Test: Electric Charge Conductors and Insulators(25 Oct) - JEE MCQ

Insulators are materials that impede the free flow of electrons from atom to atom and molecule to molecule. Examples of insulators include plastics, paper, rubber, glass and dry air.

In contrast to insulators, Conductors are materials that permit electrons to flow freely from particle to particle. Examples of conductors include metals, aqueous solutions of salts (i.e., ionic compounds dissolved in water), graphite, and the human body.

We know that Current = Charge / Time

Also, 

Current = Ampere

Charge = Coulomb

Time = Second

1 ampere = 1 coulomb/ 1 sec

So, one coulomb is ampere times second.

• Electric charge between two bodies can be produced by rubbing with each other. This is known as triboelectric effect.
• The body having lower work function loses electron and becomes positive and the other body gains electrons become negative.

Example: When glass is rubbed with silk, glass becomes positive while silk becomes negative.

• If an object is positively charged it means it has lost some of its electrons.
• The mass of an electron is 9.11*10^-31 kg.
• So, if a positively charged body loses the ‘n’ number of electrons, its mass decreases by the amount n*9.11*10^-31kg.

To make an uncharged object have a negative charge we must increase negative charge particles in it and this can be done only by adding electrons to particles as electrons have negative charge.

So, the correct answer is to add some electrons. 

The correct option is D

In the direction opposite the electrical field

Conductors

1. Electrical conductors are materials that have free charges (electrons).
2. When conductors are placed inside an electric field, the charges experience an electrical force.
3. The charges rearrange themselves until they experience no more force.
4. As the electric field is switched on, electrons move against the electric field and accumulate on one side of the metal. Naturally, the other side gets positively charged. So, the result is an internal field due to the accumulation of charges.

Hence, the electrons will move in the direction opposite the electrical field.

Therefore, option (D) is correct

• On rubbing a rubber rod with wool, the electrons from the wool get transferred to the rubber rod.
• The wool now has a deficiency of electrons and so is positively charged.
• On the other hand, the rubber rod has an excess of electrons and hence is negatively charged.
• In the above example, the wool undergoes positive electrification.
• It is to be noted that it is the electrons and not the protons that get transferred during positive (and negative) electrification.
• Here, the transfer of electrons and mass transfer respectively takes place from wool to the rubber rod.

• He atom has 2 electrons.
• So, 1 mole of He has 2*N(N is Avogadro's no.) electrons.
• Then total -ve charge in 1 mole He gas is =  2 * N * charge of 1 electron
  = 2 * (6.022 * 10²³) * (1.6 * 10^-19) = 1.92 * 10⁵ C 

If we have two bodies with charge q₁ and q₂ on them and we are given q₁ + q₂ = 0. It means the net charge on the system is zero.

This is possible only if q₁ and q₂ are equal and opposite.

That is, q₁ = +q and q₂ = -q or vice versa. 

Such that, q₁ + q₂ = +q + (-q) = 0

• A body consists of atoms that have electrons, protons and neutrons. The electrons have a negative charge. The protons are positively charged and the neutrons are neutral.
• The atom is neutral because the positive and negative charges cancel out each other.
• On removing electrons, an excess of protons are present and thus the body is said to be positively charged.