestial bodies?

7. What are known as phases of moon?

8. Why does moon show different phases?

9. Write the applications of artificial satellites

10. How would you locate pole star?

11. What is an orbit?

12. Which is the nearest star to us?

13. What is a satellite?

14. What makes the earth a special planet?

15. Why does earth appears blue-green from the space?

16. Name the inert planets

17. Name one outer planet.

18. What are asteroids?

19. Distinguish between a meteor and meteorite.

20. What is the tail of comet due to?

21. Draw a neat diagram of Ursa Major, Orion

22. How are artificial satellites different from natural satellites?

23. Name some artificial satellites launched by India.

24. On what days during a month can you see more stars in the sky? Give reasons.

25. What keeps the planets move around the sun in their orbits?
Stars and The Solar System
Stars and The Solar System Oral questions CCE FA Test
CBSE Ch. Stars and The Solar System (Physics) MCQ
Choose the Appropriate Answer MCQ
Test Paper Based on CCE (With Solution)
Questions Paper for SA with solution
Stars and The Solar System- Question bank for Class VIII(8th)

08 November 2014

Physics - Class 10 - to study refraction of light in rectangular glass slab

In triangle GBC, r1+90 =-r2+90 ...as the sum of angles in a triangle is 180 degree

r1=r2............................i

Now refractive index of glass=sin i/sin r1 =sin e/sin r2....................ii

as r1=r2 from (i)

so i=e .................iii

Now as the incident ray is extended till E, angle LDE should be equal to i.

For, CF and DE, and interceptor CD angle BCF(90+e)=angle CDE(90+i) and they are corresponding angle so CF parallel to DE.

1) A ray of light incident on one of the parallel faces of a rectangular glass slab, emerges out of the opposite parallel face

 a)      parallel to the incident ray but laterally displaced
b)      inclined to the incident ray
c)       along the same straight line as the incident ray
d)      gets absorbed into the body of the glass slab and does not emerge out of it

2) Four students reported the following observation tables for the experiment to trace the path of a ray of light passing through a glass slab for different angles of incidence. The observations, likely to be correct are those of student.

i
r
e

i
r
 e
30
40
30

30
20
30
40
50
40

 40
30
40
50
 60
 50

50
 40
50

(a)



(b)

i
r
e

i
r
 e
30
 20
 40

30
20
20
40
30
50

40
30
 30
50
40
60

50
 40
40
(c)




(d)



(a) A                     (b) B                      (c) C                       (d) D

3) Why does bending of light takes place ?

a)      Because light travels with same velocity in different media
b)      Because it travels with different velocity in different media
c)       None of these                

4) In which direction does a ray bend when it travels from a denser medium to a rarer medium :

a)      It bends away from the normal as it meets the surface of rarer medium
b)      It bends towards the normal as it meets the surface of rarer medium
c)       It goes straight 
d)      None of these

5) Refractive index is the property of :

a)      One medium
b)      The pair of media
c)       One vacuum
d)      None of these

6) Does the refractive index of substance change with the colour of light ?

a)      No, refractive index does not depend upon the colour of light (wavelength)
b)      Yes, refractive index depends upon the colour of light (wavelength)
c)       None of these

7) Give the example of total internal reflection :

a)      Mirage (Mrig Trishna), generally observed in deserts in summer
b)      Looming, generally observed in cold region
c)       Both of these

8) What is critical angle ?

a)      Critical angle is the angle of incidence for which angle of refraction is 45 degree when light travels from denser medium to rarer
b)      Is the angle of incidence for which angle of refraction is 90 when light travels from rarer to denser medium
c)       Is the angle of incidence for which angle of refraction is 90 when light travels from denser to rarer medium
d)      None of these

9) What is the advantage of "total internal reflection" over reflection ?

a)      Total internal reflection is an interesting phenomenon than reflection
b)      Loss of intensity of light is less in total internal reflection than reflection
c)       None of these

10) What do you mean by the statement "Refractive Index of glass is 1.5"

a)      It means refractive index of glass with respect to air is 1.5
b)      Refractive index of air with respect to glass is 1.5
c)       It means refractive index of glass with respect to water is 1.5
d)      None of these

Answer
1. [B]                   2.[B]              3. [B]                                4.[A]                      5.[B]                     

6. [B]                  7. [B]             8. [C]                                 9. [B]                   10. [A]



08 October 2014

8th Solved Chemical effects of electric current assignments

Q1. Do liquids also conduct electricity? Name two liquids which conduct electricity and two liquids which do not conduct electricity.

Ans: Two liquids which conduct electricity are : Lemon juice ,Vinegar, Tap water.
Two liquids which do not conduct electricity : Milk, Honey

Q2. Name a device which glows even when a weak electric current passes through it.

Ans: LED [Light Emitting Diode]

Q3.What is electrochemistry? 

Ans: Electrochemistry is defined as the branch of science that deals with chemical effect of electric current.

Q4. Which effect of electric current is utilized for detecting the flow of current through a solution:
a) When a torch bulb is used?    (b) When a compass is used?

Ans: (a) Heating effect              (b) Magnetic effect

Q5. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? .

Ans : No, This is because ordinary water is conductor of electricity and it will be fetal.

Q6. When electric current is passed through acidified water, then hydrogen and oxygen are formed. What type of effect of current is illustrated by this statement?

Ans: Chemical effect of current

Q7. State some of the characteristics of chemical changes brought about by the chemical effect of electric current.

Ans: (a) When electric current is passed through water, water dissociates into hydrogen and oxygen. Hydrogen is deposited over negative pole and oxygen is deposited over positive pole. Deposition of hydrogen and oxygen at different poles is visible in the form of bubbles.

(b) When electric current is passed through the solution of a metal salt, such as solution of copper sulphate, metal gets deposited at the negative pole, because metal is positively charged.

(c) Sometimes, the colour of solution also changes when electric current passes through it.

Q8. Name the metal which is usually electroplated on car parts such as bumpers and  bicycle handlebars made of steel.

Ans: Chromium

Q9. An iron key is to be electroplated with copper. Draw a labeled sketch of the experimental set up used for this purpose.

Ans: Iron rod made as cathode and copper rod as anode and dipped into copper sulphate electrolyte.

Credit: www.brighthubengineering.com
When current passes through copper sulphate split up into ions Cu+2 and SO4-2 Cu+2  move towards catode to gain electron and neutralize as cu and form layer over iron. Copper as anode losse electron and form  Cu+2 move to electrolyte to form CuSO4

Q10. Name two metals which are usually electroplated on cheaper metals for making jewellery (or ornaments).

Ans:chromium and silver and Gold

Q11. You are required to do electroplating of copper on an iron object. Name the positive electrode (anode) and  the electrolyte you will use for this purpose.


Ans: Copper as anode and cathode as a cathode and CuSO4 as electrolyte

Q12. During electroplating the copper deposited on the plate connected to negative terminal comes from the solution. How this loss of copper from solution compensated?

Ans:  From the other plate an equal amount of copper gets dissolved in the  solution. Thus the loss of copper from the solution gets compensated and the process keeps going. This means that copper gets transferred from one plate to another.

Q13. Why does compass needle show more deflection when you test sea water, compared to ordinary water?

Ans: Sea water is more conductor compared to ordinary water as they contain lot of dissolved salt 

Q15. Describe electrolysis of water?

Ans: When electricity passes through water it splits up into H+ and O- ions. H+ move toward cathode to gain electrons to became H2 and  O- move towards anode to lose electrons to became O2

Reduction at cathode: 2 H+(aq) + 2e → H2(g)

Oxidation at anode: 2 H2O(l) → O2(g) + 4 H+(aq) + 4e

Q16. What happens to the needle of a magnetic compass kept nearby when electric current is switched on in a wire? Why does this happen?

Ans:  The needle of a magnetic compass shows deflection when  kept nearby a wire caring current
 as wire behave like a magnet

Q17 Iron is used in bridges and  automobile to provide strength. Which metal is electroplated on iron to protect it from corrosion?

Ans: iron is plated with nickel, chromium, tin, zinc, or cadmium.
Iron used in constructing a building is coated with a layer of zinc. This protects iron from corrosion and rusting.

Q18. We should never handle electrical appliances with wet hands or while standing on a wet floor. Why?

Ans : This is because water  conduct electric current to body and we get shock as water is good conductor.

Q19. When the free ends of a conductivity tester (made by using a battery connected to a wire wound around a compass) are dipped into the following solution, then in which solution or solutions the compass needle shows deflection. 
Solutions are: Lemon juice, Vinegar, Tap water, Vegetable oil, milk, Honey.

Ans: Lemon juice, Vinegar, Tap water.

Q20.Why does an electric bulb glow when a current passes through it?

Ans:The bulb glows because the electricity which is a form of energy which heats a wire inside of the bulb as it passes through. This gives a glow to the wire which is magnified by the curve of a bulb.

Solution for Basic Science Publication Bharati Bhawan  [Central public School]

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