Class 8 Cbse Ncert Revision Question's1) When a ball pen refill is rubbed vigorously against polythene, it attractssmall pieces of paper. What makes the refill attract paper?2) Write the use of an electroscope. 3) Explain the purification of copper using electrolysis with the help of anelectric circuit. 4) Write any two uses of electrolysis. 5) Why are multiple images formed when two mirrors are placed at rightangles to each other?6) Why should we not stand under a tree when there is thunder andlightning?7) We electroplate metals with chromium to make car parts, bath taps, kitchen gas burners etc. Why is chromium itself not used for makingthese materials?8) Describe the chemical effect of current on water with the help of adiagram. 9)Paheli wants to deposit silver on an iron spoon. She took silver nitrate(AgNO3) solution in a beaker and set up a simple circuit forelectroplating. Which terminal of the battery should the spoon beconnected to? What material should the other electrode be made of?10) An electric current is passed through a conducting solution. List anythree possible observations. 11) What happens to light when it gets dispersed? Give an example. 12) How are the eyes of the day birds different from night birds?

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as we know our atmosphere or air have different levels. every level has other gasses, and every gas has another permeability. when the light comes from lower permeability to higher permeability, it changes its direction. so that means that when the light comes from the moon to the earth, it changes it's direction many more times. it basically means that the shape of the light part of the moon is changed on the earth.

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force is based upon mass and acceleration.the statement is not always true.

it can be explained from newton's second law of motion.

as per newton's second law of motion the rate of change of momentum is directly proportional to the applied force and takes place along the direction of force.

mathematically it can be written as -

                                              ⇒      

here   k is the proportionality constant whose value is 1.

                                                            [a is the acceleration=dv/dt]

hence we see that force not only depends on mass and acceleration but also on velocity and rate of change of mass. force f will depend on mass and acceleration only when mass is constant.

hence the statement that force is based upon mass and acceleration is false.

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