Current Affairs 8th Class

Category : 8th Class

     Magnetic Force

A magnet is a material that attracts certain other types of the material towards itself. Such materials are called the magnetic material. For example, the materials like iron, nickel etc are attracted by the magnet. The force that attracts the magnetic material is called magnetic force. The magnet has two poles, north pole and south pole. Like poles repel each other and unlike poles attract each other. If we break a bar magnet into several pieces, each piece will behave like an independent magnet. We cannot separate the poles of the magnet.

       Rojer takes a rod and connects its one end with the electric current. He finds the rod behaves like a magnetic and exerts attractive force on magnetic material, such as, iron and nickel. The force which is being exerted by the rod is known as_________.

(a) Magnetic force

(b) Electrostatic force

(c) Electromagnetic force

(d) Nuclear force

(e) None of these

Answer: (c)

Explanation

The magnetic force that generates due to the electric current is called the electromagnetic force.

       Our earth behaves like a huge bar magnetic. All the object falling from a certain height is attracted towards the centre of the earth. The magnetic behavior of the earth is solely due to the certain elements present in the core of the earth. The elements due to which earth behave like a huge bar magnetic is ___?

(a) (Ni, Fe) 

(b) (Ni, Co)    

(c) (Fe, Co)    

(d) (Zn, Fe)

(e) None of these

Answer: (a)

Explanation

The element, which is present in the core of the earth and due to which it behaves like a magnet, is Ni and Fe.

            Electrostatic Force

An electrically charged object exerts force on an uncharged object. Such force is called the electrostatic force. For example, if you rub a plastic comb with your hair and bring the comb near the tiny piece of the paper, the piece of paper will either stick to the comb, or will start moving due the electrostatic force. Similarly, an ebonite rod when rubbed with the woolen cloth, it acquires the negative charge and attracts the tiny piece of paper.

        When a plastic comb is rubbed with hair, it acquires some charges due to which it attracts tiny pieces of paper. The types of charge, which the comb acquires form the hair is ____.

(a) Positive 

(b) Negative

(c) α charge

(d) β charge

(e) None of these

Answer: (b)

      Alford is wearing a woolen shirt at home. After some time, he starts feeling hot and takes off his shirt. While doing so he finds that, the hair on his skin got erected and are attracted towards the woolen shirt. Why is this happening with the wool?

(a) It lost charge   

(b) It gained charge

(c) Just a coincidence

(d) All of these

(e) None of these

Answer: (a)

Explanation

The above phenomenon is happening as the wool has gained charge from the hair of the skin.

         Effects of Forces

A force cannot be seen, only it can be felt. Its effect it produced when it acts on an object. The various effects of the force are:

(i) It can move the stationary objects

(ii) It can stop the moving objects

(iii) It can change the magnitude and direction of the object

(iv) It can change the shape and size of the object

        Units of Force

The force is always measured in Newton and is denoted by N. 1 Newton force is equivalent to the force required to accelerate one kilogram of mass, at the rate of one meter per second squared or Kgms-2.

Numerically, it is given by, F = m x a

Where, 'm' is the mass and 'a' is the acceleration.

           Some Other Units of Force

1 dyne = 10^–5 N

1 kilogram - force (kgf) or kilopound (kp) = 9.80665 N = 1 metric slug

1 Ibf = 32.174 poundals = 1 slug

1 kgf=2.2046 lbf

       The value of 1 dyne of force in Newton is ________.

(a) 10^–4 

(b) 10^–5

(c) 10^–6

(d) 10^–7

(e) None of these

Answer: (b)

Explanation

The value of one dyne of force is equivalent to the 10^–5.

The value of 1 metric slug in Newton is ____.

(a) 9.90666 

(b) 9.80665

(c) 9.90556

(d) 9.80556

(e) None of these

Answer: (b)

Explanation

The value of one metric slug in Newton is given by 9.80665.

• A person weighing 100 kg on earth will weight 38 kg on the surface of moon.
• The force of gravity 100 km above the surface of earth will decrease by 3%.
• Some roller coasters have gravitational force of 4 to 6 g.
• Due to friction the velocity of the body gets reduced, which leads to production of acceleration.
• During the race the tyres lose weight, and each tyre loses its weight by 0.5 kg due to wearing.

• Force is the push or pull of the object.
• According to the Newton's first law, an object in motion or an object at rest will remain in motion or at rest until and unless it is compelled by an external unbalance force.
• Inertia is the property of the object due to which it opposes the state of an object.
• The force, which opposes the motion of an object is called the frictional force.
• According to the Newton's second law, the rate of change of momentum is directly proportional to the force acting on the object.
• According to the Newton's third law, to each and every action there is equal and opposite reaction.
• Momentum is the product of mass and velocity.
• Law of conservation of momentum states that, total momentum before collision is equal to the total momentum after collision.
• The total momentum of an isolated system always remains conserved.
• A force of one Newton is defined as the force, which produces an acceleration of 1 m/s² on an object of mass 1 kg.