CBSE Pathshala

 Q1. Define light year. Ans. Light year is the distance travelled by the light in one year. Q2. Name the star nearest to the earth after sun. Ans. Proxima centuari. Q3. Why do stars shine? Ans. Stars are giant ball of gases in space that shine through the darkness and are held together by the force of gravitation. These gasses are hydrogen and helium. Some of the hydrogen is converted into  helium. A star shines due to this reaction nit’s core releasing energy that radiates into the outer space. Q4. What are constellations? Ans. Group of stars that make an imaginary shape in the night sky is called constellations. There are 88 constellations known so far. Examples ursa major, Ursa Minor, Orion, Aries cancer, Cassiopeia, Gemini,  Leo. Q5. Write short note on pole star. Ans. Pole star rises in the east at night and sets in the west in the early morning. Pole star is situated above the axis of rotation of the earth, so it appears stationary from the ear...

MIRROR FORMULA The relation between object distance(u), image distance(v) and the focal length (f) of the mirror is known as MIRROR FORMULA. Consider a concave mirror MM' (of small aperture). An object AB of height h is placed on the left of the mirror beyond its center of curvature so that the image formed is real, inverted and diminished in size(height = h'). Here : Object distance = PB = -u Image distance = PB'= -v Focal length = PF = -f Radius of curvature = PC = -R As shown in Figure, Δ ABP ∼ Δ A'B'P. ∴ A'B'/AB = PB'/PB ∴ A'B'/AB = (-v)/(-u) ∴ A'B'/AB = v/u.............(I) Similarly, as shown in the figure, Δ ABC ∼ Δ A'B'C. ∴ A'B'/AB = CB'/CB ∴ A'B'/AB = (PC-PB')/(PB-PC)........[as CB'=(PC-PB') and CB=(PB-PC)] ∴ A'B'/AB = [-R - (-v)]/[-u - (-R)] ∴ A'B'/AB = (-R + v)/(-u + R)........(II) By (I) & (II), v/u = (-R + v)/(-u + R) ∴ -...

Nutrition in plants 1.      The components that are necessary for our body are called (   ) a.      Vitamins b.      Pulses c.         Nutrients d.      Minerals 2.      The mode of nutrition in which organisms make food themselves from simple substances is called(   ) a.        Autotrophic nutrition b.      Heterotrophic nutrition c.       Saprotrophic nutrition d.      All of the above 3.      Some organisms live together and share shelter and nutrients. This is called a.      Predation b.        Symbiotic relationship c.  ...