class 9 science important question anser
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Q. Mention two uses of isotopes in the field of medicine.
Ans.
(i) An isotope of cobalt is used in the treatment of cancer.
(ii) An isotope of iodine is used in the treatment of goitre.
Q. Who discovered vaccine for the first time?
Ans.
Edward Jenner discovered vaccine for the first time.
Q. Why do fish go in deep waters during day light?
Ans.
During day time, the shallow water is warmer and hence contains less dissolved oxygen. Therefore fish tend to go in deep water during day time
Q. (a) Name two properties of a substance to check its purity?
(b) Alloys cannot be separated by physical means, though it is considered mixture, Why?
Ans.
(a) A pure substance has a fixed melting point or boiling point at constant pressure. The purity of a substance can be tested by checking its melting point or boiling point. If a substance is impure i.e. it contains traces of another substance, the melting and boiling point of that substance will change.
(b) Alloys are homogeneous mixtures of metals and cannot be separated into their components by physical methods. But still, an alloy is considered as a mixture because it shows the properties of its constituents and can have variable composition.
Q. Is it possible that an object is in the state of accelerated motion due to external force acting on it, but no work is being done by the force? Explain it with an example.
Ans.
Yes, it is possible, if an object is moving in a circular path because in that case the centripetal force always acts perpendicular to the direction of displacement.
For example: Consider the motion of earth around sun. The earth is constantly moving in a direction perpendicular to the gravitation pull of sun, hence work done by the gravitational force is zero.
hope it will help you
Q. Mention two uses of isotopes in the field of medicine.
Ans.
(i) An isotope of cobalt is used in the treatment of cancer.
(ii) An isotope of iodine is used in the treatment of goitre.
Q. Who discovered vaccine for the first time?
Ans.
Edward Jenner discovered vaccine for the first time.
Q. Why do fish go in deep waters during day light?
Ans.
During day time, the shallow water is warmer and hence contains less dissolved oxygen. Therefore fish tend to go in deep water during day time
Q. (a) Name two properties of a substance to check its purity?
(b) Alloys cannot be separated by physical means, though it is considered mixture, Why?
Ans.
(a) A pure substance has a fixed melting point or boiling point at constant pressure. The purity of a substance can be tested by checking its melting point or boiling point. If a substance is impure i.e. it contains traces of another substance, the melting and boiling point of that substance will change.
(b) Alloys are homogeneous mixtures of metals and cannot be separated into their components by physical methods. But still, an alloy is considered as a mixture because it shows the properties of its constituents and can have variable composition.
Q. Is it possible that an object is in the state of accelerated motion due to external force acting on it, but no work is being done by the force? Explain it with an example.
Ans.
Yes, it is possible, if an object is moving in a circular path because in that case the centripetal force always acts perpendicular to the direction of displacement.
For example: Consider the motion of earth around sun. The earth is constantly moving in a direction perpendicular to the gravitation pull of sun, hence work done by the gravitational force is zero.
hope it will help you
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who discovered vaccines for first time and why ?
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