What is the greenhouse effect?
The greenhouse effect is the way in which heat is trapped close to the surface of the Earth by “greenhouse gases”. These heat - trapping gases can be thought of as a blanket wrapped around the Earth, which keeps it tastier than it without them. Greenhouse gases include carbon dioxide, methane and nitrous oxides. An increase in the content of such gases would lead to a situation of global warming.
List any three human activities that you think would lead to air pollution.
What causes winds?
Why is the atmosphere essential for life?
Why do organisms need water?
Why is water essential for life?
We know that many human activities lead to increasing levels of pollution of the air, water-bodies and soil. Do you think that isolating these activities to specific and limited areas would help in reducing pollution?
List any three human activities which would lead to an increase in the carbon dioxide content of air.
How does the atmosphere act as a blanket?
How is our atmosphere different from the atmospheres on Venus and Mars?
You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?
Which of the following has more inertia: (a) a rubber ball and a stone of the same size? (b) a bicycle and a train? (c) a five-rupees coin and a one-rupee coin?
State the universal law of gravitation.
Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.
A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force (Fig. 11.3). Let us take it that the force acts on the object through the displacement. What is the work done in this case?
What is meant by a pure substance?
How does the sound produced by a vibrating object in a medium reach your ear?
In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium observations are in agreement with the law of conservation of mass.
sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water
What are canal rays?
State any two conditions essential for good health.
Who discovered cells, and how?
Calculate the number of aluminium ions present in 0.051 g of aluminium oxide.
(Hint: The mass of an ion is the same as that of an atom of the same element. Atomic mass of Al = 27 u)
How much momentum will a dumb-bell of mass 10 kg transfer to the floor if it falls from a height of 80 cm? Take its downward acceleration to be 10 m s-2.
Why do we classify organisms?
Abdul, while driving to school, computes the average speed for his trip to be 20 km h-1. On his return trip along the same route, there is less traffic and the average speed is 40 km h-1. What is the average speed for Abdul’s trip?
According to the third law of motion when we push on an object, the object pushes back on us with an equal and opposite force. If the object is a massive truck parked along the roadside, it will probably not move. A student justifies this by answering that the two opposite and equal forces cancel each other. Comment on this logic and explain why the truck does not move.
Why is sound wave called a longitudinal wave?
State which of the following situations are possible and give an example for each of these:
(a) an object with a constant acceleration but with zero velocity
(b) an object moving in a certain direction with an acceleration in the perpendicular direction.
What do you mean by buoyancy?
Classify each of the following as a homogeneous or heterogeneous mixture.
soda water, wood, air, soil, vinegar, filtered tea.
How is a prokaryotic cell different from a eukaryotic cell?