For the following statements, write T for True and F for False.
(a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons.
(b) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.
(c) The mass of an electron is about 1/2000 times that of proton.
(d) An isotope of iodine is used for making tincture iodine, which is used as a medicine.
Put tick (✓) against correct choice and cross (✕) against wrong choice in questions 15, 16 and 17.
(a) False
(b) False
(c) True
(d) False
If number of electrons in an atom is 8 and number of protons is also 8, then (i) what is the atomic number of the atom? and (ii) what is the charge on the atom?
With the help of Table 4.1, find out the mass number of oxygen and sulphur atom.
For the symbol H,D and T tabulate three sub-atomic particles found in each of them.
Explain with examples (i) Atomic number, (ii) Mass number, (iii) Isotopes and iv) Isobars. Give any two uses of isotopes.
Define valency by taking examples of silicon and oxygen.
The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes 168 X and 188 X in the sample?
Describe Bohr’s model of the atom.
Draw a sketch of Bohr’s model of an atom with three shells.
Write the electronic configuration of any one pair of isotopes and isobars.
Na+ has completely filled K and L shells. Explain.
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
State any two conditions essential for good health.
How is our atmosphere different from the atmospheres on Venus and Mars?
Who discovered cells, and how?
Explain any one method of crop production which ensures high yield.
Compare the use of manure and fertilizers in maintaining soil fertility.
The following is the distance-time table of an object in motion:
Time in seconds Distance in metres
0 0
1 1
2 8
3 27
4 64
5 125
6 216
7 343
(a) What conclusion can you draw about the acceleration? Is it constant, increasing, decreasing, or zero?
(b) What do you infer about the forces acting on the object?
Why does a desert cooler cool better on a hot dry day?
How does the water kept in an earthen pot (matka) become cool during summer?
A stone is released from the top of a tower of height 19.6 m. Calculate its final velocity.
An athlete completes one round of a circular track of diameter 200 m in 40 s. What will be the distance covered and the displacement at the end of 2 minutes 20 s?
What do you mean by acceleration due to gravity?
Explain, why is it difficult for a fireman to hold a hose, which ejects large amounts of water at a high velocity.
A train starting from a railway station and moving with uniform acceleration attains a speed 40 km h-1 in 10 minutes. Find its acceleration.