Physics MCQs
Topic Notes: Physics
MCQs and preparation resources for competitive exams, covering important concepts, past papers, and detailed explanations.
Plato
- Biography: Ancient Greek philosopher (427–347 BCE), student of Socrates and teacher of Aristotle, founder of the Academy in Athens.
- Important Ideas:
- Theory of Forms
- Philosopher-King
- Ideal State
1
What is the term for the insulating material placed between the plates of a capacitor?
Answer:
dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When placed between capacitor plates, it increases the capacitance by reducing the effective electric field between the plates for a given charge.
2
What is the term for the insulating material placed between the conducting plates of a capacitor?
Answer:
dielectric
A dielectric is an insulating material that can be polarized by an applied electric field. When placed between the plates of a capacitor, it increases the capacitor's ability to store electrical charge by reducing the electric field between the plates for a given voltage, thereby increasing the capacitance.
3
If a dielectric material with a constant of 7 is inserted into a parallel-plate capacitor originally containing air, how does the capacitance change?
Answer:
7C
The capacitance of a parallel-plate capacitor is given by C = ε₀A/d. When a dielectric material with a dielectric constant (relative permittivity) κ is inserted between the plates, the new capacitance becomes C' = κC. Given that the dielectric constant is 7, the new capacitance is 7 times the original capacitance, resulting in 7C.
4
How does the insertion of a dielectric glass plate between the plates of a capacitor, which is in series with a light bulb, affect the bulb's brightness?
Answer:
Increases
Inserting a dielectric material like glass increases the capacitance (C) of the capacitor. In an AC circuit, capacitive reactance (Xc) is inversely proportional to capacitance (Xc = 1/2πfC). As C increases, Xc decreases, which lowers the total impedance of the series circuit. According to Ohm's law for AC circuits, lower impedance results in higher current flow, thereby increasing the power dissipated by the bulb and making it brighter.
5
If a parallel plate capacitor with air as the dielectric has a capacitance C, what will be its new capacitance if the space between the plates is filled with a material having a dielectric constant of 7?
Answer:
7C
The capacitance of a parallel plate capacitor is given by C = ε0A/d. When a dielectric material with constant K is introduced, the new capacitance becomes C' = K * C. Given K = 7, the new capacitance is 7C.