Why is the distance between stars expressed in light years? What do you understand by the statement that a star is eight light years away from the Earth?
Stars at a distance of millions of kilometers from the earth. Thus, there large distance are expressed in the light year. One light year is the distance travelled in one year.
One light year = 9.46 x 1012 km.
If a star is located eight years away from the earth that means the distance between the star and the earth is equal to the distance which is travelled by light in eight years. So, the distance between the star and the earth us given by:
8 x (9.46 x 1012) km = 7.6 x 1012 km.
What is a constellation? Name any two constellations.
Explain how you can locate the Pole Star with the help of Ursa Major.
Draw sketches to show the relative positions of prominent stars in
(a) Ursa Major and (b) Orion
Boojho made the following sketch (Fig. 17.29) of the solar system. Is the sketch correct? If not, correct it.
Name two objects other than planets which are members of the solar system.
Phases of the moon occur because
(a) we can see only that part of the moon which reflects light towards us.
(b) our distance from the moon keeps changing.
(c) the shadow of the Earth covers only a part of moon’s surface.
(d) the thickness of the moon’s atmosphere is not constant.
The radius of Jupiter is 11 times the radius of the Earth. Calculate the ratio of the volumes of Jupiter and the Earth. How many Earths can Jupiter accomodate?
Do all the stars in the sky move? Explain.
In which part of the sky can you find Venus if it is visible as an evening star?
Mark the following statements as true (T) or false (F):
(a) Pole Star is a member of the solar system. ( )
(b) Mercury is the smallest planet of the solar system. ( )
(c) Uranus is the farthest planet in the solar system. ( )
(d) INSAT is an artificial satellite. ( )
(e) There are nine planets in the solar system. ( )
(f) Constellation Orion can be seen only with a telescope. ( )
Which of the following can be beaten into thin sheets?
(a) Zinc (b) Phosphorus (c) Sulphur (d) Oxygen
Fill in the blanks
(a) Most liquids that conduct electricity are solutions of , ______________ and ______________.
(b) The passage of an electric current through a solution causes ______________ effects.
(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the terminal of the battery.
(d) The process of depositing a layer ofany desired metal on another material by means of electricity is called .
Give two examples each of situations in which you push or pull to change the state of motion of objects.
Fill in the blanks:
(a) Friction opposes the _____________ between the surfaces in contact with each other.
(b) Friction depends on the _____________ of surfaces. (c) Friction produces __________.
(d) Sprinkling of powder on the carrom board ________ friction.
(e) Sliding friction is ___________ than the static friction.
List conditions under which combustion can take place.
Indicate whether the following statements are True (T) or False (F).
(a) Unicellular organisms have one-celled body. (T/F)
(b) Muscle cells are branched. (T/F)
(c) The basic living unit of an organism is an organ. (T/F)
(d) Amoeba has irregular shape. (T/F)
Which of the following cannot be charged easily by friction?
(a) A plastic scale
(b) A copper rod
(c) An inflated balloon
(d) A woollen cloth.
Fill in the blanks:
(a) A place where animals are protected in their natural habitat is called .
(b) Species found only in a particular area is known as .
(c) Migratory birds fly to far away places because of changes.
Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room. Explain.
What are the different ways in which water gets contaminated ?
Which of the following cannot be charged easily by friction?
(a) A plastic scale
(b) A copper rod
(c) An inflated balloon
(d) A woollen cloth.
Give reasons for the following:
(a) Aluminium foils are used to wrap food items.
(b) Immersion rods heating liquids are made up of metallic substances.
(c) Copper cannot displace zinc from its salt solution.
(d) Sodium and potassium are stored in kerosene.
Describe the threat to the beauty of the Taj Mahal.
Explain the process of formation of petroleum.
Differentiate between internal fertilization and external fertilization.
What is menstruation? Explain.
How are test tube babies born?
Describe an activity to show that the incident ray, the reflected ray and the normal at the point of incidence lie in the same plane.
Fill in the blanks:
(a) Microorganisms can be seen with the help of a ____________.
(b) Blue green algae fix __________ directly from air to enhance fertility of soil.
(c) Alcohol is produced with the help of __________.
(d) Cholera is caused by __________.
Boojho stands at A just on the side of a plane mirror as shown in Fig. 16.20. Can he see himself in the mirror? Also can he see the image of objects situated at P, Q and R?