Class 8 Science Chapter 8 MCQ

Magnitude of force applied by A is greater than that of B because the block moves towards right i.e., towards B.

It will be magnetic force because as electric current flows through the coil, it behaves like electromagnet and magnetic force is created.

The electrostatic force is responsible for it, since on comparing the hair, the comb and hair get oppositely charged.

As we know that pressure exerted by the body is inversely proportional to the area where force is applied. So, which has less area of cross section in contact with the surface will exert more pressure on the ground. It is clear that height from the base exerts more pressure. Therefore, the maximum pressure is exerted when length and height form the base.

The reason for repulsion may be either an electrostatic (in case of similar charges) or a magnetic (in case of similar poles) force.

The force with which the earth pulls the objects towards it, is called the force of gravity. Gravity is a natural force of attraction or pull. If we drop a stone from some height, it falls down towards the earth. A leaf falls from the tree due to gravity. Rain falls down to earth due to the force of gravity. When we open a tap, water begins to flow down towards the ground due to the force of gravity. There are so many examples of gravitational force.

An electrostatic precipitator is a type of filter (dry scrubber) that uses static electricity to remove soot and ash from exhaust fumes before they exit the smokestacks. This one common air pollution control device. Most power stations burn fossil fuels such as coal or oil to generate electricity for use.

Here, all the statements are correct. Hence, your answer will be option [D].

The force “F” is all the same in all situation making it constant. Using the formula: Pressure=Force/area. This suggest that since “F” is constant, decrease in area will lead to increase in pressure and vice vasa. This may be represented by a real-life example with a sharp healed shoe of a lady and a normal shoe. If a lady weighing 140N may step on you while wearing the sharp healed shoe, the pain will be more severe than while wearing a normal flat shoe. Therefore, the lesser the area, the greater the pressure. Hence, your answer will be 10 m2, option [C].

Here, all the statements are correct. Hence, your answer will be option [D].

Atmospheric pressure is the pressure exerted by the atmosphere, or rather the weight of air above a point on Earth. It can be measured using a barometer. The unit of pressure is Pascals. As we go to a higher altitude on Earth, the weight of air above it decreases, so the pressure will also be lesser. So atmospheric pressure decreases with increasing elevation. Atmospheric pressure is measured using a barometer. At sea level, the barometer will read a value of standard or normal atmospheric pressure, equivalent to the pressure exerted by 760 mm or 76 cm, tall column of mercury or 101.3 kilopascals. Hence, your answer will be option [C].

Here, all the statements are correct. Hence, your answer will be option [D].

The rise in the level of mercury in glass tube of thermometer will not work due to the presence of atmospheric pressure. A thermometer works on the principle that mercury expands with increase in temperature. So, the mercury in a glass tube of thermometer will rise only due to increase in temperature.

Here, all the statements are correct. Hence, your answer will be option [D].

Here, all the statements are correct. Hence, your answer will be option [D].

A force can change the speed of a moving object. A force can change the direction of a moving object. A force can change the composition of a moving object. A force can change the shape and size of an object. But force cannot change the composition of a moving object or any object. Though composition is a chemical change.

Here, all the statements are correct. Hence, your answer will be option [D].

A force which can be exerted by an object on another object only through “physical touching” is called a contact force. Such as: i)Muscular force and ii)Friction force These are example of contact forces, but a force which can be exerted by an object on another object even from a distance (without touching) is called a non-contact force. Such as, i)Magnetic force ii)Electrostatic force and iii)Gravitational force

Force = 100 N, Area = 3 m2 Putting these values in the formula for pressure: Pressure = 100 N/2 m2 = 50 N/m2 Thus, the pressure is 50 newtons per square meter or 50 pascals.

The English scientist Isaac Newton had given the idea for gravitational force when he saw an apple fall from a tree. The force with which the earth pulls the objects towards it, is called the force of gravity. Gravity is a natural force of attraction. We are all pulled (including every object) to the earth by the force of gravity.

We can calculate pressure using the formula, Pressure = Force / Area. In this case, pressure = 10 kPa = 10 x 1000 = 10000 Pa and area = 0.3 m2. So, we can find force as follows: Force = Pressure x area = 10000 x 0.3 = 3000 Newtons. So, a force of 3000 N is required to create a pressure of 10 kPa for an object of area 0.3 m2.

A blunt knife does not cut an object easily because due to its thicker edge, the force of our hand falls over a larger area of the object and produces lesser pressure. This lesser pressure cuts the object with difficulty.

We know that the SI unit of pressure is pascal (Pa) but atmospheric pressure is usually measured in the unit of “millimeter of mercury” (mm of mercury) for the sake of convenience in measuring it. The atmospheric pressure on the surface of earth (at the sea level) is 760 mm of mercury.

The pressure depends on two factors: a) Force applied and b) Area over which force acts. Pressure = Force / Area Area = Pressure / Force = 500/ 5 = 100 cm2

When we press the rubber sucker on a flat, smooth surface, its concave rubber cup gets flattened to a large extent, pushing out most of the air from beneath it. Since, very little air remains inside the flattened rubber sucker, therefore, the air pressure inside the rubber sucker becomes very low (and a partial vacuum is created). The much greater atmospheric pressure acting on the rubber sucker from outside fixes the rubber sucker firmly on the flat surface.