Explain how defects in a metal block can be detected using ultrasound.
Ultrasounds can be used to detect cracks and flaws in metal blocks. Defects in metal blocks occur due to crack in them. Cracks have air in them. The speed of sound in metal is greater than that in air. Thus, air acts as a rarer medium for sound waves. Whenever ultrasound is transmitted through a metal block that has defects, these waves get reflected in encountering such cracks. Therefore, these waves are not detected at the detector placed on the other side of the block, opposite to that of the transmitter. This indicates that there is a defect in the block.
Convert into mole.
(a) 12 g of oxygen gas
(b) 20 g of water
(c) 22 g of carbon dioxide.
Why is the atmosphere essential for life?
What happens to the force between two objects, if
(i) the mass of one object is doubled?
(ii) the distance between the objects is doubled and tripled?
(iii) the masses of both objects are doubled?
You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?
Why are we normally advised to take bland and nourishing food when we are sick?
Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?
In which of the following case do you think the long-term effects on your health are likely to be most unpleasant?
• if you get jaundice,
• if you get lice,
• if you get acne.
Why?
Name the technique to separate
(i) butter from curd,
(ii) salt from sea-water,
(iii) camphor from salt.
What are the immunisation programmes available at the nearest health centre in your locality? Which of these diseases are the major health problems in your area?
A stone is released from the top of a tower of height 19.6 m. Calculate its final velocity.
Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?
Convert the following temperature to celsius scale:
a. 300 K b. 573 K.
A large truck and a car, both moving with a velocity of magnitude v, have a head-on collision and both of them come to a halt after that. If the collision lasts for 1 s:
(a) Which vehicle experiences the greater force of impact?
(b) Which vehicle experiences the greater change in momentum?
(c) Which vehicle experiences the greater acceleration?
(d) Why is the car likely to suffer more damage than the truck?
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.
List any three human activities that you think would lead to air pollution.
How will you find the valency of chlorine, sulphur and magnesium?
Why is the weight of an object on the moon 1/6th its weight on the earth?
How do good animal husbandry practices benefit farmers?
Using a horizontal force of 200 N, we intend to move a wooden cabinet across a floor at a constant velocity. What is the friction force that will be exerted on the cabinet?
How are sol, solution and suspension different from each other?