Question

An experiment had two wires P and Q of the same resistance at room temperature. When the wires were heated, it was noticed that the resistance of wire P increased and that of wire Q decreased. What can be inferred from this experiment?
1. P is a conductor and Q is a semiconductor
2. P is a semiconductor and Q is a conductor
3. Both P and Q are conductors
4. Both P and Q are semiconductors

Answer 1

Correct Answer - Option 1 : P is a conductor and Q is a semiconductor

The correct answer is option 1) i.e. P is a conductor and Q is a semiconductor

CONCEPT:

• Resistance: The hindrance to the flow of current in a material is called electrical resistance.
  • The movement of free electrons in material causes a current. 
  • Resistance is inversely proportional to the current flowing in a material. 

EXPLANATION:

• Different materials behave differently on heating.
• Heat is a form of energy, and on heating an object, the electrons in it will have increased kinetic energy. 
• In conductors, the electrons will vibrate vigorously and undergo collisions with an increase in their kinetic energy.
• Each collision causes the electrons to slow down and thus, resistance increases.
• The electrons in a semiconductor require very little energy to excite to the conduction band.
• At higher temperatures, the electrons will have more energy to jump into the conduction band, and therefore, resistance decreases.    
• Thus, on increasing the temperature, resistance increases in a conductor and decreases in a semiconductor.
• Therefore, wire P is a conductor and wire Q is a semiconductor.