Physics MCQs

Notes:
During winter ice is formed only on the top layer of a pond or a lake because the water’s surface is usually slightly cooler than the rest of the body of water due to evaporative cooling. As water cools below 4 C, it also becomes slightly less dense, rising to the surface. Ice is also slightly less dense than the slightly warmer water below, so it floats on the water’s surface. Once ice crystals begin to form, they provide nucleation sites for additional ice to grow along the water’s surface. The islands of ice expand, until they cover the entire surface of the water.

Notes:
It will fall to the surface. On Earth a hydrogen balloon floats only because it is less dense than the surrounding atmosphere. The Moon has no atmosphere, so the hydrogen in the balloon does nothing but add weight to the balloon.

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The layer of the atmosphere that reflects radio waves is the ionosphere. That is because there are gas particles in the ionosphere that are ionized.

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The middle component determines whether the lever is 1st, 2nd or 3rd class. 1st class levers have fulcrum in the middle, for example, Teeter-totter, scissors and pliers. Out of them, scissors and pliers are considered a double Class 1 levers. In 2nd class levers, the load is in the middle. Examples of this are Wheelbarrow and Nut crackers. In class 3rd lever, the effort is in the middle. Examples are Tweezers, Stapler, Mousetrap etc.

Notes:
Weight of a body is the force with which it is attracted towards the centre of earth. The weight of a body, ‘W’ of mass ‘m’ is given by: W = mg, where ‘g’ is the acceleration due to gravity. At the centre of earth, value of ‘g’ is zero. Therefore, weight of a body will be zero at the centre of the earth.

Notes:
Newton’s second law of motion can be formally stated as follows : The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

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Plotting distance against time tell us a lot about motion. If an object moves at a constant speed, it means it has the same increase in distance in a given time. In other words, the object moves at a constant speed which is shown by straight lines on a graph. Distance Time

Notes:
Hydraulic brake works on Pascal’s law which states that pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure variations remain the same. The wheel cylinder of hydraulic drum brakes acts as a double hydraulic press, multiplying the force on the fluid by the ratio of the area of the cylinder to the area of the supply line. Pascal’s principle guarantees that the pressure is transmitted equally to all parts of the enclosed fluid system.

Notes:
The extraction of cream happens because of the work of centrifugal force which works outward. The separation of cream from milk is based on the fact that when liquids of different specific gravities revolve around the same centre at the same distance with the same angular velocity, a greater centrifugal force is exerted on the heavier liquid than on the lighter one. Milk can be regarded as two liquids of different specific gravities, the serum and the fat.

Notes:
The waves produced on the surface of water in the pond is an example of transverse waves as particles of the medium do not move along with the wave. Only the disturbance (energy) is carried forward. Another example of such waves is the vibrations of a string energy.