Question

If two similar discs having unlike charges of equal magnitude are attached at the opposite ends of a metallic cylinder, then:
1. No current will flow through the cylinder
2. Continuous current starts flowing through the cylinder
3. Current will flow for a very short duration through the cylinder
4. None of these

Answer 1

Correct Answer - Option 3 : Current will flow for a very short duration through the cylinder

CONCEPT:

Electric current

• The quantity of charge passing through a given point of the conductor in one second is called electric current.
• SI unit - Ampere
• Mathematically, an electric current is written as

\(\Rightarrow I=\frac{Q}{t}\)

Where I = electric current, Q = charge and t = time

The electric current in the conductor:

• In atoms and molecules, the negatively charged electrons and the positively charged nuclei are bound to each other and are thus not free to move.
• In some materials, notably metals, some of the electrons are practically free to move within the bulk material. These materials, generally called conductors, develop electric currents in them when an electric field is applied.
• In some materials, the electrons are so bound that they will not accelerate even if an electric field is applied, these materials are called insulators.
• In solid conductors, the atoms are tightly bound to each other so that the current is carried by the negatively charged electrons.
• In an electrolytic solution, the current is carried by both positive and negative charges.

EXPLANATION:

• When two similar discs having unlike charges of equal magnitude are attached at the opposite ends of a metallic cylinder, an electric field will be created in the cylinder.
• The direction of the electric field will be from the positive charge towards the negative charge.
• The electrons will accelerate due to this electric field from the negatively charged disc towards the positively charged disc.
• The electrons thus move to neutralize the charges on the discs.
• As long as the electrons are moving, there will be an electric current in the cylinder.
• Once all the charges on the disc get neutralize, the electric current stops flowing in the cylinder.
• So there will be a current for a very short while. Hence, option 3 is correct.